- Low Transmitted Output
Many things can cause this, of course. With a low capacity 'scope
probe, you should have about 45 to 50 V P/P on the 6JB6 control
grids for full output on either the T4any or TR4any.
Have a look at the following. This might help:
- - Not all the finals are connected.
Sometimes when you replace a final tube, you'll fatigue the
parasitic suppressor solder joint at the plate choke. This will,
of course disconnect a tube. It is also very bad, as the discon-
nected tubes' screen will draw much, much more current than it
was designed to. All that cathode current has to go someplace
....
- - The units meter is lying
All the B and C line meters seem to be about 5 ma. in movement.
Age may make them go non linear, not rest at zero or cause them
to lose their damping.
- - The watt meter is lying
Does the measured output correspond to the indicated current?
- - The cathode meter resistor is cooked
Usually they cook high in value (ref prev item).
- - The power supply is soft
The filter caps are immediately suspect or the supply is set to
220 VAC.
- - Alignment
Pick ONE band - 80 meters and adjust. If you can substantially
improve the output, then chances are the rest of the set needs
some set up attention.
- - BFO off frequency
If the BFO falls on the Filter slope on CW or tune, the output
will be low. In either sideband position, a counter will tell
you if its off. Set the crystal trimmer to 5645 kHz in either
sideband position. The crystal is pulled in the tune and CW
positions.
- Band Sideband Filter
This will also apply to the TR3 and TR4 series transmitters.
There are no replacement filters available. In the TR3 and early
TR4 the sideband filter is composed of discrete crystals inside
the square can. You might be able to get a replacement crystal
cut, but finding the offending crystal in the first place will
prove to be a bit challenging.
- 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
(175 ma, T4; 250 ma, TR4).
- Transmitter Keying
For all receivers and transmitters in the 4 series the keyed voltage
level is negative. The TR7 has a positive switch line.
- 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. Information relayed
to me from the Drake User group indicates that even Drake themselves
does not bother with the loading network any more.
- Transmitter Neutralization
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 watt meter. 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 oscillate. 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 in operation. DO NOT touch the blade
of the screwdriver while adjusting.
- 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, operated 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.
- 'A' Tubes
Some have asked about the 'A' designation on vaccuum tubes. Specifically, whats the difference between a 6JB6 and a 6JB6A? What makes an 'A' tube different from a 'blank' tube?
In almost all cases, we are dealing with vaccuum tubes that had a
television application. The 'A' usually indicates "controlled heater
warm-up". Tubes do not come active until the filament heats the
cathode to dull incandescence. There is a time specification -
usually 11 seconds. The 'A' usually means this figure is
guarantee'd.
Note that this designation does not necessarily apply to transmitting tubes such as the 6146, the 829 and others.
- 6JB6
These are sweep tubes used in the horizontal driver in television
sets. They are rated for 17 watts plate dissipation. These are high
pervience tubes (high cathode current with relatively low plate
voltage). The tubes are not designed for RF work. Drake made a
reasonable tube selection and at the time, picked an inexpensive,
very common tube. The basing diagram is such that there are few direct substitutes. The FT101 uses 6JS6 (not pin for pin to 6JB6).
Some folks have modified the transmitters to use the 6146, but this
requires considerable work, for the tube sockets require changing
and the holes enlarged. Then there is the matter of recessing the
sockets. To run 6146s, you also need a plate voltage around 800
volts. What all this serves, I have no idea.
Final amplifier tubes are becoming expensive. It is this fact that
will be the one item that will kill off tube equipment as the years
go by. Vaccuum tubes will be available well into the 21st century,
but the price has no place to go but 'up'. When you replace the
finals in your Drake, you can slow down the inevitable for quite a
while by installing a fan. If the equipment is a genuine keeper, you
should purchase a new set tubes, plus a spare set at the same time.
The following is a reasonable list of sources for the 6JB6 and other
tubes used in Drake equipment:
- - RF Parts (see QST ads)
- - Antique Electronic Supply (1-602-820-5411)
- - International Vaccuum Tube ('generic', see QST ads)
- - Radio Shack (oh, you'll pay for this)
- - Radio Shack "Life Time" (yessss!)
- - Try Fair Radio (its worth a shot)
- - Swap Nets
- - Boat_Anchors
- - Flea Markets
- - Drake User Group
At one time Radio Shack was selling 'Life Time' tubes. And yes, they
were selling 6JB6. If you see a set at a flea market, buy them. Do
not hesitate. Even if they are bad, any Radio Shack dealer will get
you a brand new set, but they really try to avoid this, for obvious
reasons. You will not get 'life time', but you will get a brand new
tube without paying a cent more.
The kid behind the counter ('You got questions, we got blank
stares'), likely will not have a clue what you are talking about,
but stand your ground and go for it. Do not leave the store without
having your new replacement tubes on order. Radio Shack will honor
their 'life time' replacement policy. Its now one shot. Its not your
life time - its *that* tubes life time.
This applies to any Radio Shack tube marked "Life Time". Its a great
deal. Buy the tube at the flea market and use it. If its shot, or
when it goes, take it to Radio Shack and get a new tube for free.
My only regret is that Radio Shack never sold 8877's ....
- 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
some minor inconveniences will be suffered such as loss of active
PTO indication and the requirement of BFO netting prior to operation.
But it will work.
- 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 that the BFO fre-
quency 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.
- 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 output. The push required is considerable and is a result of the spring strip tension and the spring in the return switch. Never try to
adjust 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 itself are completely seated to the LOAD variable capacitor.
- 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 going 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.
- 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.
