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
Drake Mods (09 Nov, 1996) 5
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 montaw@inforamp.net
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 'boatanchors@theporch.com'. 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