1.0 DRAKE MODS (09 NOV, 1996) ______________________________ This document is considered public domain and you are free to distribute this document in its entirety without alteration. No fees or payment is to be granted or collected in the distribution of this material. While reasonable effort has been made to ensure accuracy of data, the author assumes no liability or responsibility for the consequences of any action on the part of any reader through the use of this information. Enclosed are a number of mods available for various pieces of Drake equipment of the 4 series and later. Some of these changes I have per- sonally implemented and some are collections from other sources. I've stayed on 'the straight and narrow' in providing nothing radical and kept the changes to the refinement level. What I've tried to do here is not only list the mods that I know of, but to share some of my experiences with the equipment. I've included some historical information and some thoughts on what the B and C series are about. A large part of the reason for this is that I've had to find this out myself - the hard way. A lot of the data is what I would of liked to have known before I started to acquire some of this gear. What surprised me most about this equipment is that there is almost no data external from Drake available. No mods - and I searched every where. No knowledge of what makes a particular example a good one. I was on my own, and try- ing to not just render my gear serviceable, but restore it also. Just what do you do with a mechanically unstable PTO? Is it possible to fix it? What is the VOX behavior of a properly operating TR7? And so on. With but one or two minor exceptions, every unit listed I have had some experience with, but not all of the mods have been deployed. Mods obvi- ously have been found. Some of them are from my having bought my latest flea market 'works great - just aligned' joy home, cracked the covers and WHOOOOOOA! Whats *this*? (ever seen someones attempt at turning a Heath HR20 into a base for a radio telescope? don't ask). You'll find this document a little different than most 'mod strings'. The reason for this is that if you screw up (say) a Kenwood mod, you just put the mess in a box, take it to a dealer and throw some money at him. Well, I'm sure you've noticed that Drake dealers are in short sup- ply these days. AND surprise surprise - while a lot of technicians might be able to service a multi loop PLL synthesizer, they have never seen a 12AX7 or have a clue just how a glassFET works. As a general rule, modifications are to be avoided unless there is a specific problem to be addressed or a refinement to be add. I strongly recommend that you do not make any equipment changes unless there is a good reason to do so. The only reason to modify a piece of well engi- neered equipment is to fix an oversight or add a capability that cur- rently does not exist. You should never modify equipment unless it is working as well as it could. Modifying equipment that is not working properly will only make it work .... worse.
Drake Mods (09 Nov, 1996) 1
1.1 GENERAL ____________ Comments in this section are generally common to all Drake 4 line equip- ment. o Some Notes Regarding V5 This listing seems to be well distributed. Please DO NOT strip the TR7 data out of this ZIP file. I've had people call me for this data as DRAKEMOD says it is included. The disclaimer says "... in its entirety". The entirety means the ZIP file that contains 3 files. I did inadvertently make a Drake enthusiast. This individual went out and bought a TR4Cw/RIT just from reading this and seems to be thrilled. This is quite a compliment. What I've learned through my use and ownership of this Drake equip- ment from R4B/T4X to the TR7 is that it is amazing how little you need to have some fun and yes, even be competitive. As has been proven time and time again in other pursuits, it is not the equip- ment as much as it is opportunity and user skill. High end equipment might make it easier ... and then again, maybe not. Well engineered equipment is eternal. Amateurs have been using CW since day one and SSB for 40 years. What applied then applies today and largely has not been improved upon all that much. Its gotten smaller, lighter and consumes much less power. However, it is not much more than application of modern technology to well established communications methodologies. My personal experience with other manufacturers Amateur equipment is not bigotry or xenophobia. The world has changed - a lot - in the last 5 years. Modern consumer electronics has invaded Amateur radio. What you can buy today, you'd have sold your soul for 10 years ago. Unfortunately, its unserviceable by most and like most products these days value evaporates in front of you. Whatever you buy new, such as personal computers and Amateur transceivers, is obsolete 6 months after purchase. Considering Amateur HF equipment, well engi- neered 'old tech' is applicable 90% of the time for 25% of the cost. And the average mortal can service it with basic test equipment and a reasonable application of theory. For whatever your reasons for enjoying Drake equipment - nostalgia, preference, curiosity or whatever I hope you find this useful. Worst case, then, at least an entertaining read. Here's DRAKEMD5. Enjoy. o Swap Nets Do not expect these nets to specialize entirely in Drake equipment. Some nets have specific rules regarding acceptable equipment to advertise. In general, no CB equipment unless modified to Amateur bands. Drake Mods (09 Nov, 1996) 2
The times mentioned are local Toronto time.
Tech tips and some equipment trading takes place.
o How Drakes Age Gracefully. All kidding aside, most Drake equipment will not self destruct un- less provoked. After all this time, just about any component that is going to fail, has. Here is a brief list of what is likely to happen with a Drake over time: - Electrolytics dry out - Some ceramic capacitors fry from excessive heat. - Preselector verniers wear - Worn switches - selector tabs - PTO end play needs adjustment - PTO lubricant dried out - Tube failures - User modifications Drake Mods (09 Nov, 1996) 3
Not much, really. You can use this as a check list of what to look for or what to service when you buy your 'new' Drake. The first 8 items or so are operational and not cosmetic. o PTO End Play If the tuning knob can be wiggled from side to side, chances are the end play needs adjustment. End play can be adjusted by tightening the ball bearing on the PTO tuning worm gear. Some Drake equipment might have an extra hole on the PTO cover for this purpose. For those that do not, you must re- move the PTO cover. Use a long 3/32" allen (hex) wrench. The adjust- ment 'nut' in question is recessed beneath the coil form. Do not overtighten or you will ruin the dial drive ball bearings and race. Do not disturb any placement of components or you will affect the PTO dial tracking. o PTO General Notes Most of the PTO units are much the same throughout the 4 line, but the drive mechanisms and indicator plates are not. The worst things you can do to a Drake PTO is to continue tuning past the STOP indi- cation or clean the dial plates with something that dissolves the Drake Mods (09 Nov, 1996) 4
plastic. Be very careful with cleaner on those Lexan dial plates! If in doubt, use mild soap and warm water. Dial plate replacement is impossible (there are no dial plates to be had). Drake will service the PTO for you - they have the gears and other mechanical parts and can reset the PTO for drift and linearity spec. It would be most wise, however, to not lunch the PTO gears and dial plate. o PTO Evolution The PTO stayed basically the same over the years. It is a good, solid design. Early model PTO assemblies had a brass pin that was driven into a slot in the gear to provide a stop. As these assem- blies wore, sometimes the pin would not extract itself and the PTO drive would end up in a locked state. If this was forced, the pin will snap, leaving no dial stop at all and the dial plate will go around and around until the slug bottoms. Later assemblies used nylon gears and dual dial plates on a concen- tric shaft. Some of these dial plates are 3 pin and some are 2 pin. The number of pins refers to the brass rivets that hold the dial plates to the gear faces. There is no stop to speak of in these assemblies and turning past the mechanical resistance of the drive assembly will lunch the gears. These PTO drive assemblies may have 'ears' and there may be 2 ears just behind the gear assemblies. The purpose of these ears is to allow the dial plates to be rotated for proper mechanical orientation with the dial window gradical. o PTO Mechanical Instability This is usually caused by either the worm gear tension spring not hooked to the aluminium PTO cover or by the end cap on the end of the PTO coil form being loose. If the problem is not the tension spring, remove the PTO cover and look at the end of the PTO coil form. You will see a cap on the end of it. It should not be loose. If it is loose, carefully remove it, apply some glue and stick it back on. The coil form is delicate! The end cap just has a square hole through which the tuning slug brass rod goes through. For glue, I use GOOP. See also PTO End Play above. o PTO Warble Sometimes the PTO will warble slightly while tuning. This is usually caused by dried out grease on the drive mech ball bearings. This is the ground path for the PTO slug drive which has a brass rod inside. Fix the dried out grease problem first. Use Teflon lube or Lubriplate. Run a flexible ground strap from the PTO drive yoke to ground. Do not grease or lube the top guide pin for the PTO slug yoke. o PTO Lockup - B Series
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Sometimes the brass pin will insert into the gear at the 'STOP' area, but it will not extract itself, causing the PTO assembly to lock up. Wear will cause this, but in a lot of cases its caused by the gear timing being off a little bit. What happens is that you'll buy a used 'B' and use it. One day, you'll hit the stop, and the pin will lock the PTO. Oh Oh - whats *this*? Unlock the PTO first by pushing the stop pin back and rotate the tuning knob. Looking at the front of the radio, you'll notice a ny- lon gear thats spring loaded. Gently push this gear back and rotate the tuning knob ever so slightly (which way? take your pick). Now run the PTO to the stop again and see if the pin extracts. No? You went the wrong way or there are more serious problems. o PTO Lubrication Given the age of these unit, the grease is starting to dry out. Its possible that it may even has run away slightly after seeing God knows what use in a car or in a hot tent on Field Day many years ago. Most important is to lubricate that worm gear. I use Teflon spray lube. Just use the slightest bit. Too much is much worse than too little. The dial mech should offer only slight resistance to the tuning knob. You should be able to fast spin the tuning knob by placing your index finger on the outside of the knob and rotating your hand. If you cannot do this, then you have some kind of a prob- lem in the PTO dial mech. o PTO Backlash Inspect the brass rod that extends from the rear of the PTO cover as the unit is tuned. It may be discolored, but it should not be cov- ered in grease and guck. This rod and the end of the PTO tuning coil comprise the end bearing. Clean with alcohol and a paper towel. Sometimes 'junk' will accumulate in this area and actually cause some binding in the tuning slug. You'll tune the PTO and in about 5 minutes, it will 'jump' frequency up to a few hundred cycles. o PTO Drift All Drakes drift. Once warmed up and settled down, they are satis- factory for all modes but RTTY. For all practical purposes, the PTO from the B series to the TR7 (excluding the TR5) are identical with the exception of the dial plates and the markings on the aluminium cover box. In very general terms, the PTO should settle down within about 5 minutes after turn on and be usable. It will still shuffle around a bit after that, but you should not be chasing it continuously. There are no PTO adjustments available to compensate for drift; components were 'selected in production'. In extreme cases, you will either replace the PTO from a junker or send the unit to Drake for a rebuild. Expect to pay for 4 quarter hours labor minimum. Drake Mods (09 Nov, 1996) 6
Inability to have the C line dial plates to indicate exactly the same frequency after moving away 100 kHz or so and returning to the same frequency is usually caused by the rubber collar under tuning knob and dish. After all these years, the rubber has hardened or has worn. Replace the PTO rubber. The C clip should not be tight against the aluminum washer and the washer should be installed such that the groove around the perimeter is on the outside. While you've got the knob and dish off, inspect the shaft for burrs. Sometimes when you push a new rubber collar on you'll displace one of the gear sets. This is easy to fix, but you'll have to remove the top cover, push the left hand ear to the right while gently rocking the tuning shaft and pulling out. Then align the dial plates again. A new collar should last for years. o 4 Line Dial Plate Dish, Knobs etc. Personally, I don't like the plain dial skirt on the C line. I re- place them with TR4 dial dishes. This does nothing except for appearance and is a matter of personal taste. The TR7 dial dish is different than the 4 dial dish. Some dial knobs are thicker than others depending on the PTO assem- bly. Most knobs are available for replacement except for TR7 bandswitch knobs. Unobtainium. o Mixing Scheme First mixer injection on all T4/R4 is premixed from the PTO and the band crystal. The crystal is always 11.1 MHz higher than the low end of the band edge in question. For example, the 80 meter band will have 3.5 + 11.1 = 14.6 MHz crystal. The PTO is mixed with the band crystal and the difference is used and injected into the first mixer. A lower PTO frequency correlates to a higher received fre- quency in the band range. Using 160 meters with a 12.6 MHz band crystal for example, the 0 scale band edge is 1.5 MHz. The first mixer injection frequency is Fin + Fif = 1.5 + 5.645 = 7.145. This is made from the difference of the PTO = Fxtal - Finj = 12.6 - 7.145 = 5.455 MHz. If you apply the above scenario to a 2.0 MHz incoming signal you will see that the PTO oscillator frequency tuning is inverted. Both the R4any and SPR-4 are remarkably low in spurs and mixing pro- ducts once aligned properly. On all of these receivers, I've always noticed a quickly tuning spur at 3.897 MHz. This tunes very fast, so a VFO harmonic is involved. Because of the PTO frequencies and mixing scheme there are some for- bidden zones of operation on some band segments that will produce Drake Mods (09 Nov, 1996) 7
very foul mixing products. Obviously the band range covered by the PTO is a no-no. 10 MHz operation is possible, but pay attention to the transmitter manual, for the PTO second harmonic is an important ___________ consideration when the twins are set up for transceive operation. None of these zones fall into current amateur band assignments. This also explains why strange settings of the preselector control produce receive peaking - you are likely finding a mixer output that could be PTO, crystal or the sum of the PTO/crystal product that coincides with the rack slugs for the front end tuning. o R4any and T4any Transceive Operation Transceive selection and muting is accomplished through the INJ line. This is done by supplying a high negative voltage along this line from the unit with the active PTO. This line is routed to the ____ link on the preselector and to the control grid of the PTO/xtal LO premixer. There is also a diode on the preselector mixer more or less from screen grid to plate. This forms an electronic switch to kill the premix on the unit that is having the external PTO premix signal. On the R4C/T4C there is also a separate BFO line. The oscillators on both units will fall into sync with each other naturally just from being linked together, providing they were pretty close together to begin with. If the BFOs won't sync, make sure you are using RG/62U cable and that the oscillators individually are pretty close. o Mixing Scheme - TR4any The TR4 uses the same PTO as the rest of the 4 line, but it has a 9 MHz IF. It covers 80 to 10 meters. Hetrodyne mixer crystals are not used on 80 or 20 meters. For these two bands, either the sum of the IF and PTO is used (20 meters) or the difference (80 meters). Thats why 20 meters has its unique dial markings that are backwards to the rest of the bands. All other bands have premix crystals and follow the formula of Fxtal = F + 9 + 5.0. The injection into the first mixer is 9 MHz ABOVE the the lower band edge and is made up from the band crystal frequency MINUS 5. All crystals are HC/6U 3rd overtone. This is accurate for all bands but 80/20. In this case no crystal is used and the 5-ish MHz PTO is used directly. The 6EA8 PTO premix circuitry is diabolicly ingenious in how it uses and does without a crystal oscillator depending upon the band switch. Having a TR4 operate on different bands is more of an operation than simply changing crystals. The front end is tuned by a variable capacitor, not by slug racks as in the case of the R4any. Moving a TR4 to the WARC bands, say 18 MHz in exchange for 20 cannot be done (no crystal, remember?). Generally, what you see is what you're going to have and depending upon what you do and how you do it, be prepared to kiss 15 meters goodbye. That band 'falls' into alignment by default from the alignment of the other bands being accurate. Drake Mods (09 Nov, 1996) 8
These are not available from Drake any more. Use cleaning materials with extreme caution. Most minor scratching of clear plastics can be polished out with toothpaste, a touch of water and a paper towel. This works amazingly well. If you use this trick on the dial plates, be careful you do not rub the lettering off. Gel does not work nearly as well as toothpaste. o C Line Dial Alignment The C line allowed for dial indication alignment through the use of idler gears in the dial drive mech. Just to the left and right of the drive transmission you will find one or two 'ears'. Pushing these ears towards the PTO shaft will allow the indicator plates to be rotated such that the plates align to display the correct fre- quency. Depending upon the age of the C line unit in question, there may only be one ear. In order to reseat the idler gear, push the le- ver over and let go such that it snaps into place. If you do not do this, it will take some rotation of the tuning knob until the idler seats and your alignement will be off (again!). On the B, you can rotate the Lexan dial plate a little with a touch of brute force. Place a small screwdriver on the edge of the dial plate and flick it the few necessary degrees. Do not to this with the C line (see above). o Dial Plate Scraping The dial plates are fairly large diameter Lexan disks. On the C line, there are 2 of them. One knob turn tunes the receiver 25 kHz. Sometimes the dial plates will scrape as they are rotated usually somewhere around the front panel. Over the years, some heat warping should be expected. Quite often though the scraping is caused by poor assembly after removing the front panel for cleaning. If the whole PTO had been removed, there is a little positioning adjustment available if the 3 PTO nuts are loosened. Ensure the dial gradical plastic is on the outside of the sub chas- sis with the red line on the inside of the window (C line). On all radios, the blue filter mounts on the back of the white plas- tic dial backing. Make sure the dial light wires are positioned away from the dial plates. o R4any and T4any Tuning Rack Leave the slugs alone! There should never be a valid reason to pull a tuning rack apart except under the most unusual of circumstances. These slugs are color coded for permeability - mix them up during reassembly and you'll have a fun time getting the receiver to track Drake Mods (09 Nov, 1996) 9
Sometimes you may encounter either a dead radio or an intermitent one and just can't find the sore spot. Check the rotary switches for a sawed off selector tab. Sometimes just enough of a stub is left to select some positions - just barely. This is just wear and tear and is simply the rubbing action of the selector tab going past the fin- gers. o T4any Microphone Connector The microphone connector plug is a Switchcraft S230 and has a diam- eter of .210". This was used so you couldn't plug the microphone into the earphone connector and have the output fry the element. These plugs are a little rare. The reason why the PTT line is the tip and not the ring is simple. If it were the other way around, you'd put the keyed line across the mic element as you pushed the connector in. In desperation, I've seen a standard 1/4" stereo socket used and it could be an expensive expedient. Microphones don't make good speakers or speakers for very long. These connector assemblies are no longer manufactured by Switchcraft, although there is possibility of a limited production run. Check with Mouser Electronics regarding status (Oct, 1996). o T4 and TR4 Relay Cycling With the age of these units some of the electrolytics are starting to dry out. Sometimes they'll go leaky from cell to cell if there are multiples in the can. If you have problems with the T/R relay chattering or cycling, quite likely it could be one of these filter cans. The only way to roughly suspect an element has gone is to clip in a 100 Uf 300 volts across an element. If the cycling stops or slows down this is the likely problem. Beware of some funny problems you may get with cell to cell leakage, however. These can be tricky to nail. These canned capacitors are dated and largely unavailable as re- placements. Due to their age, even if replacements were available, you wouldn't want them. Whether in use or not, they've been sitting on the shelves for too long. Modern capacitors are much better. My recommendation is to replace the whole can with discrete electrolytics. You can either leave the old cap in there for appear- ances or pull it and put in a hole plug. In the receivers, weak power supply electolytics are characterized by hum, low B+ and 'funny' audio on SSB. The funny audio is caused by harmonic mixing of the 60/120 cycle hum and the detected audio. In this case, sometimes there is not enough hum out the speaker to be too objectionable, but the speaker audio sounds 'funny' for some reason or another. You can verify this with the calibrator on SSB. Drake Mods (09 Nov, 1996) 10
As you sweep across the calibrator slowly, you'll hear some spots where the audio goes muddy. Once you detect it, and have your ears trained, its very obvious. o Schematic Date Codes On the 4 line B series and above you'll notice a series of numbers in small print on the schematic. I have an T4C schematic with the numbers 10077626470. This is in mmddyy/serial no format. It means that this schematic was revised on October 7, 1976 and applies to serial numbers above 26470. I do not see this notation after the TR4Cw-RIT. o Drake Equipment Wiring Drake did not color code their wiring to any appreciable degree. In most cases, their hook up wiring seems to be white colored and some wires may have a color trace. More than one wire may have the same color trace, so be careful and verify with an ohm meter from end to end. Additional care should be used when soldering to Drake hook up wire. The insulation melts very, very easily and will crawl up the wire and peel off while doing so. When replacing items like those canned filter caps, sometimes it causes less damage and is more expedient to simply cut the wires. One can easily and quickly loose 3/4" of insulation just in desoldering. o Line Cords Some line cords will be 2 wire - no ground pin. This may appear on the receivers or on the AC4 transmitter power supply. Users are urged to change the line cord to a 3 wire configuration with a grounded centre pin. Without this centre pin, the chassis leakage will float to about 50 volts AC. In the event of the primary windings shorting to the chassis, this can prove to be lethal. Don't put this off! Replace that line cord. o Loose Knobs On some controls it may be difficult to keep the knobs tight to the shaft. Overtightening will split the knob. Quite often the problem is simply caused by the knob not being exactly square to the shaft flat when the set screw is being tightened. Rock the knob slightly while tightening the setscrew. The knob setscrews are not all that easy to deal with in the long term. A better setscrew is an Allen (hex) head screw. This type of setscrew will provide better torque control. o Sensitivity Check - all Drake 4 line All Drake receivers and transceiver should provide a noise peak as the preselector is passed across the tuning range, even on 10 me- Drake Mods (09 Nov, 1996) 11
ters. If your equipment does this with no antenna connected, you have all the sensitivity you can use. If it fails to provide a peak, alignment is immediately suspect. Generally, the calibrator should provide an S9 meter reading on 10 meters, progressively increasing as the band switch is rotated to 80 meters. o Front Panel The 4 line has spacers in the 4 corners of the front panel. Be care- ful when you remove the front panel. The thickness of the spacers seems to be 1/16" or so and they are, of course, black. They disap- pear as soon as they hit the ground. o Screws and fittings There are no metric fittings that I know of. Most of the machine screws are 4/40, the case cover screws are 6/32 and the chassis sheet metal screws are usually #4. o Speakers All Drake equipment is standardized to 4 ohm speakers. This impedance is important. Use of 8 ohm speakers will produce consid- erably less audio output and is not recommended. On all the Drake C line and before, as in all audio power stages that have an output transformer, never crank up the audio gain with- out a speaker attached. Never connect an A/C voltmeter across the primary. Transients generated in the output transformer, especially without a load, will create very high voltage spikes through the collapsing magnetic field. This is how output tubes arc, output transformers short and voltmeter rectifiers get punctured. o Power Supplies The Drake vaccuum tube transmitters and transceivers use the same AC/3 or AC/4 supply. When using alternate supplies such as the Heath HP-20 or HP-23 ensure that the low voltage 250 volt supply is indeed this level. Do not provide more than 265 on this power line. o Transmitter Meter PA Current Resistor When you buy your 'new' Drake, check the value of this resistor. I've seen a number of these cooked. Usually they go higher in value, causing a number of problems. With the resistor higher in value, the meter will read higher. You'll end up setting the bias too low, causing poor transmitted audio. It would be wise to verify the meter calibration against the idling current. Using the T4C for example, it has its PA bias set for 70 ma and has a meter resistor of 3.3 ohms. Set to 70 ma, you should meas- ure E=I*R, or .07*3.3 or .231 volts across this resistor. Measure across the resistor and NOT at the meter terminals. Drake Mods (09 Nov, 1996) 12
Similar problems with setting the proper idling current will be ob- served if the PA current meter needle is not resting at zero. o Intermitents Some intermitents may be difficult to find and somewhat hard to ex- plain. Inspect the bottom of the chassis carefully and you will ob- serve screws holding down terminal strips and circuit boards. All the screws that you can easily access should be backed off 1/2 turn and retightened. A TR3 suffered the above problems and was cured by the above ap- proach. Most of this equipment is 20 years old or older. In the case of the TR3, it was 33 years. The obvious suspect is corrosion. o Drake Tube Transmitters - ALC On all Drake Tany and TRany radios, the transmitter ALC is very aggressive. In use, you won't see the output meter kick up that much or the PA current on the meter of the transceivers move as much as you think it should. Usually an output meter will 'only' indicate about 50 watts or so. This is 'OK' and is *not* an indication of low sideband output. Actually, this is normal behavior and if your transmitters do not behave this way, expect some ALC problems. For a typical Sure 444 or Heath HDP-21 microphone, the transmit au- dio gain/drive control should be set around the 11 o'clock position and the PA current meter should kick up to about 50% full current (150 ma, T4; 220 ma, TR4). o Transmitter switching For all receivers and transmitters in the 4 series the keyed voltage level is negative. The TR7 has a positive switch line. o Transmitter Driver Alignment Drake goes into considerable detail on use of a loading network to align the 4 series transmitters. Don't bother. Just align carefully for maximum transmitter output at a low drive level. The reason for this network is to simulate the loading when the units are used in transceive. The better method is to slave the units with the covers off both the receiver and transmitter and align. This is much faster and much safer than playing with the loading network method. There is some serious voltage inside these units. Align each individual unit and then align in transceive both ways - active PTO in the receiver for the transmitter and con- versely. When setting up in transceive, you really only need to touch up the most rear trimmer bank in the receiver and the front bank in the transmitter. It is not as much a pain as you would think and once set, you're done almost for life. The loading network method is a waste of time. Drake Mods (09 Nov, 1996) 13
Proper set up of the neutralization is important for a stable, easy to tune, low spur transmitter. I've seen numerous methods over the years, but this works best for me. What you want to do is set the neutralization capacitor such that the plate current dip and output occur at the same point in the final tuning controls. You need a decent dummy load. Start on 20 meters and feed enough drive in the tune position for about 200 ma of current. With the LOAD capacitor at maximum (lightly loaded), tune for maximum output on the wattmeter. Now watch the plate current meter as you rotate it off resonance. Does it dip lower? Take the transmitter (transceiver) out of 'tune' and adjust the neutralization trimmer about 10 degrees. Repeat until dip and maximum output occur at the same time. Once you have it set up on 20, then move to 10 (or 15). The reason for starting on 20 meters is for safety. If the neutralization is far out to begin with, the PA stage will oscil- late. It is also easier to adjust initially on a lower frequency. WARNING: The neutralization trimmer has a lethal voltage on it! DO NOT adjust with the transmitter operation, DO NOT touch the blade of the screwdriver while adjusting. Or go ahead. Ignore these warnings. I'll have less QRM to contend with. o Transmitter Tuning The best final tubes to use are Sylvania. The 'generic' 6JB6 are OK, but they can present alignment problems. The 6JB6 tubes will draw considerable current. On the TR4, they can draw upwards to 450 ma. The T4 will draw 325 or so. When tuning up, keep the drive level on either unit to 150 ma or less until you're close to the final settings. Low PA tube life is usually caused by bias setting, operator, SWR, heat or PA neutralization. The 6JB6 tubes are being pushed a bit, but they should offer a good service life if properly set up, oper- ated and kept reasonably cool. I've heard that tubes don't need cooling since its the glass that's getting hot, but the real heat is on the plate, insulated by a vaccuum. Nice theory, but my experience indicates otherwise. Besides, if for no other reason, all that heat cannot be good for component life. o Transceive Operating Any of the 4 line separates will transceive amongst themselves but only within the same band and only within about 50 kHz, depending on the band. When there is a difference in the series set to transceive Drake Mods (09 Nov, 1996) 14
some minor inconveniences will be suffered such as loss of active PTO indication and the requirement of BFO netting prior to oper- ation. But it will work. o T4B/R4B Transceive Set Up Since this equipment does not have a separate BFO injection line, you must net them manually in order for them to transceive properly. The C line provided a separate line. There is more to this, however. Before netting the two together, you should verify the BFO frequency of the T4any is on frequency. It is shifted for CW operation. If it is off frequency, then netting the two together may cause the offset to be quite wrong on CW. Proper netting on the T4any is best done with a receiver that does not shift frequency between upper and lower sidebands (like a Drake). Talk into the TX on a dummy load while tuning a known prop- erly set up receiver using headphones. Switch to the opposite sideband and adjust the BFO trimmer on the transmitter to exactly the same pitch/frequency. You may have to do this a few times. o C Line Meter Switching The C line used an articulated LOAD control shaft that, when pushed in, would switch the meter from PA cathode current to relative out- put. The push required is considerable and is a result of the spring strip tension and the spring in the return switch. Never try to ad- just the tension of the shaft spring strip by squeezing it. The bend in the metal strip is a stress point and the strip will fracture at the bend. There are no replacement shafts to be had. If the tension is abnormally high, ensure that the shaft coupler and the shaft it- self are completely seated to the LOAD variable capacitor. o Noise Blanker Set Up Both the R4C and TR4 noise blankers are very effective. The align- ment of either is not difficult except in the case of the TR4 where access to some tuning adjustments can be a challenge. You'll need a 'scope to completely set one up and/or an analogue me- ter. Digital meters are OK, but they don't show relative measure- ments very well. The components in parenthesis are TR4 part tags for the 34PNB. Turn equipment on (what else?), turn noise blanker and calibrator on. Tune calibrator in on 10 meters and misadjust preselector for about an S3 reading. Adjust C3 and C6 (C10 and C19) for maximum S meter reading. Place a 'scope probe to the base of Q12 (Q12) or a voltmeter to the emitter of Q14 (Q14). Peak preselector. Adjust C19 and C25 (C8 and C21) for maximum. Turn off calibrator. Set the Drake Mods (09 Nov, 1996) 15
'scope probe for 1/10 (low capacity probe). All tuning adjustments are finished. No more trimmer twiddling from this point! Place 'scope probe to drains of Q7 and Q8 (Q6 and Q7) and adjust R28 for minimum. Finally, on the R4C only, adjust the gain balance for simi- lar S meter reading on the calibrator with and without the noise blanker and the jumper plug. If you do not have a 'scope to adjust R28, leave it alone or more or less centre the control. o Transmitter filament Fuse Most Drake transmitters and transceivers have a fuse in the filament power. This fuse may be a strand of copper wire or a pig tail fuse. It is a wise safety feature and prevents the wiring harness from go- ing up in smoke should a tube filament short. Pig tail fuses are hard to find and single strands are cheap, but a pain to create. Should your fuse open, install a fuse block for a 3AG fuse holder by bolting through one of the chassis perf holes. This is a no holes mod and worth while. Don't forget to find out why the fuse opened in the first place. Sometimes, they DO just 'go'. o Carrier Balance (all transmitters and transceivers) The procedure in the manual is to use the relative output meter for carrier balance adjustment. The output meter is not sensitive enough to do this adjustment properly. Use an external receiver and make sure the mic gain is fully CCW. You should be able to almost null the carrier out completely. o Crystal Filters - Hope Rumor has started that the original manufacturer of Drake filters is about to begin production as of mid October, 1996. This has yet to be confirmed, but if it is true, filters should be available by the end of the year. If they do not appear by then, all bets are off. o R L Drake Inc Drake has in stock replacement parts for most of their equipment. For items that are in excess of 15 years old, this is very good. In most cases their prices are good. One can obtain coils, crystals, tubes, meters and relays. Final variable capacitors are available, but expensive. Most front panels are available for around $15.00 but Drake won't sell you a new one unless you return the old one. I do not know why, but Drake is adament on this policy. If you write Drake a letter they will ship off a computer listing of current parts stock for a particular radio. As of the Summer of 1995, considerable parts were available for the 4 line et al. Parts for the TR7 were few except for ICs and transistors.
Drake Mods (09 Nov, 1996) 16
There are no accessories available of any consequence. You will not be able to buy noise blankers or crystal filters for any of the C Line. If you want crystal filters, there is only one known source - International in Florida. Their filters are much better than what Drake supplied and expensive. Well, maybe not that expensive con- sidering current KenYaeCom prices. And even their filters are infe- rior to Internationals. Essential parts are still available (until the stock is gone) at reasonable prices. If you need accessories for your R4C or TR7, best to get them with the radio. Drake still services all of their amateur equipment, but they do not stock the PA tubes. They charge by the 1/4 hr. The current rate is about $17 US. I have heard some 'mutterings' about the labor cost, but have yet to hear ANY complaint about the quality of the work done. Consider Drake your only commercial repair service area, espe- cially in the case of the TR7. The TR7 (and possibly other equipment in the '7' series) requires a fairly high skill set to service prop- erly. Most, if not all 'dealers' of the, uh, other equipment won't touch it. Use this as a warning also for some Drake equipment on the dealer shelves, again, especially the TR7. Most are consignment sales. Consider its status as 'indeterminate'.
1.2 WHAT DISTINGUISHED THE C LINE? ___________________________________ The differences between the B and C line receivers will be discussed in separate detail. Even the C line receivers were different as the years progressed. There is an overall difference between the C line and much of went before, however. The B line employed copper plated chassis. In the C, this was done away with. The C series also employed dual concentric dial plates where the B series and even the T4X used a single dial plate. The knob skirt on the C line was plain; on the B it was calibrated in kHz and on the TR4 this dial skirt just had radial markings with no numbers. Generally, in the receivers, Drake made optional on the C a number of things that were standard on the B. The B was a complete receiver out of the box; the C was not. The B automatically switched the AGC as the modes were changed; the C receiver had a 3 position AGC decay time con- stant setting that was independant of mode. Additionally, the C receiver allowed for more optional band select crystals. The primary reason for the triple conversion on the C was to allow for crystal filter selection and a notch filter. Pundits could argue the necessity of this, but regardless, thats what Drake did. In the transmitters, Drake switched from a 6HS6 LO premixer to a 6EH7 on the C line. This is a higher gain tube, but still, the B series did not suffer from a lack of drive. The 12BY7 was used as a driver tube throughout the 4 line. Drake used 6JB6 tubes for the final PA in all of Drake Mods (09 Nov, 1996) 17
their C and B line transmitters. In the transceivers 3 of these tubes were used to produce 200 watts output. On the separate transmitters, 2 of these tubes were used to produce about 150 watts on 80. Most of the changes in the C transmitter were for operator convenience. The C series most notably moved the switch for PA current from a sepa- rate control on the B to a switch that was activated by pushing the load control in. The C line also improved upon transceive operation of the separates by providing a separate line for the BFO. This alleviated the requirement to set the receiver and transmitter oscillators exact by the 'canary chirp' method. Additional switch lines were also provided to the dial lamps to indicate the active VFO when slaved together in the C line. Despite these changes, the B and C series could be slaved together. While the TR7 and TR4 were not transceive compatible with the separate receivers, they still provided for external receive antenna switching and external RX mute. Drake took measures to provide for an intermix of their equipment despite improvements to the gear as the years prog- ressed.
1.3 R4B AND R4C ________________ You could liken the Drake twins operationally to the Heath SB301 and SB401 from the fact that they would transceive. Stand alone SSB trans- mitters are all pretty much the same. The T4C is a bit like an SB401 functionally. In regards to the SB301, the Drake 4 line receiver, espe- cially the R4C, is in a completely different league. All Drake receivers in this series are sensitive and selective. On ei- ther series, a healthy receiver should exhibit noise peaking on all bands as the preselector is adjusted with no antenna connected. It will not be an extreme increase in noise level, but it should definitely be there on all bands. Drake enthusiasts generally prefer the B series receiver. The B series has built in a number of items that were options on the R4C. There are few mods for the R4B. When you buy an R4B, there is not much else to get - EVERYTHING is there that you need - noise blanker, calibrator and 4 selectivity settings. The B series was dual conversion, the last IF at 50 kHz determined the selectivity and provided notch filtering. The B receiver is noted for its clean recovered audio, good signal handling and solid engineering. Because the selectivity is determined by LC fil- ters, the skirt selectivity is not on par with crystal filter radios. Since the B receiver was dual conversion and the C receiver is triple, it is generally assumed that the B receiver is 'quieter'. This will ap- pear from time to time throughout this treatis and I'm skeptical whether this is in fact true or yet another example of theory not born out in practice. Drake Mods (09 Nov, 1996) 18
The noise blanker in the B receiver works quite well, but not as good as the R4C or TR4 blanker. The B blanker is more sensitive to noise 'qual- ity' - duration, period and rise time. Some noise will be nearly elimi- nated and yet other noise which sounds the same won't be touched. The R4C and TR4 blankers are more effective across broader noise charac- teristics. The R4B blanker is a 'Lamb IF Noise Silencer'. Detail on its workings can be found in most Handbooks dated around 1972. Intermod characteristics are not degraded in either receiver with the noise blanker turned on. The R4C is in fairly high demand. It is a triple conversion receiver and completely different from an R4B. While the R4B does contain some semi conductors, the R4C is more of a hybrid design. There were at least 3 different types of R4C receivers. Generally an early R4C has a 4 posi- tion crystal filter switch and a later model has a 5 position switch. In the later model, the AM filter location was moved inside the chassis and mounted on an extra bracket. There is no discernible performance difference amongst ANY of the Drake R4C series receivers. Collectors want the later model; practical owners shouldn't care. The R4C - in all models - came with an 'OK' sideband filter. You will need to upgrade the filters and add some filters if you want to get this receiver to perform. There is only one source of filters for the R4C and that is International Radio in Florida. These filters are expensive (about $110 ea. US) and excellent. The most important filter is the 8 kHz first IF filter known as a GUF-1. Replacing the stock Drake filter with the GUF-1 transforms the receiver. If you have the 6 kHz GUF-1 in- stalled, noise blanker performance is compromised. The GUF series filter is difficult to obtain and they are not drop in replacements. You will be required to drill holes in the chassis or build an adaptor board from double sided G10 and mount the assembly underneath using some stand offs. The results are worth it, however. A stock R4C is a bit of a waste. Under those covers is goodness just dy- ing to get out. When the R4C came out, there were some compromises that had to be made to keep the price point. The trade offs were mostly in the area of filters and no noise blanker. The first IF amp crystal fil- ter is a pretty sad excuse and unfortunately sets the character of the receiver. What you have to do to make it what it could of been is to ba- sically un-castrate it. With decent filtering and maybe some mods, the receiver is as good as and maybe better than just about anything avail- able to date. Some aspects of the R4C design cause one to question the engineers at Drake. The audio amp in the R4C is frankly terrible. The 12 volt regulated power supply is an incredibly BAD design. Drake had this 'thing' about running transistors from the plate B+ supply using huge dropping resistors and zener diodes. The above causes an inordinate amount of heat to be generated. Regarding the R4C audio amp, it is reminiscent of a 60's car radio what with its class A output stage. Ex- cept for some cost savings it was an unnecessary design and using the SPR-4 as an example, Drake knew better.
Drake Mods (09 Nov, 1996) 19
Given all these things to be said about an R4C, why would anyone want one? It depends if the C in question is loaded or not. The stock audio and power supply is offensive from a design aspect, but it does work. The transformation of the receiver with decent filtering is phenomenal. What really happened to the C is that Drake cut costs and left the underlying receiver alone. That receiver base is extremely strong but the strengths are buried by the cost cutting. Aside from nostalgia what makes this equipment attractive is that it works, works well, is reliable and of high quality. The AGC on most of the receivers is superior to most foreign equipment. Considerable thought went into its design. It is overbuilt - you cannot break this equipment through age or use. While it may not have been built with the intent for it to still be working 20 years later, most of the Drakes I've seen have had a minimum of repair. All 'old' equipment suffers some abuse as it trades from hand to hand. Surprisingly, the Drake equipment seems to survive at the same level as Collins. Rarely is it butchered and then usually this happens from an inexperienced person attempting repair. Amongst Drake receivers a stock B is vastly superior to a stock C. Some folks insist on having a late model C - "high serial number" without perhaps knowing what they're asking for and willing to pay a premium for. Fine, if you're a collector. They don't even care what options its got, yet if you were to filter up a C and find a noise blanker, it will cost more than the radio. The strange thing is all that stock C's have is not much more than 'potential'. All work pretty well the same. The B requires no work at all and can be had for a song, but don't expect to wade through a pile up on 20 SSB with a B - it can't do it, at least not very well. The B represents balance. It comes from a period where commercially available, cost effective crystal filters where yet to be widely available. If you're inclined to have a B after reading this, I'm flattered - its an excellent receiver, but it is not Excalibur. The C receiver is an incredibly good receiver, but ONLY if it is loaded up with filters. The International filters are better than the filters that Drake supplied. The recovered audio on a stock R4C receiver is quite bad without some change. Just changing the value of 1 capacitor makes a considerable improvement. Once loaded up, the R4C becomes a real DX receiver and can 'slice and dice' with the best. The only way to over- load a properly set up R4C is to connect the antenna terminal directly to the transmitter, its that good. In stock form, you'd have no idea what is there.
1.3.1 R4C Evolution ____________________ The information contained here is accurate but not necessarily a com- plete dossier on the R4C as it changed over the years. Updates will be made to this section as additional information is acquired. o R4C ser no above 16121 Drake Mods (09 Nov, 1996) 20
Revision date - Feb 1973
All mixer tubes 6HS6. First and 3rd mixers cathode injected. Second mixer is a dual gate MOSFET. The IF chain following the first crys- tal filter is 6BA6 1st IF, Noise blanker and then 2nd mixer. 4 posi- tion filter select. o R4C ser no above 18726 Revision date - March 1974 All mixer tubes 6HS6. First and 3rd mixers cathode injected. Second mixer is a 6BE6 with an JFET (2N5459) buffer. 5 position crystal filter selection. 3 diodes in series across the S Meter to compress the meter range. 2 S Meter zero pots were employed - one internal and one external. o R4C ser no above 21000 Revision date - Nov 1974 All mixer tubes 6EH7. First and 3rd mixers grid injected. Second mixer is a 6BE6 with an JFET (2N5459) buffer. 5 position crystal filter selection. Some intermediate models in this transition period may not have installed the new tapped IF transformer, T7C. Amongst the 3 series known, Drake spent considerable effort changing the mixers with particular interest in the IF chain following the 1st crys- tal filter. While no direct measurements have been taken, there appears to be little discernible difference between the first in this list and the latter. As can be expected, it is considered that the later model is superior to the early model. There is a natural tendency to want to believe that this is true, but practical application does not seem to back this up. One of the attractions for some enthusiasts is the vaccuum tube process- ing of the RF signal in the belief that the early model dual gate MOSFET is automatically inferior. The fact that all models in the later series have an JFET in the RF chain is somehow strangely irrelevent to this position. Additional changes can be made to the audio and power supply if neces- sary. Most other changes are subtle and amount to 'busy work' unless there is a specific problem to address.
1.3.2 Sources of Mods ______________________ A number of sources did exist for mods to this equipment. Amateurs like to change equipment around. If the equipment is popular, it is not un- usual for a cottage industry to develop for some enhancements and goodies. Consider the following as reference only: Drake Mods (09 Nov, 1996) 21
Sartori offered for sale a number of accessories for the R4C and TR7 including solid state tubes (a 6BA6 was called a SBA6), crystal fil- ters, audio low pass filters and such. Most notable from Sartori was a killer 16 pole 1.8 kHz SSB filter for the R4C. o Sherwood Engineering Similar to the above, they provided R4C rework services and crystal filters. This company is still alive and very well. I doubt if they have any Drake accessories left on a dusty shelf. Sherwood Engineer- ing has a reputation for quality, well thought out solutions to communications problems. o Fox Tango Fox Tango was bought out by International in the early 90's. F/T originally was noted for their Yaesu FT101 filters and first mixer kit changes. Regarding the Drake R4C, they offered add-ons known as GUF-1, GUF-2 and GUD. The first 2 were filters replacements for the first IF crystal filter in the Drake R4C and were for SSB and CW respectively. The GUF-1 came in 8 and 6 kHz bandwidths. The GUD was a solid state product detector kit replacement. o International Radio This company deals in after market crystal filters for a number of radios. The filters are about $110 and are good. Their filters for the Japanese radios are better than factory and much cheaper. It is difficult to find a better filter for a radio than from these folks. Most of their filters for all of the radios that you could buy for are drop in replacements.
1.4 SOME NOTES ON RECEIVER GAIN AND AGC ________________________________________ Periodically you will read concern regarding 'gain balance' in a receiver and how mucking with the blanker gain, for example, can upset the gain balance in the receiver. It is a concern. One should not con- fuse gain with sensitivity. Although both are related, a sensitive receiver is noted for high gain and low internally generated noise. Once the receiver is sensitive enough to increase its white noise on pre- selector peaking more gain just makes the noise louder, but the ratio of noise increase will remain much the same. The various RF stages that comprise a receiver (RF amp, mixers and IF) act as a unit. Each stage acts as a signal conditioner as the desired and undesired signals are amplified and filtered prior to detection. With a properly designed receiver, increasing the gain in one unique area through modification Drake Mods (09 Nov, 1996) 22
ultimately affects the AGC'd stages since they are part of this entire loop. One typically mistakes a higher S meter reading after modification to mean 'more sensitivity'. This quite often is the receiver attempting to compensate through the AGC. With the AGC now more active on weaker signals and with the different AGC characteristics of the vaccuum tubes now receiving AGC sooner than designed, the receiver is actually now partially shut down. AGC is very important in a receiver. Factors that affect AGC performance are loop gain, hysteresis, decay time and filtering. Close inspection of the R4 series receivers will reveal use of vaccuum tubes with different Gm curves (sharp and remote cut off) and different AGC filter time con- stants to each section. This accounts for the excellent AGC charac- teristics of the receivers. If one dives into this equipment making mods 'for more RF gain' or 're- duce the AGC pumping with sharp filters', these AGC relationships in the receiver as a whole get skewered and your Drake will not be any better. Neither will it sound like a Drake anymore. While almost any AGC is bet- ter than no AGC, excellent AGC requires attention to detail. The results are worth the design and R&D effort. For fun, place an R4B next to any mid priced foreign transceiver and try an A/B comparison. Now, an R4B cannot compete in the selectivity sweepstakes against a radio 20 odd years younger (some things should be better, huh?), but have a listen to what the B sounds like and watch/hear the AGC do its thing. If you listen carefully you can hear the AGC recover and the receiver open up and recover from a strong SSB or CW signal. It actually 'breathes'. This is good, well engineered AGC. ____
1.4.1 R4B and R4C Mods and Tech ________________________________ I've had a few folks ask me which is the most desirable Drake receiver? Well, it depends. First, its a personal item and therefore open for de- bate. I've had folks from various backgrounds provide personal reasons for the R4 A, B and C. For reasons that are contained within this document, I prefer the B or the early model C - the one with the MOSFET mixer. o Voltage Regulation Early R4C receivers employed a 12 VAC secondary power transformer. Later model R4C used a 14 volt power supply by changing the power transformer. The early model supplies could fall out of low limit spec with marginal 110 VAC. While there is a Drake fix for this, the best option is to use an LM380 and lighten the power supply load. o R4B/early R4C LO Injection
Drake Mods (09 Nov, 1996) 23
R4Bs injected the LO into the first mixer into the cathode from a low impedance link on T4. You can improve transceive injection from the transmitter and reduce spurs on 15 and 10 by replacing R7 with a 470 ohm resistor and bypassing it with a .005 uF cap. Run the in- jection to the grid of V2 pin 1 through a 10 pf capacitor from the high side of the small coil on the bandswitch associated with T4 (essentially the switch selector finger). Realignment of the front end is required after this change. o R4B Manual Trivia The front cover depicts the operation of the noise blanker. o Low TX output in Transceive This may also show up as low(er) sensitivity of the receiver when transceived with the transmitter (B and C series). The cause is usually alignment or the injection cables. All RF cables (the C se- ries had 2) must be RG/62 low capacitance cable. It is best to align the receiver and the transmitter when slaved together. o T4any/R4any Intermitent Transceive Sometimes the crystal/VFO switch on the side of the R4B can become faulty. In most cases it is left in the VFO position 'forever' and is easily overlooked. As a matter of course, it should be cleaned and cycled a few times. Pay some attention to the quality of the female RCA jacks on the back of the receiver and transmitter. Quite often these connectors no longer make firm contact with the cables due to wear or abuse. Make sure that the center pin of the interconnect pin is pinched by the socket. In some other cases, you may find that the outside ring of the cable is similarly loose. Cable quality may also be a factor, especially if you are using the original cables. Remember - in most cases you are using cables that are about 20 years old. o R4C Audio (all series) Change C100 from .22 uF to .68 uF. Do not use a higher value. This will remove a lot of the raspy audio and clean up a fair bit of dis- tortion. Use a tantalum and observe polarity. o R4C Pass Band Bleed Through Replace first IF crystal filter with 8 kHz GUF-1. HIGHLY recom- mended. The stock Drake filter is 4 pole with 65 db stopband and a very poor shape factor. The replacement International filter has a stop band greater than 80 db and a good shape factor. This one sim- ple change will improve the receiver considerably. Drake Mods (09 Nov, 1996) 24
A stock R4C came with 2 crystal filters - an 8 kHz wide first IF and a 2.4 kHz second IF SSB filter. The first IF filter does not do the R4C justice. Replace this filter with the GUF-1 if at all possible. You can add a sharper SSB filter. I use 2.1 kHz. Why not a 1.8? Well, the 2.1 has nice 6/60 db figures. It puts up a nice flat band- width plateau without killing fidelity. For CW, a 250 Hz width is about right. The 125 Hz is just a bit too narrow and the 500 Hz is too wide for current band conditions. The 125 Hz makes the tuning and PBT control somewhat touchy. It rings surprisingly little and is a good CW filter. The 250 Hz is not all that much different except that the tuning requirements are more relaxed. Contact: International Radio, 3804 South US Hwy 1, Fort Pierce, FL 34982 407-489-0956 (TU-FR, 13:00 - 17:00 HRS) o Crystal Filters - Tech - TR4 et al These are 500 ohm 9 MHz filters. The TR4any are single conver- sion transceivers. A dedicated SSB filter is used for USB and LSB, although either filter may be used depending upon the band. The reason for two filters is to not have the transmit frequency shift between the sideband selection. - R4C The first IF crystal filter is 5645 kHz at 500 ohms. The second IF frequency is 5695 at 50 ohms. - TR7/R7 The crystal filters are 5645 at 50 ohms. For this reason, you can't put in the R4C first IF crystal filter into a TR7 for an AM filter. It would of been so nice if the TR7 etc took R4C crystal filters, but noooooooo. It looks like this was purposely done in the TR7. The PTO/frequency on this radio is not inverted ala R4any and the lower band edge corresponds to 5.05 MHz on the PTO. The TR7 PTO is essentially the same PTO used in the C line. o R4C S Meter Balance (early model) Some early R4C receivers could not balance the S meter after prop- erly setting the AGC threshold (sensitivity control). Early model R4C receivers have only one trim pot for setting the S meter zero. Replace R33, a 470 ohm 1/4 watt with 680 ohm 1/4 watt. Drake Mods (09 Nov, 1996) 25
The sensitivity adjustment affects S meter balance and sensitivity. Ensure it is no higher than -1.35 volts and no lower than -1.2. o BFO Bleed through R4C Early models could deflect the S meter while the passband tuning was moved across the IF frequency. Ensure all tube shields are in place. In extreme cases, check wiring harness layout and add a 47K 1/8 or 1/4 watt resistor from the base of Q5 to ground. o R4C Intermitent Crystal Calibrator The mounting screws for the blanker brackets are held by two #4 sheet metal screws from underneath the chassis. One of these is a short screw. Ensure that this screw is positioned for the plate near the chassis edge towards the back of the receiver. A normal length screw will short the calibrator when the calibrator is seated down. o R4C T7C IF Transformer The purpose of tapping the IF transformer from the output of the third mixer is to provide gain compensation for the higher insertion loss of narrower filters. You'll notice a difference in the S meter reading of the calibrator should you have another SSB filter in- stalled in one of the CW positions. The S meter will increase in reading when this filter is selected. The difference could be as much as 20 db indicated. While it may be annoying, it is not an indication of reduced sensitivity so long as you can get a noise peak from the preselector as outlined further in the text. o 50 kHz filter (late model) Seems to be applicable to serial nos 21000 and higher. Make a a 50 kHz network of a 10 mH choke and 1000 pf capacitor in parallel. Add a .01 uF 250 volt cap in series with one end. Install this network from pin 5 of V6 to ground. The receiver in question should have a T7C (not a T7 IF can). Lead dress for this mod can be critical and is noted by an increase in audio hash and hum. This change is applicable ONLY to R4C receivers that feed B+ to the plate of the 3rd mixer through the notch filter. My own experience is that this change seems to do little, but it does no harm either. Its a very popular 'secret mod' that you may want to try, just for the hell of it. o 50 kHz IF Coax (late model, early series) Late model R4C (tapped IF transformer T7C) could have some addi- tional CW crystal filter loss due to use of high capacitance Drake Mods (09 Nov, 1996) 26
shielded cable running from T7C. Replace this audio cable with RG/174 and change the value of C49 to 430 pf. You don't need this change if there is no CW filter installed in the radio. Your receiver is eligible for this change IF you have a T7C (NOT a T7) IF transformer and if C49 is currently 390 pf in your ra- dio. In this case, the coax in question will have a slightly larger diameter than the replacement RG/174 and will have a white colored center conductor. o R4C Audio (all) The audio stage in all R4C receivers is terrible. It is a lousy de- sign to deploy in a communications receiver. It causes a lot of heat to be generated, distorts, and has terrible frequency response. There really isn't much you can do about this except substitute an LM380 for the whole damn thing. Connect the output from the LM380 to the earphone jack. When connected here, the anti-vox will still work. The LM380 could be mounted on one of the support brackets for the noise blanker or, if you build a circuit board for it and use ground lugs ala Drake, you could use the 2 audio output transistor mounting screw holes. Some folks have used the LM383 and this chip will provide a bit more audio output. Sartori offered a conversion kit using this chip. I have no personal experience with this chip, but I've heard that it can be tricky to deploy without having it oscillate. o Sartori Passive L/C Filter Sartori provided an L/C filter that was inserted between the volume control wiper arm and the input of the audio amp ostensibly to cure 3rd mixer noise and audio amp frequency response. I had one in an R4C that I had purchased and I removed it. I didn't like what it did to the recovered audio at all. If your receiver has this after mar- ket change, you may wish to make some of the changes - particularly the C100 value change if your receiver is stock. Bypass the Sartori audio filter and see which you prefer. o Power Supply - R4C This is another extreme R4C weakness. It is an incredibly poor de- sign. The 2 resistors at the right hand edge of the board get very hot and will eventually cook the circuit board. One of these is the dropping resistor from B+ 150 for the PTO(!) Drake does this all the time in their equipment and it is a terrible design philosophy. You cannot properly fix the power supply unless you make the audio changes because the class A audio output stage draws 1/2 amp (!!) and hauls the power supply down. Once you replace the audio stage, the low voltage supply will climb and you are strongly advised to Drake Mods (09 Nov, 1996) 27
install an LM7812 regulator in place of the pass transistor at the same time. Once you have made the audio amp AND regulator change, eliminate some of the heat generated from the PTO dropping resistor by power- ing the PTO from the low voltage 12/14 line instead of the 150 volt line. The PTO already has a series 100 ohm 1/2 watt dropping resis- tor so .... no problem to run with the 7812 regulator. There is another mod circulating that uses the filament supply as a voltage boost for the low voltage line. Do not do this mod and if your receiver has had this change I strongly recommend you remove it and revert the supply to original. This mod cures nothing and actu- ally generates as much, if not more, heat. What it was supposed to have done was raise the input voltage above the 7812 input threshold so the regulator can work with the 1/2 amp load of the stock audio amp. While this does work and does reduce hum and noise consid- erably, it also creates a lot of additional heat from the regulator. o Accessory Crystals Band crystals for the Drake and just about any other radio ever made may be purchased from: LesMith Crystals Ltd. (905)-844-4505 These folks do small - read single - quantities and have his- torically dealt with amateurs since Day 1. They offer a high quality product at a reasonable price (abt $17 Cdn). Crystal specs are series, 20 pf and HC6/U for band tuning. You can also use the crystal positions for fixed frequency operation, but this would most likely be used for MARS etc and I won't bother with detail. The crystal specs are different between these two appli- cations. The TR4any uses overtone crystals. Band range crystals are interchangeable between the entire R4any and T4any and even between the receiver and transmitter. o CW Operation If you intend on operating the 4 line on CW only, service life of the 6JB6 finals may be extended by turning the idle bias down to the point that the PA cathode current meter just moves. Please do not run SSB at this setting. Be a pal. o 160 Meter Operation 160 meters on the R4any/T4any was an option and enabled through installation of a 12.6 or 12.9 MHz crystal. The crystal to use de- pends on operator preference. It all depends where you want the band Drake Mods (09 Nov, 1996) 28
edge and what you want the frequency readout to display. If you want '8' to indicate 1.8 MHz, use the 12.6; if you want the band edge to be '0', use the 12.9. Some R4any that allow for 160 operation may have either the 12.6 or the 12.9 installed - I've seen both. If your R4 and T4 both included 160 but use different 160 meter crystals, it can really hurt the brain when slaved until you get used to it. o AGC Transients R4C (early model) Verify that there is a network of a .01 uF and 1 Meg ohm resistor connected in series installed on the AGC board between the wire con- nect points on the board. This network is installed between the green/white wire and the yellow/white wire on the foil side. o AGC Pumping With Sharp Filters When good shape factor crystal filters are employed the AGC will pump when the calibrator is tuned right on the filter edge and the AGC is set to 'fast'. Excerpt July, 1976 Ham Radio pg 12: ".... designs with shape factors between 1.4:1 and 1.2:1 have two unpleasant side effects: 1. The extremely sharp skirt selectivity presents a problem for the AGC circuit because of high group delay and phase shift, which cannot be compensated for. In almost all cases strong inter- fering signals at the edges of the filter response band will make the AGC pump. This instability introduces distortion and overshoot. 2. Because of their high Q and ... the filters ring." Continuing, Rohde says ".... SSB reception should be between 1.9 and 2.4 kHz to limit operator fatigue .... (The) bandwidth on the famous KWM-2 was restricted to 2.1 kHz for this reason." Ignore it. You can't fix this without hurting the otherwise wonder- ful AGC. Many theory books show 'ideal' filter passband as an oblong box on its edge. This is not inaccurate when confined to desirable IF bandpass characteristics. 'Practical' filters have skirts. Some fil- ters with sharp skirts will not cause severe AGC pumping but they may have quite severe ripple, depending on the response type. In general, the 90's approach is for large stopband attenuation and filter shape factors of around 2:1. IF DSP can clean up the skirt problem. This is overkill for Amateur applications, but does illus- trate the move away from 1980-think of severe skirt roll off being desirable. There will always be trade offs. Drake Mods (09 Nov, 1996) 29
Amateur 're-engineers' have claimed that an R4C weakness is 3rd mixer noise. Some of these amateur engineers have had a considerable 'go' at the third mixer inventing theoretical problems that gener- ally do not exist. It is the 1st mixer that sets the sensitivity of the receiver. It is the third IF amp that provides a significant amount of the receiver gain. By the time the signal gets to the 3rd mixer it should be pro- cessed enough to easily overcome 3rd mixer noise. And it does. If your receiver works well, leave the 3rd mixer alone. Drake employed considerable changes over the years to this area throughout the R4C series. Improvement in an early R4C can be ren- dered by installing a pair of back to back diodes from the junction of C53 and C52 to ground. Use 1N4148. When Drake employed the 6EH7s as mixers, the injection was moved from the cathode of the 3rd mixer to the control grid. It is this connection that some Drake enthusiasts assume to be 'noisier'. This connect point isn't 'noisier' (white noise). It *is* very capable of creating hash and is much less tolerant of sloppy lead dress. I have a mod for this further on with much greater detail. There was also a Sartori mod that injected the LO signal into the third mixer from the bottom end of the secondary of the 3rd mixer grid input transformer. This mod follows good engineering practices and one of my R4C receivers has had this change. My other R4C, an early one, has the injection to the cathode of the 6HS6. I cannot tell much difference. o R4C Noise Blanker Do not use the blanker gain trim pot to make the receiver 'more sensitive'. It won't. Ensure the S meter deflection on the calibrator is exactly the same on 10 meters both with the blanker and with the 9 pin jumper plug. Excessive blanker gain will degrade the AGC by compromising the gain balance in the receiver and possi- bly allow the BFO to bleed into the IF strip. o Blue Dial Filters The heat from the dial lamps will eventually turn the blue dial and meter filters clear. You can restore the color by dipping the bulbs in nail polish, specifically Artmatic USA #163 Peacock Blue Nail Enamel (With Hardener) (Dec 1993 QST pg 86, A. Ross W2NXC). o R4C IF and RF Amp Resistor Changes There have been previously published mods to change screen grid resistor values to improve sensitivity and allow for S Meter zero on early R4C receivers. This is a bad mod. It does not improve sensi- tivity and is overkill as a method for S meter balance. It increases Drake Mods (09 Nov, 1996) 30
the receiver gain and consequently alters the good AGC charac- teristics of the receiver. Do not do this mod and if your receiver has been modified, revert to original factory values. o R4C Late Model 3rd Mixer As explained above, this 'flavour' of R4C with the 6EH7 3rd mixer is claimed to be noisier. Well, it isn't noisier. My late model R4C was not original in this area; it had been modified to inject the LO through the bottom of T6 into G1 of V6. It worked well, but there was a lot of hash - power supply 120 Hz spikes in the audio. When I placed a screw driver blade near G1 (or C199) of the 6EH7, the gar- bage increased. This is no good. No good at all. The following will not cure white noise in the 3rd mixer, but if you have the above problems, it will kill this hash, buzz and assorted garbage once and for all. All mixers make white noise - consider it uncurable. Basically, this mod changes the 3rd mixer to cathode in- jection and allows G1 to be DC grounded. The verbal text describes the end result of the circuit changes and is not a step by step procedure. Change CR20 and CR21 to 1N4148. Change C52 to .005 uF. Remove C200 and C199. Replace C199 with a straight piece of wire. Where C52 con- nected to pin 1 of V6, connect it to pin 3. This essentially reverts the 3rd mixer of late model R4C with the 6EH7 to the circuit used in the early models. I cannot give you a before and after comparison, for I never have had a chance to play with a stock late model R4C. However, after this mod my '6EH7' R4C is dead quiet with the stock audio amp and power supply. With no antenna and normal volume I'd swear the speaker was disconnected. Additionally, the problem with the S meter moving as the PBT control was rotated was all but eliminated. Signals literally jump out of the speaker from nowhere. This change will not make the receiver more sensitive, but it did clean up significantly the garbage in the audio (for me). The reason for this change revolves around the need for a DC path for G1; cathode in- jecting the LO is the easiest way of provide injection. Addi- tionally, the concept is proven from the earlier R4C designs. Indications are that the 6EH7 is a pretty 'hot' pentode mixer. I cannot testify to what an original late model R4C was like. Before you try this change, I'd expect that you have some audio hash that gets almost unbearable in the AM position. When you place a screw- driver near C199, the hash and 'junk' increases in amplitude. If you do not suffer these symptoms than rule 1 of modifications takes precedence .... "If it ain't broke, don't fix it." o R4C Audio Hash
Drake Mods (09 Nov, 1996) 31
R4C receivers are notorious for making not only horrible audio, but also having some hum and power supply hash thrown in for good meas- ure. Most of this is curable, but not without some effort. The later model using the 6EH7 3rd mixer is the worst of the lot. Noticeable improvement can be made by returning the power supply secondary grounds to the canned filter caps. Some folks have put a copper strap under the circuit board ground lugs on the circuit boards, running a strip of copper under the whole length, grounding the lugs. I'm skeptical about the long term. Copper corrodes. The low voltage supply/regulator/audio is marginal, at best. Measure the voltage on the audio output transistor emitter. If its above about .5 volt (assuming the proper emitter resistor), the transistor could be drawing too much current or be going into thermal runaway, hauling that marginal supply down. The previously listed mod changing the 3rd mixer 6EH7 to cathode in- jection helps considerably, for it grounds G1 to DC. This (original) floating grid can be responsible for an incredible amount of crud. For a simple solution to the inherently lousy audio response in the stock audio amp, the C100 change makes it much more pleasant. For the price this receiver sold for, it shouldn't have these prob- lems in the first place. What makes it worthwhile is how good the receiver becomes once these marginal and frankly unacceptable characteristics are attended to. o R4B Sensitivity Tune in the calibrator and then pull V10, the 12AX7 noise blanker clamp. If the S meter rises, replace the tube. A gassy 12AX7 will drive the NB clamp diode partially on, killing IF gain. If a new 12AX7 still does not cure the problem, it could be caused by the clamp diode. An acceptable substitute is a 1N270. o R4B Crystal Filter An R4C first crystal filter can be used if T5 and T6 in the R4B are replaced with R4C part number 251-9285. The filter would be in- stalled on the preselector bracket and coax run from the low impedance windings of the replacement transformer to the filter. T6 in the R4B is part of the crystal filter. There would be some sheet metal work involved for brackets and shielding to insure that the filter stop band attenuation was not compromised. You'd do this if you were to purchase a GUF-1 for your beloved R4B.
Drake Mods (09 Nov, 1996) 32
1.5 T4 SERIES TRANSMITTERS ___________________________ All of the Drake 4 line will transceive amongst themselves. Between the T4X and the T4C there was little difference. Most of the changes in the T4C from even the T4X were cosmetic or for better operator convenience. The B series used neon bulbs to indicate the active PTO when set up for transceive; the C line turned the dial lights on and off. A properly working T4any will give about 150 watts output on 80 meters, dropping to 40 or 50 watts on 10. The audio should be really clean and with properly operating ALC you should not be able overdrive the finals. There should be LOTS of drive on all bands.
1.5.1 T4 Evolution ___________________ The T4X and the T4B differ very little, except mostly in the PTO dial plates. The T4C functionally was not much different from the T4B, except in areas of operator convenience. The T4C is noted for the following ma- jor differences: o Separate BFO Line o FETs in the BFO oscillator o Different method of ALC detection o VOX on/off from front panel o Controls moved to back of set o Dual concentric PTO dial plates o Plain chassis o Meter switch activated by pushing LOAD control shaft o Active PTO indication by dial light o Blank RCA jack holes for VHF transverter drive kit o Separate VOX delay controls for SSB and CW
1.5.2 T4any Mods and Tech __________________________ o Can't Tune 10 Meter Driver Plate
Drake Mods (09 Nov, 1996) 33
This is characteristic of 'generic' 6JB6 tubes. Replace with Sylvania 6JB6. Problem caused by high input capacitance of tube(s). o VOX Gain - T4X and T4B In cases where more VOX gain is required pick up the VOX input from the mic gain control instead of from the plate of V9b pin 6. When re-routing the audio pickup point, bypass pin 6 with a .05 uF cap. o T4C TX Lock up Lock up on a T4C is usually caused by a gassy mixer or 12BY7 driver tube. Other causes include leakage either to ground or B+ of the TX keyed line. This is a high impedance line. In extreme cases the cause can be T6. Inside T6 is a rubber washer that can contact the coil pins internally. The fix is to remove T6 and the shield and in- stall a fish paper washer between the bottom of the rubber washer and the bottom of the transformer base. o T4C Side Tone - Elimination Standby CW sidetone may be eliminated by placing a 22 Meg ohm resis- tor between the pin in the centre of the circuit board in front of V7 (the one with the wire going to pin 1 of V7) and the lug at the top left of the board (the one with the 150K resistor). o Substitute VOX relay tube A 6AQ8 will replace the 6EV7 if a 47 ohm 2 watt resistor is added across pins 4 and 5 of V10. The tube change is applicable across the entire 4 line (and TR3). The resistor IS NOT needed in any of the transceivers. Just swap the tube, in this case. o Fan The PA cage area gets quite hot when in use and some forced air cooling is desirable. The easiest way of accomplishing this is to use a small 1 1/2" 12 volt DC fan. Mount the fan on the outside of the PA cage through the perf holes on the back of the PA cage. Power the fan from a half wave rectifier filtered with about 100 uF de- rived from the 12 volt filament supply. Route the fan wires through a chassis hole along back top of the chassis. The rectifier can be connected between the filament fuse and an insulated standoff. This mod can be done without drilling any holes or destroying the units originality. Orient the fan to blow in. These types of fans are CPU coolers and can be bought for less than $10. They do not move a lot of air and move even less through the perf holes. What is necessary is not cooling, but circulation, and this simple expedient helps a lot. This mod will greatly extend the service life of the 6JB6 tubes at the expense of faster accumulating radio dust bunnies. Drake Mods (09 Nov, 1996) 34
1.6 T4 RECITER _______________ This is a T4X with the PTO and crystal deck removed. It was intended to provide a transmit function in conjunction with the R4A and R4B receiv- ers. The only other similar device that I know of is the Atlas 210 se- ries. A similar series of devices was the Atlas RX-110 receiver and TX-110 transmitter. The TX-110 used the VFO signal of the receiver in a way similar to the Drake R4B/T4 Reciter combination. Obviously, the Reciter is duplicated whenever you slave a separate T4any completely to the receiver. I've never seen one. This is an item for the curious or the collector and may sell for either next to nothing or might demand a high price from its 'rare' nature. For the practical, and with the used Drake 4 line so readily available, it does not serve much of a purpose other than its novelty value. Any modifications or service notes that gener- ally apply to the Drake T4 series transmitters would apply to this unit.
1.7 TR3 TRANSCEIVER (CIRCA 1963) _________________________________ This transceiver is best described as a 'sleeper'. It is a 5 band SSB transceiver that predated the TR4, placing it in the mid 60's. Most of the units available are pretty weatherbeaten, but I have seen one or two that were in beautiful shape. All of them are relatively inexpensive. If you want a nice, inexpensive glassFET transceiver, a TR3 is hard to beat. They work as well as a TR4 and look very much like one. I doubt if you'd mistake the two, but if you did, little harm would be done. The TR3 has styling similar to a T4X, the precursor to the T4B. As is not unusual for the Drake transceivers, most of what is mentioned for the TR4 is applicable for the TR3. Make sure you get the manual with the radio! Basic differences to the TR4: o 12JB6 tubes in the PA (3) o Vaccuum tube PTO o No rel output indication o No CW sidetone o No CW filter o IF Filtering not as sharp as the TR4 o No provision for a blanker Drake Mods (09 Nov, 1996) 35
If all you wanted was a TR4 to play retro radio with, a good clean TR3 would do almost as well and can be had for a song. Be careful in this area. Radios this old will suffer from use, and pay careful attention to the switches, controls and the operation of the two meters.
1.8 RV3 AND RV4 REMOTE VFOS ____________________________ These units are functionally compatible to both the TR3 and 4. To have the RV4 work with TR3 only a minor change is required. Both units use a 12AU7 in the buffer stage. The RV3 uses a 6AU6 for the oscillator; the RV4 is solid state using an FET. The RV4C uses the dual dial plates com- mon to all the C line and the SPR4. The RV3 will work with the TR4any, but the RV4 will not work with the TR3 unless the TR3 is modified. On the remote VFO plug on the TR3, cut the jumper wire running between pin 2 and 8. If in the future you remove the remote VFO, you must restore the jumper or make up a dummy plug from a Cinch Jones connector.
1.9 TR4ANY TRANSCEIVERS ________________________ The TR4 series represent possibly the BEST vaccuum tube transceivers ever made. The transceiver will easily put out 200 watts on 80 meters and 100 watts on 10. For comparison purposes, the unit is somewhat SB100 series like, but the TR4 receiver is much more sensitive on 15 and 10. Unlike the Heathkit, a noise blanker could be installed. It was only the very last TR4 that had an RIT circuit. The TR4Cany had a plug in relay; on the TR4, the relay was open frame and hard wired. All TR4 have a 9 MHz IF that is incompatible with other C line. They will not transceive with an R4any, but they will mute and T/R switch the antenna line. Because a 9 MHz IF and a 5 MHz VFO is used, 20 meters is generated 'free' but tunes backwards as a consequence. If you suspect the crystal oscillator having a fault, check for output on 20 or 80. The TR4 had full 10 meter coverage; on the TR4Cany only 28.5 was in- cluded - the other 2 band crystals were options. There were 4 different series of transceivers that I am aware of: o TR4 (circa 1970) The basic transceiver. No RIT or CW filter. The AGC characteristics in the TR4 are 'better' than any other transceiver in the 4 line, but the differences are subtle. After Drake Mods (09 Nov, 1996) 36
this model, Drake made some subtle changes in the AGC amplifier, V13. Full 10 meter coverage. o TR4C The basic C transceiver. No RIT or CW filter. Dual dial plates. Some minor changes in the tube line up and 1 pf caps on the IF transfor- mers to get some more gain. The audio output stage in this and subsequent models employed negative feedback. Basically a plain TR4 with C line PTO. o TR4Cw Some subtle internal changes. Dual dial plates. Has a 500 Hz CW fil- ter. No RIT. Basically a TR4 but with the C style PTO dial plates and a CW filter. o TR4Cw-RIT The final model, sold for a period of time against the TR7. This model had it all - CW filter and RIT. It is distinguished by having the RIT control positioned in the lower right hand corner where the NB switch resided and having 2 pushbuttons in the lower center of the front panel for activation of the NB and the RIT. The TR7 uses a very similar RIT circuit. Over the years, the TR4 didn't change all that much. All models are noted for high TX output, sensitive receivers and for running hot. You need a fan. Most of the TR4any I see do not have the noise blanker. Pity. The 34PNB works very well. Typical for a transceiver of that era, there is no selectivity available other than the SSB crystal filter (or the CW fil- ter, depending upon vintage). Just about any flavor of a TR4 will serve you well on sideband, but to get the RIT function, you need to purchase a TR4Cw-RIT or have a remote VFO. In this day and age, RIT is not as important as it was, for the people you are most likely to work will be more stable than you are. It is *they* that will be using RIT. The DC3 or DC4 will allow the TR3 or TR4 to go mobile, but the radio is just too big for most modern cars. There is no reason why you cannot operate one mobile, but you'll need a mindset for installation that goes beyond con- necting a 2 wire 12 volt cable to the back of the radio. The filaments alone consume as much power as a Scout puts out. It is possible to install an RIT circuit into the earlier model series transceivers by duplicating the Drake RIT circuit. Your greatest chal- lenge will be to add in the appropriate controls without butchering the front panel, unless you don't care about it. Within 10 ms of taking your Black and Decker to the front panel, that TR4 of yours is worth .... nothing. You cannot make a homebrew RIT by rubbering the band crystals because 80 and 20 do not use band crystals. An alternative RIT is to find an RV4 or RC4. The chance of finding a TR4Cw-RIT is real slim and expect to pay if you find one. It is not too practical to attempt to Drake Mods (09 Nov, 1996) 37
retrofit the CW filter, however, since this requires replacing the sideband switch and building mounting brackets. I have heard that Drake will upgrade a TR4C to a TR4Cw for $105. This is a good deal.
1.9.1 TR4 Mods and Tech ________________________ The changes or mods for this equipment are few. The tube line up changed a bit - different 100 kHz oscillator tubes and such, but for all prac- tical purposes the radios performed about the same. o TR4 Manual Trivia The front cover of the manual depicts the 2 crystal filters in the radio showing the skirt selectivity and bandwidth. o Increase IF Gain The TR4Cw had 1 pf capacitors across the IF transformer hot side (T11 and T12) to increase the IF gain. Since bandwidth is determined by the crystal filter, this had no effect on the receiver. o Different TX and RX Preselector Peaking Especially noticeable on 10 meters, its 'normal'. There is not much you can do about it. o 9 MHz BFO Imagine the passband curves of the two sideband filters together as the capital letter 'M'. The BFO is set dead center in that middle valley between them. Proper setting of the BFO is to listen to the receiver with no antenna and switch the sideband selection, adjust- ing C130 for the same pitch. Sometimes you'll adjust it and 5 min- utes later, the adjustment has drifted. In almost every case, this is caused by C130 losing its temperature characteristics. Two things will cause this - the ceramic has a hairline crack or there is crud in the trimmer. The following is not for the heavy handed .... All of these Centralab trimmers are held together from the bottom by a tripod clip that fits into a ring machined on the roter shaft. Grab the long pin firmly with some needle nose (bottom chassis) and GENTLY pull and push down at the same time. At the same time, push very gently on the tripod clip with a small screwdriver just behind the center of the clip where you see the rotor pin . If you get this just right, the little ceramic disk on the top will fall out as the clip extracts. Don't apply so much force that the trimmer is smashed or, when the clip lets go the pliers run amuck. Drake Mods (09 Nov, 1996) 38
Now, inspect both inside surfaces for cracks. If its cracked, re- place the trimmer. If it looks OK, clean both surfaces with alcohol and a fresh J-Cloth. Don't touch the surfaces! Oil from your fingers will ruin the repair and you'll be punished by having to do this over again. Now put it back together (heh heh). Allow the radio to heat soak for 15 minutes with the top cover on and then adjust C130. I've done this a number of times over the years with these trimmers on various radios (NCX-5, most Heath). Oh yes - NEVER put a pencil mark on the side of these trimmers to indi- cate calibration. Guess where the graphite goes in about 3 months? o C130 TR4Cw and TR4Cw/RIT The adjustment of the above trimmer is somewhat critical for proper CW reception, for the CW filter frequency is specifically designed for the 9 MHz BFO to be precisely on frequency. The sideband balance adjustment of C130 will affect the CW reception of the transceivers - the place where the note peaks to a *very* large degree. Be careful setting this BFO trimmer, for there is a filter match procedure to follow also. Without the filters properly loaded, the BFO adjustment using the 'hiss pitch' will be colored by a poor fil- ter match setup. o AGC Changes/Differences Around V13, Drake made changes after the TR4. It looks like this was done to provide an AGC delay. In the TR4Cany, Drake changed the cathode to B- resistor from 47K to a 43K and a 150 K in parallel. This network computes to about 33K. The change is subtle, but you could remove the 150K resistor, R193. This will make the AGC more 'active'. This parallel network *looks* like a post production change, but don't quote me. o TR4any VOX Delay The TR4any has a fixed VOX delay. There is no adjustment for this delay; it has been set at the factory. The delay is about a second. The manual outlines a simple procedure for setting this delay to other than factory default. In most cases, the delay is about right. o Antenna Fuse Bulb This is located inside the final cage and is a #12 bulb. A #12 is 6 volts at 150 ma - exactly the same as a #47, but with a different base. This bulb is a bit silly, for it will take well over a watt of RF to open it. By then, the receivers ruined anyway, most likely. If you really want this protection (its good Stupid Insurance), pull the bulb and put a Radio Shack peanut bulb (6 V at 50 ma or so) Drake Mods (09 Nov, 1996) 39
across the terminals. The cold resistance of this bulb will not af- fect the receiver adversely. o TR4 Improved RX Audio On the TR4, C212, a .0015 uF on G1 of V17, a 6AQ5, should be paral- leled with a .01 uF 300 volt cap. This will remove a lot of the brassyness and distortion. Following the TR4, Drake made some changes around the audio output stage, but they employed negative feedback to recover the frequency response of the sharp roll off of the coupling cap and grid resistor of V17. o External Antenna Switch The switch on the side of the TR4 allows for an external antenna to be connected. Whenever you move the transceiver, the switch moves to external by mysterious cosmic forces. You connect the antenna and wonder why the receiver is dead. To prevent this, you can lock the switch by placing a 4-40 nut in the exposed slot where the tab slides back and forth. Cover the nut with some tape to prevent it from falling out. o What Happened to 15 Meters? There is no 15 meter adjustments in the radio aside from the band crystal. Make sure you place the preselector where the manual tells you to during alignment of the various bands. If you inspect the bandswitch, you'll see some small air wound coils about 1/4" in diameter. These coils are used for the three 10 meter crystal oscillators and for 15 meters. Now that you know this, that does not give you an excuse to muck with them if you have trouble in these areas. Those coils have sat there for 20 years. If you have trouble in any of these areas in your radio, it will never, ever be with these coils. o Low Sensitivity 40, 15 or 10 Meters First, check for sensitivity on 20 meters. Is it OK? What you've just done is verify that the front end is just fine and that the problem is in the VFO premixer - the 6EA8. Quite often peo- ple will twiddle the transceiver - see "15 Meter Osc Inj" on the coil can and tune for max S meter. This is OK, but they forget that there is a similar slug on the bottom of the coil can too. Of course one slug affects the other. And, again, you needn't bother with the loading network. o Relay Cycling
Drake Mods (09 Nov, 1996) 40
Especially on the transceivers, sometimes when you put the unit in TUNE, it will drop out or cycle as you advance the DRIVE control. Nothing is wrong - its caused by having the RX audio set too high in relation to the anti VOX. Its actually the sidetone signal thats do- ing it. Turn down the audio gain, pull the mic or adjust the antivox. Another cause of relay cycling can be the filter can as mentioned in the general comments section. o Relay Specifications The relay changed from year to year, from open frame to enclosed, depending upon the model of the transceiver, but the relay coil specifications did not. The relay is 120 volt and 15,000 ohm coil. What if I can only find a 120 VAC relay? Measure the resistance and if its 12K to 18K, use it. In most cases, AC relays are the same as the DC relays except for a shorting turn. In all likelyhood you can use one and never notice the difference. o Ventilation All Drake vaccuum tube equipment that transmits should be placed in such a way that adequate air flow is provided. This is especially true for the transceivers. If there is adequate airflow, you'll find Drake equipment to be quite gentle on components. Conversely, if you choke a TR4 off from free air circulation, you'll eventually cook the components. The first to go usually are ceramic disk capacitors. If you have to replace more than one or two of these, it is a sure sign that someone cooked the radio. o Fan The PA cage area gets quite hot when in use and some forced air cooling is desirable. There is quite a lot of heat trapped in that final cage that is trying to escape by convection. The answer is a fan, not so much for cooling, but to help purge the hot air inside the final cage. The only place to mount a fan is on the back of the final cage. A small 12 volt 70 ma 2 1/4" fan just fits nicely. If you route the leads through one of the corner chassis holes, they will come out in the final compartment. You can pick off the 12 VAC from the junction of the feed through and the filament choke. Do not go to the final tube filament pins - they are RF isolated by the chokes. Power the fan from a half wave rectifier filtered with about 100 uF at 20 volt. This mod can be done without drilling any holes or destroying the units originality. Orient the fan to blow in. I use a larger fan on the TR4 than a T4any simply because the TR4 needs some good air movement. With the 2 1/4" fan on the TR4, the unit can be used in- definitely and does not give any signs of doing a mini-Chernoble.
Drake Mods (09 Nov, 1996) 41
Please note that the TR4 is not unique regarding heat. Almost all other radios of this era used convection cooled finals. They too need some forced air cooling or circulation. This is true of all Heathkits (inc HW12 series), Collins, Galaxy - the list is endless. This mod will greatly extend the service life of the 6JB6 tubes. For the most part Drake did a good job designing the chassis for venti- lation. An inspection of the radio from this aspect will reveal thoughtful placement of power resistors and discrete chassis holes. o TR4 Noise Blanker This blanker is very similar to the blanker on the R4C and is simi- larly very effective. Note that there is a different blanker model for TR4 serial numbers before 31321. Quite a few transceivers were sold without noise blankers. As with other Drake accessories, the 34PNB is difficult to find by itself. The R4C noise blanker is unique from an TR4 blanker and cannot be modified to operate in the transceiver for the following basic rea- sons: - Different IF frequency - Different on/off switching - TR4 blanker has bidirectional signal path
1.10 SPR-4 ___________ This all solid state receiver is a essentially a solid state general coverage R4B. It is extremely sensitive and stable. The frequency is 'programmed' by installing the appropriate crystal - one of up to 23 into the sockets behind the band selector switch. There are few weaknesses or vices in this receiver. The AGC design is weird and in certain points, very high impedance. An 11 meg ohm input meter will drag the AGC down. The SPR-4 uses the same PTO and dial plates as the R4C. Some models were specially constructed for the FCC when they cared about the mess on CB and had the CB channels marked on the dial plates in red. It is done in an ingenious way and is fascinating to watch in action. There was an 'early' model SPR-4 and a 'late' model. The exact differ- ences are sketchy at time of writing. One definite difference is in the audio board around the area of the power output transistors. Late model SPR-4 used a pair of EP-487 TO220 transistors. Early model SPR-4 used transistors with unique mounting tabs. The entire boards are inter- changeable and still available in 1996. If you have an early SPR-4 with audio troubles, replace the board. Drake Mods (09 Nov, 1996) 42
1.10.1 SPR-4 Mods and Tech ___________________________ o Sensitivity Measure the input resistance with an ohm meter at the antenna termi- nals on any band but 'A' or 'B'. It should be about 2 ohms. If it is not, likely the ground pin on the input matching coil has become unsoldered. This will be hard to get to and you'll be required to unscrew the slide switch on the back panel immediately above it. For some reason this solder connection seems to fatique over the years; perhaps the area is stressed during assembly. On 40 meters and above an SPR-4 will still 'hear' a lot of signals with the input link coil ungrounded. All thats coupling the antenna in this case is just stray capacitance and is surprisingly adequate. If you have this problem, you'll notice 80 and 160 not to be too perky, yet the receiver aligns OK. o IF alignment The 50 kHz IF transformers tune broadly. The 50 kHz bandpass network coils accessible from the rear chassis panel tune sharply and are critical for proper sensitivity. Align with the bottom plate in place. It isn't easy, but this is the only way to get a good alignment. Do not disturb any of the wiring around this area of the receiver. o AGC The AGC in the SPR-4 is somewhat unique. The AGC controls on the back of the S Meter affect its strong signal performance. The AGC line is very high impedance. You cannot measure it successfully without dragging it down. The board behind the S meter contains the RF amplifier AGC. If you have problems setting up the AGC in exact accordance with the in- structions, replace Q14, the AGC FET amp. The AGC bus goes right to the gate of Q14 - any leakage at all will ruin the AGC. An MPF102 will work fine. o Alignment Tricks Drake wants you to measure the AGC bus during alignment. A voltmeter will drag the bus down. Don't bother - there already is a voltmeter there - the S meter. Use it instead during alignment.
1.11 TR5 _________ There is a natural expectation that incrementing series numbers from a manufacturer imply that the higher number is a later model. In the case Drake Mods (09 Nov, 1996) 43
of Drake HF radios, the TR7 followed the TR4Cw and the TR5 came after the TR7. Despite this, the TR5 is a good interpretation by Drake of a solid state TR4Cw-RIT. There is a marked resemblance of a TR5 to a TR7. Most notable in the TR5 is a digital VFO, although the radio still em- ployed band crystals. The TR5 followed the TR7 and was announced for general market around 1982. It is a ham band only transceiver with a real synthesizer. It could best be described as being similar functionally to an TS-120 or Swan MBX-100. It can also be described rather accurately as being a solid state TR4Cw-RIT. It came with few accessories - there really wasn't all that much to add. It was an SSB and CW transceiver and did not cover the AM and RTTY modes offered in the TR7. The TR5 did include WARC band coverage of the 10, 18 and 24 MHz sub bands. There is no PBT or IF Shift. It could be looked upon as a 'baby TR7' for it is very similar in appearance. Instead of two rows of push buttons on the '7, the '5 has a single row of rocker switches, but the basic layout is much the same. The TR5 also had its 'own' line of accessories, most notably the L75 linear (single 3-500) and RV75 digital remote VFO. The RV75 would of course work with the TR7. The companion power supply, the SP75 will of course work with the TR7. This supply provides an unregulated high cur- rent 12 volts for the transmitter PA and a low current supply for the low level electronics. There is *nothing* wrong with this. Atlas did this too. There is no need to provide a lot of filtering, OR regulation to the PA stage. Drake seems to have tightened up their specifications a bit since the TR7, especially in the area of third order intercept point. The TR7 was rated at +20 dbm at 100 kHz; the TR5 was rated at 0 dbm at 20 kHz. The narrower figure gives a more realistic rating under typical conditions. The QST review of the TR7 in May, 1979 was favorable but sloppily done. The TR7 DOES have an amplifier following the first mixer which is a di- ode DBM. There is an obvious typo rating the 3rd order of the TR7 at 90 db. This is tantamount to saying you can connect the TR7 RF input to the national power grid. I think they meant dynamic range. The TR5 has little to recommend it. The TR4Cany has charisma - the TR5 is just a basic HF transceiver. The TR5 is a little rare and people try to sell them as 'collectors items'. This, it might possibly be some day. Until that happens, it is just a simple, basic transceiver made by a company that no longer makes Ham gear. A TR4Cw-RIT *is* a bit of a col- lectors item. The TR5 is *not*.
1.12 TR7 _________ By the mid 1970's it was obvious that a new generation transceiver was required. Vaccuum tube equipment was being replaced by solid state ra- dios - especially for those that wanted to operate mobile. The solid Drake Mods (09 Nov, 1996) 44
state equipment was obviously the way of the future. Drake answered this challenge with the TR5 and TR7 transceivers. There also was an R7 receiver. This unit is not that common. Yes, there was a TR6. That was a 6 meter SSB transceiver circa 1970 in much the same vein as an SB-110. Yes, there was an 'A' model of the TR7. This is around a 1982 flavor. What the 'A' model of the TR7 and R7 really was all about is that the equipment contained standard such as noise blankers and crystal filters that were options on the earlier model. The TR7, as is common for most Drake equipment, is over built. This is characteristic of most well made American equipment. While a TR7 may not have all of the useless 'features' of foreign equipment, it is as reli- able as a rock and solidly built. Drake made sure it was a quality piece of radio and not intended to be disposable. An example - the TR7 gener- ates 150 watts (250 in or so) output, yet the PA is capable of at least 225 out. At its nominal power rating, the final transistors are under utilized. Most foreign PA stages do not have any where near this headroom. The transceiver is big and heavy at 17.5 lbs despite an aluminium chassis. Glass epoxy boards are employed throughout the radio. The receiver is dead quiet and almost immune to overload. A large part of the reason for this is the lack of an RF amplifier and a strong pas- sive DBM in the front end (ala Atlas 210). The TX SSB audio is rich and clean. The AGC switches with the mode setting for near optimum tailor- ing. The only item to be missed is an IF notch filter. You'd look at a TR7 today perhaps with some distain if you didn't know any better. A TR7 is a classic example of old ham gear easily overlooked since it is 'old tech'. Yet quite a few of the same amateurs will get very excited over a Racal or other piece of 'commercial' equipment. You'll read fur- ther on what a TR7 really represents. You see, Drake just didn't make amateur gear. A well working TR7 is a treat to use. Transmitted audio is excellent and the receiver is a gem. The major downside of the radio is its current requirements. Nominal drain on receive is about 3 A, on transmit, it could run to about 22 to 25 A. Both of these figures are considered slightly excessive today. The size of the radio rules out mobile oper- ation in most of todays cars and the red LED frequency display washes out in sunlight.
1.12.1 TR7A/TR7 differences ____________________________ The TR7A was an early 80's transceiver that had some subtle differences to a TR7. Not that many were made and it is a bit of a collectors item. Practically, it isn't all that much different to a TR7 except in the following areas: o Came with noise blanker Drake Mods (09 Nov, 1996) 45
1.12.2 TR7 Mods and Tech _________________________ I have encountered few mods for this radio. This could be caused by the difficult nature of performing them or by the very fact that a stock TR7 is pretty good as it is. What makes this radio difficult to modify is the plug in board modules. This is good. This means that a TR7 is un- likely to be mucked with too severely. Your worst problem is likely to be alignment if your 'new' TR7 is a little sour. o Servicing A TR7 is a robust transceiver that is almost impossible to kill. It holds its alignment extremely well and generally is overbuilt and 'overdesigned'. Once brought up to specifications, it should stay that way almost indefinitely. However, should your TR7 require service, you are in a bit of a di- lemma. To service a TR7 beyond the superficial, one needs a good oscilloscope, voltmeter, service manual and the extender boards. The latter two are no longer available from Drake. A service manual may be purchased from: Antique Manuals, K7FG 1-800-807-6146 The telephone number is ... interesting. This organization sells manuals for a considerable number of exam- ples of old(er) gear and a lot of BoatAnchors. The current price of the TR7 manual is about $34 US. Its not a bad deal. A TR7 is not difficult to set up, but one must be aware of what to tune and what not to touch. DO NOT align the first crystal filter unless you are prepared to go at it with a sweep generator. Quite a number of slugs, trimmers and trim pots are involved in an alignment and not all of the adjustments are immediately accessible. Especially in the case of a TR7, if it works, don't fix it. Drake Mods (09 Nov, 1996) 46
The outlined procedures in the service manual are very well thought out and are presented in a linear progression. Follow them. The synthesizer set up is a bit tricky. Most important is to ensure that the 40, 13.695 and 8.05 MHz oscillators are exactly on frequency. If each one of these is within 100 Hz, then the readout, PBT and CLAR will 'naturally' fall very close to spec. Proper test equipment is essential to set up a TR7. o All Band Transmit Included with this article are additional TIF and TXT files outlin- ing Drake synthesizer changes for full receive coverage and full frequency coverage transmit. o Digital Display For a while the DR7 digital display was an option. A TR7 is signif- icantly less without the DR7 display. If you are looking at a TR7 to purchase, make sure that it does indeed at least have this option installed. Of all the 'options' available for the TR7, it is un- likely you'll ever find a loose DR7 unless someone is cutting up a TR7 for parts. o Early and Late Models The very early model TR7 was sold without the DR7 board. It is un- likely you will encounter one of these - few were made. ASK if it has digital display before purchase! The early model TR7 had a 3 transistor predriver on the PA heat sink. Additionally, the adjustment for TX/RX frequency required you to remove the DR7 and use extender boards. Very inconvenient. The later model TR7 uses a 2 transistor predriver. You need to pull the top cover and look at the circuit board closest to the front panel. If you see a U shaped aluminium heat sink, it is the later model. Additionally, this model TR7 had an access hole on the motherboard for the TX/RX frequency adjustment. o TR7 Mixing Scheme The TR7 and TR7A is a dual conversion transceiver using a first IF of 48 MHz and a second IF of 5.645 MHz. The same path is used in re- verse on transmit. For the BFO, there is no 5.645 MHz crystal as such, for it is synthesized from 2 crystal oscillators at 8.05 and 13.695. The first mixer is a DBM followed by a grounded gate post amplifier in to a 48 MHz 4 pole crystal filter. On transmit, the 48 MHz transmit signal is routed through the 48 MHz filters, through the post amplifier and into the DBM. The post amplifier has its in- puts and outputs reversed through steering diodes. Output on trans- mit is taken directly from the DBM into the 3 stage high gain PA section (predriver, driver and PA functional blocks). ALC is Drake Mods (09 Nov, 1996) 47
achieved on transmit by use of a diode attenuator in a previous low level stage. The primary reason for the mixing scheme is so full coverage from .5 to 30 MHz can be achieved with a 5 to 5.5 MHz VFO. The synthesizer in the TR7 is a tracking synthesizer. The PTO at 5 to 5.5 MHz is used in the PLL with the divider chain to control a VCO operating at 48 to 78 MHz. If the PTO drifts, then the synthesizer will drift in step with it. o RF Tightness The radio cannot be aligned when extender boards are in use. Some adjustments must be done with the cover plate off. For the other adjustments, there are holes in the coverplate for access. These can only be accurately adjusted with the cover plate in place. Make sure the cover plate is screwed down snugly with all those screws - not just a few. Some boards have grounding fingers. While re-installing these boards, make sure the fingers and tabs make chassis contact. If the above is not adhered to, mediocre alignment and operation will result. There will be RF leakage into the IF section of the receiver. This will have a dramatic effect on S meter, AGC and spurious responses. o AUX 7 Programming See the separate section covering this option in detail. o The FA7 Fan Some manufacturers do not provide for forced air cooling of their PA stages. Ten Tec is a good example. Their PA stages can run so hot that it really hurts to grab the heat sink. I've never seen one 'melt', but having them get that hot gives me the willies. Heat and electronics do not happily co exist (ref TR4 above). While the transistors may take it and good design compensates for it, thermal run away is a concern. Its an ugly event to watch and once started, the event is catastrophic and expensive. The FA7 was an option on the TR7 for heavy duty cycle use. Experi- ence has shown that without a fan, even on SSB, the PA gets inordi- nately warm. Regardless of mode, some form of forced air cooling should be employed. The requirement is to provide air circulation, not necessarily air cooling. The fan should be set up to blow in, not out. This is contrary to the FA7 direction, but seems to afford much better cooling. I mount the fan so it blows in, under the theory fans move more air on the blow side than the draw side. It does seem to be noisier blowing in, though. I really do not think it matters all that much, so long as you can get the temperature down Drake Mods (09 Nov, 1996) 48
and the hot air out. If you mount it to draw, you should feel warm air coming out and the top of the cabinet 'cool'. The FA7 fan runs from 110 VAC and is meant to be run 'through' the PS/7. If you have a PS/7, a 110 VAC 'muffin' fan will bolt right on. If you use a generic power supply use a 12 volt version and power the fan off the TX Vcc from the PA stage. 24 volt DC fans will push a fair bit of air quietly and these are readily available surplus. o Digital Operation All Drakes with the exception of the TR5 use a free running VFO. This may not be stable enough for RTTY as the long term drift is a few hundred cycles. If you must use a Drake for digital operation, your best bet is a TR5 or a TR7 with an RV75 remote VFO (not the RV7). I have no T/R switching times for any of the Drake equipment, but it is reasonable to assume that none of it switches fast enough for AMTOR. * note readers comment on TR7 switching times o Receiver Sensitivity Check The calibrator should provide an S9 signal on 10 meters with no an- tenna attached if the alignment is close. Without an antenna, a properly operating TR7 should appear almost to be dead. If the RF gain is rotated fully CCW, the S meter should rest at the S9 +80 db mark - no higher or lower. Since there is no preselector to peak, the calibrator test assumes the S Meter is set up in accordance with the alignment instructions. The other alternative 'sign of life' tests you can do is to scratch the center pin of the SO/239 with a metallic anything. The S Meter should respond and you should hear the scritch noises most plainly in the speaker. You can also connect almost any antenna to the SO/239 and you should hear an increase in background noise, however slight - even on 10. o Receiver AGC Set Up Notes Aside from alignment, set up in this area has considerable affect on the receivers sensitivity and AGC 'personality'. Also important is the 10 volt regulator adjustment, for it too will have an effect on oscillator alignment, AGC and sensitivity. Tests indicate that at 9 volts, the receiver and AGC setup is quite 'mushy'. For all prac- tical purposes, the 10 volt regulator adjust is the one adjustment that will determine how 'crisp' the radio is. o Transmitter Output Check
Drake Mods (09 Nov, 1996) 49
A TR7 should produce 150 watts output on 80 meters if set up prop- erly. Current draw will be 22 amps at 13.6 volts. Use no smaller power cable than #12 for short runs and #10 for 15 feet or more. You should be able to disconnect the transmitter load and key the transmitter to full output. Properly set up ALC will limit the out- put 'power' to 20 watts or so. If you pull the blue wire from the ALC board (the one between the shielded cable and the red wire on the LHS), the PA stage will run wide open and I've measured over 225 watts output on 80 meters. Not recommended as a normal practice, but this is a good test of final transistor health. Set to its nominal 150 watt output, a TR7 is definitely loafing along. o Won't Transmit The TR7 has a separate pin on the power connector for +13 volts to the PA. Out of the 4 pin power connector pins, 2 are ground and one pin each is for the radio proper and the PA. Ensure that the PA stage does have 13 volts. The transceiver will make all the right noises (relay closure, etc), but won't generate any RF. This is a common oversite. Its comparable to not having plate volt- age for the PA stage in the TR4. o Accessory Filters The TR7 filters are not interchangeable with the R4C filters. The R4C accessory filters are 5695 kHz and the TR7 are 5645 kHz. The factory supplied SSB filter is a 'fidelity' filter. Your transmitted audio with a properly set up radio and a microphone should sound like FM broadcast. The skirt roll off is just a little 'soft'. You need to go to a 1.8 kHz filter to get much RX improvement. The stock SSB filter is quite good in receive. The TR7 always transmits through the SSB crystal filter supplied with the radio. You can put the other 3 filters where ever you want, but don't mess with this filter in this position. o AM Filter An AM filter is almost impossible to find. You can fake an AM 'fil- ter' by putting a 390 ohm resistor through the input and output pins of any blank crystal filter position. It actually isn't bad. What is determining the selectivity is the 48 MHz first IF filter. o Transmit Power Pay particular attention to the SWR balance trimmer, C1901. ALC action is affected adversely by an improper null. This null trimmer also affects the wattmeter calibration, so if you change the trimmer setting, R2001 and R2002 will need adjustment also. Essentially, the FOR output is used for ALC and the REV output is used for shutdown. Drake Mods (09 Nov, 1996) 50
This is independant of the wattmeter setting. When you set up the ALC null, use a high impedance analogue meter, a non metallic align- ment tool and a good 50 ohm load. There are 2 control settings that affect the ALC. The obvious one is the 'ALC' control on the ALC board in the bottom of the transceiver. The other setting control is the gain pot on the predriver. This control sets the gain by setting the feedback on one of the driver stages (old driver board) or the current in the preamp stage (newer driver board). Properly set, you should have just enough ALC on 10 and as expected, a controllable abundance on 80 meters. Improper set up of the ALC usually means no ALC or will make the mic gain setting overly sensitive and the ALC clamp early on the lower bands. There is additional ALC/drive compensation from the bandswitch for the 10 and 15 meter bands. Extra resistors are switched in on these band settings to provide more drive/higher ALC threshold to provide gain compensation. These resistors have only a very minor effect on drive compensation. If you are having upper band drive problems, these resistors should not be the first suspects. For proper transmitter ALC action it is essential for the PA driver and final stages to be in good condition. 150 watts output should be easily attained on 40 and 80 meters. o External Speakers Unlike the '4 line, the TR7 employs an LM380 audio power stage. This IC is load tolerant and 8 ohm speakers may be used without problem. o Microphone High impedance mics may be connected to pin 4. Input Z is about 750K, but this port is much less sensitive than pin 1. High Z mics are expected to be high output (> 100 mv). o PA Driver Stage At least 2 different sets of boards were used in the driver stage next to the power amplifier. Early TR7s used 3 transistors; the late model board used 2 transistors. In this board, the last transistor is an MRF476. The final amplifier board seems to have remained much the same, but the components around the PA input and output trans- formers were different. The board with the MRF476 predriver most likely was changed because it was much cheaper to make. This in itself is not a fault, but the way it was executed presents some problems that will be dealt with in a separate area. On this board the driver is an MPS-H20. I've used the MRF237 as a replacement because the transistor is biased for about 20 ma - about .3 watt. In my mind this is a little heavy for a TO92 transistor. The MRF237 may also be used as replacements for the SRF2331. These transistors are somewhat unique - the case is the emitter and the collector and emitter pins are interposed. If you orient the transistor so the base (center lead is furthest away Drake Mods (09 Nov, 1996) 51
from you) is in the centre and the transistor is held by the leads underneath, the emitter is the left hand lead, NOT on the right where you would expect a TO5 to be. The case in question is a TO39. If it is necessary to change any of the transistors in this area, you must use heat sink compound on the mounting bases. Most folks use far too much of this stuff. The purpose of this compound is to ensure a good thermal contact between the transistor and the heat sink by filling in the (natural) pits in the metal faces. Thats all its used for. Too much is just as bad as none - its a metal filler only. Do not over goop this stuff! o Late Model Driver Boards The problem with the later model board is the bias network on the MRF476. Its bias level is such that the transistor will go into thermal runaway or may latch up by itself. The 270 ohm resistor from base to ground is not enough to prevent this. The 300 ohm resistor and 1N4005 diode is an acceptable method of providing bias, but with the grounded emitter, there is no way to guarantee thermal stability around the transistor. You'll notice this if all of a sudden the transmitter output drops or, on the lower bands, the ALC is gone and more mic gain is required. You let up on the mic for a few minutes and all is well. If you were to feel the heatsink on the MRF476, it will be very, very hot. It may also be possible that the predriver board 'eats' MRF476s. You find its bad - usually leaky and low gain - replace it, and soon the new one dies an inglorious death also. The cure is to lift the emitter off ground with a resistor. Make a tight bundle of 3 - 1.8 ohm 1/8 watt resistors in parallel. Cut the emitter lead of the MRF476 about where the lead changes width. Re- move the stub from the circuit board and put this resistor network between the emitter and where the the stub went into the circuit board. Removing the stub can be interesting for its soldered on both sides of the board. Yes, raising the emitter will decrease the gain. The degenerative feedback also makes the MRF476 easier to drive, so the net result is a wash. This one change for this specific board type is highly re- commended, especially if you're tired of giving it MRF476's to feed upon. o PA Stage Co incident with the different driver boards, Drake changed the PA stage a little bit around the ferrite transformers. These changes look like they were done to improve stability, and the differences are minor. o PA Stage Bias Setting There isn't any. There is no bias adjustment for any of the stages in this amplifier chain. If your final or driver transistors have suffered catastrophic failure, before installing replacements and Drake Mods (09 Nov, 1996) 52
after removal of the transistors measure the base voltage on trans- mit. Nominal reading is about .6 volts. If higher than .7 volts, further inspection of the bias supply is in order. Failure to do so will likely cause the new set to be compromised immediately upon use. o PA Transistors MRF421MP will replace the SRF2337 final transistors. The MP indi- cates Matched Pair, so order one of these or two MRF421 and ask them to be beta matched. At this power and current level, it is wise to have current balance in this stage. MRF475/2SC2092 will replace the SRF2338 driver transistors. The col- lector is the mounting tab, so don't forget the insulating wafer. MRF476/2SC2166 will replace the TO220 predriver. The driver board changed over the years. The collector is the mounting tab, but its board placement is isolated from the circuit board. Do not use tab isolation hardware. The collector choke makes collector contact through the bolt. The cost of all of the above is about $90 from RF Parts. One final transistor alone is over $63 from Drake. The TR7 will shut down 50% at a 4:1 SWR. This provides more than adequate protection. However, the transmitter draws considerable current from a 13 volt supply. The supply should be rated at 30 AMP ICAS minimum. Marginal supplies and DC power cords will not provide enough current under load and likely will drop in and out under full carrier condition jeopardizing the PA. It is important that a stiff high current supply be employed with the TR7. o ALC Time Constant On the ALC board, the ALC decay time constant is over 1 second. This can be decreased to about 1/2 this value without any ill effects and will allow the ALC to track voice input a little better. Change R1618, a 1 meg resistor, to 470K. o VOX - Transmit Generator Board The VOX requires about 50 mv of microphone input to trigger reliably from pin 1 on the mic connector. On the TR7, it takes a very high setting on the VOX Gain control to make the VOX trip. This is in contrast to the mic gain, where not much is needed at all. C304, a .01 uF capacitor coupling the voltage doubler has a reactance of 15K at 1 kHz. Its value is much too low, especially when the applied mic input signal is divided in half by C320, another .01 (transient sup- pression). Change C304 to a .1 uF. The improvement is such that it will take barely adequate VOX gain to 'acceptable'.
Drake Mods (09 Nov, 1996) 53
I recommend this change for those SSB operators that would like to operate VOX on their TR7's but haven't for lack of VOX gain. I have noticed no compromises inherent with this change.
1.13 AUX7 __________ You can make the all band transmit mod by just cutting one trace for the TX band inhibit line. The other, official way of getting additional bands is through the AUX7. This was an option board on the TR7 series that allowed one to operate the TR7 either crystal controlled or allow one to buy program modules for any .5 MHz segment. Special program mod- ules were ordered for transmit. Use of an AUX7 is a nice touch, for by just rotating 2 swtiches, you can get to any band you want without mod- ifying the transceiver. The option modules were all the same - you 'pro- grammed' the modules by cutting off the appropriate pins from a chart. Drake no longer supports the AUX7 optional band modules, but you can make your own from a 14 pin DIP header and a batch of 1N4148 diodes. Each of these modules will consume less than 13 diodes, depending upon the frequency. Yes, its a lot of diodes. Typically, you'll need 7 or 8 diodes per module. You must use the diodes, for the band modules are ma- trixed. The AUX7 is not easy to install or gain access to for it involves open- ing the TR7. The front panel will flip down, but to do this, you need to extract the bandswitch shaft. If you are not careful, you can rip the wafer rotors out when you extract or reinsert the shaft. This will cause REAL trouble and given the age of the unit and replacement parts avail- ability (don't count on it!), The AUX7 band module has a separate pin for TX enable. Obviously, this pin must be enabled for any of the WARC amateur bands you need or want to enable. The bandswitch must be set to the appropriate filter range. If it is set to a range that does not match the module programming, the SETBAND light will come on. When you set up the DIP header with the 1N4148 diodes, use the following programming chart. The pin numbers are as if it were an IC. Make sure you do not wire it backwards! This is a very common mistake: PIN USE PIN USE === ========== === ========== 1 Select 5V 8 Range B2 2 Range A0 9 Range B3 3 Range A1 10 TX enable 4 Range A2 11 Band A 5 Range A3 12 Band B 6 Range B0 13 Band C 7 Range B1 14 Band D
Drake Mods (09 Nov, 1996) 54
Essentially the AUX7 programming is divided into 2 halves - BAND and RANGE. BAND sets the band as if it were coming from the bandswitch. RANGE sets the .5 MHz offset as if you were to hit the UP/DOWN buttons on the front panel. The BAND programming is compared against the BCD bandswitch wafer. If there is no match against these two, the SETBAND light comes on. This is used to tell the operator that the bandswitch setting does not correspond to the programming and the bandswitch should be rotated until the light extinguishes.
1.13.1 Band Programming ________________________ Band programming is done in BCD to indicate the bandswitch setting through the SETBAND indicator. If this is not programmed, the unit will not transmit. If pin 10 is not made high, the unit will not transmit. Band Range BA BB BC BD ========== == == == == 1.5 - 2.0 - x - - 2 - 3 x x - - 3 - 4.5 - - x - 4.5 - 7 x - x - 7 - 10 - x x - 10 - 15 x x x - 15 - 22 - - - x 22 - 30 x - - x The band range pins BA to BD correspond to the previous 14 pin chart. This programming sets the bandswitch data/SETBAND light. If this is not programmed, the unit will receive, but it will not transmit, even if pin 10 is high.
1.13.2 Synthesizer Programming _______________________________ The synthesizer requires programming in order to set the correct 1/2 MHz range. This requires some calculation. The pins A0 to B3 comprise a 1 byte field to indicate the correct .5 MHz chunk. You simply cannot as- sume that 18 MHz is the 36th 1/2 MHz chunk and program '0011,0110', for there is a modulus to be accounted for. The formula is 86 - (F*2), where f is in MHz at 500 kHz settings. To set the synthesizer to 27.0 MHz, you would calculate 86-(27*2) = 32 = 0011,0010.
Drake Mods (09 Nov, 1996) 55
0 0 1 1, 0 0 1 0 PIN | | | | === | | | |___ A0 2 | | |_________ A3 5 | |____________ B0 6 |__________________ B3 9 To program this 27.0 matrix, you would connect diodes from pin 1 to pins 3,6,7 for the synthesizer, diodes to pins 11 and 14 for the bandswitch, and a diode to pin 10 to enable transmit. (but we'd NEVER do that, would we?). The TR7 has 2 master oscillators that are selected by the bandswitch, NOT the frequency programming. Although it is not obligitory for recep- tion, you should also program the bandswitch data so the SETBAND light will come on. A common error is to do the diode programming, fire it up and the synthesizer won't lock. This is usually caused by the bandswitch in the wrong position. The band programming and the SETBAND light is de- signed to prevent this.
1.13.3 Crystal Control _______________________ Crystal control on the TR7 is independant of the programming matrix., The PTO tunes up and is offset 50 kHz, so finding the right crystal is f + 5.05 - f(MHz). To crystal control to 7.055 MHz, you'd order a crystal for 7.055 + 5.05 - 7 or 5.105 MHz. For bands that are on a .5 MHz bound- ary, you'd subtract an extra .5 to put the crystal within the 5 to 5.5 MHz range. The above crystal would put you on 3.555 MHz on 80 meters (3.5 + 5.105 - 5.05). Since crystal control is related to a specific band, you should program the AUX7 as documented above. This is not mandatory. I do not have specs on the crystal, but an educated guess would be HC/25U, 20 pf, series, fundamental.
1.14 R7 RECEIVERS __________________ The receiver is very similar functionally to an Icom R71A or Kenwood R5000. The R71A is an excellent communications receiver. This is excep- tional company to be associated with. This is a triple conversion receiver, somewhat like an R4C. The last IF frequency is at 50 kHz in order to encorporate a notch filter. The sig- nal flow is crudely similar to an R4C, but the unit is more akin to the receiver section from a TR7 with the following exceptions: o Notch Filter Drake Mods (09 Nov, 1996) 56
In order to use the syncronous AM detector properly, the optional 4 kHz filter needs to be present. **************************** END ***********************************
Drake Mods (09 Nov, 1996) 57
2.0 DRAKE PRICES _________________ The following represent a sampling of the prices of various Drake equip- ment at the time they were sold. These are actual dealer prices and therefore there will be some variation. Unit Description Price hi/lo ==== =========== =========== TR4 Transceiver 599 TR4Cw Transceiver 799/699 34PNB Noise Blanker 100 FF1 Crystal Control 47 MMK3 Mobile Mount TR Series 7 RV4 Remote VFO 150 TR5 Transceiver (1983) 695 TR7 Transceiver 1100 TR7/DR7 Transceiver 1295/1195 TR7A Transceiver (1983) 1445 DR7 TR7 Digital Display 195 PS7 TR7 AC Power Supply 195 MMK7 Mobile Mount kit 50 FA7 Fan 25 RV7 Remote VFO 195 MS7 Speaker 33 NB7 TR7 Blanker 90 MN7 250 watt coupler 165 WH7 160-6 M wattmeter 89 AUX7 Range pgm board 45 RRM7/RTM7 Range RX/TX module 8 385-0004 Service Manual (NLA) 30 SLxxxx TR7 Crystal Filters 52 MN2700 1000 Watt Coupler 279 DSR-2 Receiver 3200/2950 SSR-1 Receiver 350 2-C Receiver 229 SW4 SW Receiver (1966) 299 SPR-4 Receiver 699 R4A Receiver 399 R4B Receiver 475 R4C Receiver 699/599 MS4 Speaker 33/30 FLxxxx R4C Crystal Filters 52 NB4 Noise Blanker 70 FS4 R4C Synthesizer 300/250 R7A Receiver (1983) 1395
Drake Prices 58
Drake Prices (cont'd)
Unit Description Price hi/lo ==== =========== =========== 2NT Transmitter - CW 129 T4X Transmitter 399 T4B Transmitter 495 T4C Transmitter 699/599 AC4 Power Supply 150/120 DC4 DC Power Supply 195/165 DC3 DC Power Supply 149 MN4 300 Watt Coupler 120 MN2000 2000 Watt Coupler 250 B1000 4:1 BALUN 25 W4 Wattmeter 79 L4B Linear Amplifier 995 L7 Linear Amplifier 995 7072 Hand Held Mic 19 7073 Hand Held Mic 19 7075 Desk Mic 39 7077 Desk Mic 45 DL300 300 watt dry dummy load 20 DL1000 1000 " " 40 UV3 VHF transceiver 595 UV3 220 or 440 module 175 PS3 UV3 power supply 90 UMK3 UV3 Remote trunk kit 70 1525EM Hand Held Mic w/TT 49 WV4 VHF Wattmeter 89 Price hi/lo represents the extremes of price range I've seen within the same time frame between dealers. This is in US $.
Drake Prices 59
3.0 AUTHOR'S NOTES ___________________ Anyone who contacts me for assistance will get it. I cannot say I'll make the badness go away, but I will give it a good shot. Past experi- ence has shown that trouble shooting at a distance is frustrating at best, but if you're stuck, I'm available. If you've found an error in this document or if its caused you grief, then I WANT to hear from you. Please. Where comparisons were made to other equipment or statements of 'func- tionally like' were indicated, they were done for illustrative purposes only. I have heard manys a time Drake to be referred to as a "poor man's Collins." While I understand what is implied here, it is in a way an in- sult. Collins never really did make equipment for the Amateur. What ama- teurs got from Collins was commercial/military gear. Its analogous to saying a Kenwood TS450 is a poor man's SG2000. Its almost a meaningless statement. Drake, with the 4 line, made the best amateur market equip- ment available at that time in the whole world. So good, as a matter of fact, a large percentage of this equipment is in service today and will hold its own in a dignified manner. There is not one piece of Drake equipment that I know of (R4C excepted) that was not the best it could be. Supposedly we make things 'better' now. But what is 'better' if the equipment is designed for a specific lifespan and made no stronger than it need be for its intended application? 'Old tech' equipment employed construction techniques that are tried and true instead of new, trendy and 'the Next Generation'. The American equipment of the era of the 70's had a completely different engineering philosophy. I've stated before that Drake equipment is well built. Additionally, just about every product in their HF line would work together in some form despite the changes and progress made over the years. You could connect an RV4C to a TR3 with but only a very minor change. I can connect my R4B to my TR7 and get antenna switching and mute. This is from the same manufacturer using two entirely different levels of technology manufactured over 10 years apart. This is in con- trast to todays commodities that are replaced constantly with a whole line of new accessories. Rather than improve upon a radio, todays gear is replaced by the manufacturer en mass. While the parts availability from Drake won't last forever, you can still get them for a 25 year old radio. An S meter for an R4B is less than $15. And Drake hasn't made amateur equipment in over 12 years. I'll allow them their front panel policy as silly as it sounds, for their support is absolutely top notch and every bit as good as the other highly respected manufacturer of ama- teur products. Drake is America's best kept other secret. Author's Notes 60
I too lament Drakes departure from amateur radio. I suspect they, like others, got out of it for the reasons that have come true today. Selling ham gear is a cut throat business left to the big 'dealers'. There is no longer brand allegance, but price allegance given to the lowest bidder with a 1-800 number. A $20 difference in price will kill the sale on a $2000 transceiver. To stay in the game you have to be a player with an army of engineers and a 'new' product line every year. Drake and others saw this coming and went for a more stable market for their electronics. I hear stories of people asking Drake to 'come back'. Look at what the amateur market has become today and ask why any domestic manufacturer would bother. Based upon my experiences with the TR7, I'd purchase a modern Drake HF transceiver instantly. 'All' Drake need do is update the TR7 to the 90's. I have an SW8 and it has 'Drake' written all over it. Not the most extreme in technology and with some operational idiosyncracies, but the audio and AGC scream Drake and 'modern SPR4' loud and clear. Drake has not lost their touch. While I will not use this as an opportunity to disparage foreign equip- ment, personally, I've had my fill of this stuff. While it arguably is well made and engineered, 'marketing' has overshadowed the commu- nications equipment it could be. It gets better slower than it gets re- placed with a new product line with yet more buttons, knobs, LEDs and chrome. What started my Drake exploits was pure happenstance. As is not unusual these days, I used to own a considerable count of Japanese equipment, but in the last few years I realized something was obviously missing. Call it 'soul' if you will. Maybe it was triggered by a visit to a stereo store, or maybe it was that woebegone orphan of an SPR-4 that I saw at a flea market. "He followed me home, can I keep him?" Having danced with Japan for a number of years, I realized that they stopped making communications equipment. What Japan makes these days is 'commu- nications entertainment devices'. I went out looking for some honest equipment and discovered how good Mr. Drake's wares were. I also discov- ered and confirmed that what you really need for some enjoyment of this hobby isn't all that much. The arms dealers will try their best to sell you a $6000 Death Star, but unless you're trying to run communications intercepts for the NSA, you don't need this stuff. My apologies to Mr. D. Vader. But I may be preaching to the converted. I do not profess this to be 'the' definitive Drake bible, but it is at least not a bad start. I would like to think, and I do hope, that some- one that wrote off a Drake with a bad PTO has been able to dust it off and fix it with a bit of glue. Unfortunately far too much old gear gets written off because fewer people have any idea just how well it really works. It ends up rotting in someones garage for lack of just a little TLC. I wrote this article for a few reasons. First, I wanted to publish what- ever maintenance tricks I had learned. I wouldn't want someone else to Author's Notes 61
learn the hard way as I did. Life's too short. Second, I believe that it is important that mods and data regarding this equipment should be available. The intent of this paper is not only to put on paper some mods - I wanted to have some kind of a record indicating what this gear was like. Not only is this equipment part of our heritage, Drake and others made some excellent products. An increasing percentage of ama- teurs every year have no idea what Drake, Collins, Hallicrafters or even Heath were all about. I see far too many hams swallowing QST dogma about the latest and greatest from KenYaeCom. Its a hobby guys. _____ More than anything else, I guess, was the initial frustration I had get- ting information. Drake equipment and its expert enthusiasts were hard to find and were somewhat akin to visiting the Great Owl. I decided that anyone that wanted to follow my path shouldn't have to go through this. One may read into this that I am a 'Drake expert'. This, I do not pro- fess to be. All I've done is kept my eyes and ears open, had some experiences, and wrote them down for those that are interested. There is a wealth of information out there and I almost think that its kept quiet in order to maintain mystique and exclusivity. This is something that old farts do, unconsciously, for some reason or another. Where Drake is concerned, not any more. "I blew it up. I had to" Wayne Montague, VE3EFJ 4146 Marigold Crescent Mississauga, Ont Canada. L5L 1Y7 C/Serv (73057,3063) I/net email@example.com
Author's Notes 62
4.0 READER FEEDBACK ____________________ Included here is some of the feedback I've received. I've included what I think is most interesting and what provides some additional infor- mation. Where no originator indicated, it is because I've edited it out. The "...." indicates further editing that I felt was not pertinent to the subject at hand. Those that wrote and wish to be credited will have corrections in the next release of DRAKEMOD.
4.1 THE TR7 ____________ (someone with MUCH more experience than I have) Wayne, I have read with interest the three versions of your drakemod.txt file and appreciate the time and effort you have obviously put into it. I have no knowledge or experience of the Drake 4-line, and that makes up much of your document. However I can offer some comments and amplifi- cation on the portion of your work that deals with the 7-line and its commercial derivatives (more about that later). First, let me introduce myself and detail my association with Drake equipment. I am very active in HF digital work and have run an APLink/WinLink MBO system for many years. My first piece of Drake gear was a TR7A that I bought new in the mid-80s. I feel the same way as you do about the quality of construction and performance of this gear. The R7 and derivatives have just about the best receiver I have ever seen, and that is saying a bit. My daytime job is with a commercial maritime service provider (HF) and we have evaluated many expensive receivers with names like Harris, WJ and Racal. I always bring them home and com- pare them with my Drake R4245 (an R7 inside, see below). The Drake stands up to all of them. Yes, they are fancier, computer controllable, DSP based and all of that, but in basic receive performance the best that they can do is equal the Drake. My radio shack consists of several 'systems', separated by functionality. In the descriptions below I have ommited the details of the digital hardware software and concetrated on the radios. Twenty Meter MBO system - a TR7A (w/PS7) slaved to an R7A, both driven by the same RV75. I have modified the RV75 to scan eight channels on the 14 MHz. band. The transmit antenna is a Butternut vertical on the carport, and a dipole serves as a separate receive antenna .... Thirty Meter MBO system - a TR7 (w/PS7) driven by another RV75 with similar mod, scans .... Reader Feedback 63
HF Intercept system - a Drake R4245, an Icom R71A and various digital modems and decoders. This system .... In addition I also have a complete marine test 'ship' setup with with Raytheon and Furuno radios where I do software and hardware testing for the day job. Drake also sold a commercial version of the 7-line. The transceiver was called a TR4310 and the receiver a R4245. I have little knowledge of the TR4310 except a description in a four page brochure. (I would be happly to fax you a copy.) However, I do own an R4245 and can describe it briefly for you. It is in a rack mount cabinet. Upon removing the top and bottom covers, one finds an R7 mother board and card cage. The major change is that the PTO is gone, as is the DR7. In place of the DR7 is a board that contains circuitry similar in function to the outboard RV75. This makes it fully synthesized, very stable radio! Other changes in- clude different style knobs (but everything is in the same place as on an R7) and a light beige paint job on the front panel. The default fre- quency ranges when you switch bands are not the ham bands, but the mari- time bands. The radio will run from 12VDC, 24VDC or 110VAC. I obtained the unit, new, during last months of operation of the old Harvey Radio store on 45th Street in Manhattan. I passed up a TR4310 at the same time and have been kicking myself ever since! Your comments on the TR7's capability for digital operation need a bit of detail added. First, you are correct that the internal PTO is not adequate (stability-wise), that is why I use the RV75s. However, these radios turn around very quickly and are ideal for AmTOR use. I TR7 is a bit slower for some reason, but still under 10 ms. Yes, there is a bit of noise from the clacking relay. In fact, I had several years ago purchased two replacement relays, anticipating failure, but both transceivers are using their origanal re- lays, believe it or not. Several articles have been published with improvements for the 7 line over the years. My library is not organised at the moment, so I will mention what I can from memory. Given some time, I can dig out either a reference or a copy for you, if you are interested. There was an article from an author in Switzerland detailing a stabili- zation mod for the PTO in the TR7. It consisted of a board, mounted un- der the mother board, that sensed a change in the least significant digit of the counter on the DR7 board and 'bumped' the PTO back on fre- quency if it drifted far enough for that digit to change. It 'bumped' in 10 Hertz steps, as I recall, which I thought might be too much for dig- ital work, so I never tried it. Also, I had acquired the RV75s by that time. There have been many mods published over the years to allow full fre- quency transmit with the TR7. Most simply leave the transmit enable line high at all times by cutting a trace. Because internal signals like PLL unlock can drive this line low, I developed a mod that left this impor- Reader Feedback 64
tant protection in place. I have not looked at the mod you got from Drake to see if it also does this, but I will. One author claimed that he had seen low level spurs on both transmit and receive caused by the 23 kHz. oscillator in the +24 volt supply getting back into the +10 volt line. He suggested adding additional filtering to supress it. I have never seen this problem, but do have the parts on hand if I want to make this mod in the future. Similar circuits are used for this supply in the TR7, R7 and R4245. Another article included several unrelated TR7 mods. The ones I recall were a temperature sensing fan driver and replacement of the TR relay with PIN diode switches. Circuit boards were available. Your comments on fans are interesting. I have an FA7, or homemade equiv- alent, installed on both TR7s and on both PS7s, but using the Drake ap- proach, blowing out in all cases. Also, on the subject of heat and fans, I run both the R7 and the R4245 from external 12VDC, which reduces the internal heat somewhat. In spite of that, the regulator on the rear panel runs quite warm, so I have arranged a fan to move air in that area also. I could go on and on, about such things as changes to the Drake transceive cable kit, a mod to remotely switch between 10 MHz. and 14 MHz. operation. however, I suspect that this is enough for you to chew on for the moment. 73, Craig (writer detail omitted)
4.2 A 2B OWNER _______________ Date: 08-Jan-96 09:05 EST From: Max Lockwood > Awesome Drake article Hello Wayne, Thru Dave (deleted) and with your permission, a copy of your treatise on Drake radios has been made availble to members of the "boatanchors" mailing list. I've read it. Great stuff!!! I noticed a relative lack of information on the 2B in particular and the 2 series in general. Are you interested in adding anything about these radios? I don't have much info, but what I do have could be useful to someone someday. For example: One of the weak areas in the 2B seems to be in the crystal oscillator circuit. It's apparently common for the crystals to cease working. If you have multiple 2Bs (as I do), you can frequently play "musical crys- tals" and come up with combinations of rocks and radios that still work. Failing that, JAN crystals still has design data for the 2B and will custom grind crystals for about $13. Reader Feedback 65
Another weak area is the Sensitivity control on the back of the 2B. A 2 meg pot used to adjust the AGC bias, it's not uncommon for it to develop a high resistance short to ground. Such a short can be the same order of magnitude as the value of the pot itself, 2 meg. It completely upsets the AGC circuit and results in an inability to mute the receiver com- pletely. If it is necessary to paint the cabinet of a 2B, an extremely good color and texture match can be had by using Rustoleum Satin Black, available in spray cans or in bulk. If this kind of information would be welcome in your article, feel free to incorporate. All I ask in return is credit for the information be in- cluded with the article. One other comment: I was really glad to see your remarks about the R4B. I have two of theses and am just blown away by their performance and their sound. (further comments deleted) 73 and thanks, Jim Lockwood - km6nk ps. 'boatanchors' is a special interest group of 'vintage' radios. There is heavy interest currently in the R/390 series. Boatanchors is located at 'firstname.lastname@example.org'. You subscribe by sending E/mail to that address - 'SUBSCRIBE BOATANCHORS (your name)'. A TR7, R7 or a TR5 is NOT a boatanchor, by the way. If you don't know what an ART-13, Sky Buddy or an SX-101 is, this site may not be for you.
4.3 JUST SAYING 'HI' _____________________ Date: 08-Feb-96 18:18 EST From: Tim (deleted) Wayne, just read your article Drakemd3.zip. I am just coming back to Ham Radio after an absence of 30 years...gave it up when I went to college. I was talking to my old Ham chum and classmate of the 50's and he men- tioned that he had an old Drake from the 70's that he would let me use when I get my license. Think he said it was a Drake 3B but i'll find out for sure tomorrow. Anyway, I was fascinated with your piece on the Drake's and I thought I would drop you a note of appreciation for you fine effort on everyone's behalf. I too have felt something lacking in the current breed of xcvr's when you actually try to sit in front of one for a few hours. My brother-in-law is a first time, enthusiastic, about- to-be Novice ham who plunked down about 1200-1500 bucks for an assort- ment of Kenwood stuff including a TS450/AT. Scanning the bands with it left me wondering what was missing. Maybe it is the wide open spaces of 1958 sunspot peak etc but I suspect your opinion hits closer to the mark. Thanks for a great read. Reader Feedback 66
regards, Tim (deleted)
4.4 EXPERIENCES .... _____________________ Date: 10-Feb-96 17:40 EST From: Garey (deleted) Subj: Drakemd3 File Wayne: I really enjoyed reading your Drake "Masterpiece" file. I became a convert in about 1961 when after being out of Ham Radio for a brief period I fell victim to a QST ad from (an amateur dealer) in Milwaukee for a Hammarlund HQ-170 at a "closeout" price. After about a week I got a letter from them saying that they were all out of 170's, but would be happly to sell me a "new 170A" for only a few more dollars!! My only excuse was that my last commercial receiver was an HQ-129X that served me well. Anyway, I fell for it. When it arrived, I set it up on the kitchen table in my apartment. The first night it never stopped drifting. I noticed that Hammarlund had ar- ranged the vfo tube filament to be on "all the time," and so I left it plugged in and went off to work the next morning. When I came home from work, it was still drifting!! The thing is probably up past S-Band by now!! Anyway, I took it to my friendly local ham emporium and traded it for a 2-B. Smartest move I ever made. Since that time, I have owned the R-4, A, B, and C lines in approximate chronological order. I never owned a T-4 however. I have never owned a "bad" piece of Drake equipment. My first T-4X, which I drove Drake crazy for after it was first announced, had a serial number of 10102. I found three unsoldered connections in the carrier oscillator area, but once they were soldered, the tx worked for many years with no problem. When I talked to Drake's service department they said I couldn't have that serial number because they never shipped anything below 10200. So maybe they just got tired of me bugging them and sent me a prototype or pre- production model!! I used these rigs for RTTY autostart for years, 24 hour duty cycle with sometimes 30 minute key-down times. I always used a small "Sprite" fan bolted to the back of the TX cage and would get 3-4 years out of a set of 6JB6's. Sylvania only, of course. Anyway, now that I have worn out your eyes, I will say that of all the equipment I have owned, I always go back to the Drake. I currently have two C Lines with all Drake filters and NB installed. The only mods I have done were the Sherwood audio amp replacement with the LM-383. They were quite specific about the layout and bypassing of the chip, and I never had a problem with either one. I built the amp on a small (1.5" X 1.5") piece of copper flashing, and RTV'ed it to the shield divider be- hind the AF Gain control. Finally, (whew!,) I spent some time working part-time for a Ham equip- ment retailer in the 60's and spent many "working" hours comparing the Reader Feedback 67
S-Line and the C-Line trying to decide whether to abandon the Drakes for the Collins mystique. At that time the Manufacturers of ham gear would sell their wares to sales people for 50% of list price rather than the "normal" wholesale of 75% and that brought the Collins down into the "possible" range for the working man! I couldn't convince myself that the Collins was worth the price, and stayed with the Drake. Today the C-Line is on the operating desk and the S-Line is on the storage shelves with the "back-up" C-Line. I know that many (most) of us fail to recognize the work of people like you who take the time to chronicle this sort of information for the "in- grates" of today and tomorrow!! I am as guilty as most, and after wad- ing through all this, (if you get this far!,) you will wish I had kept quiet!! Again, thanks and 73. Garey