Tram D201 no modulation

[scj483]

Hi guy's.
Hopefully someone can point me in the right direction here, I just acquired a Tram D201 from a guy who sent it off to be gone through and had a DDS VFO, HF RX board and something else added to it, it had been sitting on his shelf for a couple of years he said because he couldn't get the VFO to work or something like that, so now I have it, minus the VFO and anything internal pretaining to it.
I wired my 1978 bone stock amplified D104 for it, and turned it on, at first it wouldn't key, found that the TR jack wasn't making contact so fixed that, then moved on, it receives great on AM and SSB, in both crystal and manual, but when I key the radio it is transmitting a 4w carrier on AM and 10w on SSB, and no modulation at all, none, zip, zero, so that's where I'm at with this thing, don't understand why it is transmitting a carrier on SSB mode in either crystal or manual mode, and from what I can see the TX mod to the manual tune hasn't been done so go figure, any help here would be awesome!.
Thanks
Tim.

[2600]

If you had an inline frequency counter on the radio's coax, I suspect it would be reading a frequency that's NOT near the selected channel when you transmit sideband. This is caused when the transmitter's amplifier stages oscillate. In AM mode, the carrier drive from the driver tube tends to suppress this feedback, and that inline counter would probably read the proper channel frequency. We'll skip the sideband problem for now. This is usually caused by someone tweaking an adjustment that cancels out unwanted feedback. That is, until someone twists that adjustment randomly hoping to make the wattmeter reading higher.

That radio was made in two basic internal setups. First version had the tube sockets mounted in holes punched in the metal chassis deck. Common nickname for this one is "hand wired". If yours says "Made in Mexico" the small tube sockets are mounted to large printed-circuit boards. Never mind that the later version with the printed circuit boards was also wired by hand at the factory, that's what the CB operators call the original radio built with what the industry calls "open chassis" or "point-to-point" assembly with the small parts all strung in midair between tube-socket lugs and tie strip lugs. Any specific advice about where any part is located will be correct only for one or the other version, but not both.

The mike audio is first amplified by the pentode half of V601. First thing to suspect when a tube radio breaks is a failed tube. But I'll stick my neck out and suggest that a capacitor shorted to ground on pin 3 of V601 is your culprit. A voltmeter probe to pin 3 should read between 25 and 30 Volts. If it reads zero, C610 is probably shorted. It's a 4uf 160 Volt electrolytic. A cap rated at 100 Volts or more will work fine. The resistor that feeds into pin 3 is also a chronic fail. It's R620, 470k 1/2 Watt. We use a 1 Watt or 2 Watt to replace it just as cheap insurance.

This symptom is a little like "my car won't start". More than one possible cause. Bad mike-gain control, failed tube, other failed capacitor, etc.

If nobody has mentioned the age issues of this radio, consider that it is full of electrolytic capacitors large, small and in-between. A radio that anyone wants to depend on will need to have every, single one of them replaced. Age alone causes them to fail even if the mileage is low. And mileage wears them down as well. There is a whole laundry list of other routine details to performing a 45-year tuneup. For now, put a meter on pin 3 of V601 and see if I'm right. If not, you didn't waste a lot of effort to find out.

73

[scj483]

From what I can tell it looks like all caps have been replaced, and some resistor's, please forgive me on some of this stuff I'm old and starting late on testing protocol, I understand HV and what it can do, I know a bit about this stuff just not as proficient as most of you, I believe mine is the second gen D201, there's a stamp on one of the CB that indicates maybe 1976 era?, Anyway I have located V601 however I'm unsure about which is pin 3, thank you for your response and offering to help.

[2600]

Um, okay.

There is a gap in the pin circle of the small tubes. V601 has nine pins, and number one is the first pin clockwise from the gap, around the circle to pin 9 at the opposite side of the gap.

The common practice is to show the pin arrangement for tubes as seen from under the socket.

73

[scj483]

Okay checked pin 3 of V601 it's showing 25.8v

[scj483]

Update!!!!!....

Radio is fixed, there was actually two issues, 1- the no mod was two wires broken in the mic, my fault I just didn't see them, so problem 1 is solved.
Problem 2, the carrier on SSB it was just an adjustment, when the load and tune circuit was retuned everything started working, so problem 2 solved!.

The tone of this thing on AM is absolutely stunning, I wish there was a way to get the SSB tone to be as good as the AM side.

So having said that my next problem is the manual tune side, I did the TX mod to the manual tune, it works however as long as it's just RX it's stable, as soon as I start TXing it just takes off, is there anyway to make it stable?, I was told to get the DDS VFO and add that to it, the reason for wanting this stable is because I live in 37LSB so like to have it working up there and stable.
Thanks.

[2600]

A DDS VFO will take care of the problem. What makes the VFO drift when you key the mike is the tiny drop in heater voltage caused by the higher power drain of transmit mode. It's a tiny drop, but the VFO frequency is exquisitely sensitive to heater voltage changes. Never have tried to regulate the heater voltage to V302. Would probably fix the issue.

73

[scj483]

Thanks may try that, someone said use a zener diode and a resistor to help with voltage drop on VFO but they couldn't remember what resistor value to add to it, might get the DDS VFO, kit rather have it in the radio than have an external box.
Thanks again.

[2600]

A zener diode is a waste of time. The plate voltage on the VFO circuit is around 100 Volts, but regulating it won't fix the underlying cause. It's the filament voltage on the tube that makes it drift when the mike is keyed. Regulating the plate voltage won't affect that.

73

[scj483]

Good to know Thanks, contacted Troy radio service about VFO kit, Thanks again.

[2600]

Good deal. Troy's the real McCoy.

73

[scj483]

Thanks again!.
Haven't got a chance yet to do anything with the DDS VFO yet, race car season lol.
I managed to get the studio audio rack gear on it and have been playing with it, seems doing and I like the sound that's it's producing of course AM is so far different than SSB quality in this rig not sure if that's fixable as 99.9% of what I do is SSB work anyway, I do have another question, I tried to plug my stereo receiver stuff I use on my Yaesu to the Tram and it's really really low output coming out of the ext spk port, I tried different speakers, straight out and into the receiver, still same results, anything other than the front speaker it's low and crappy.
Any idea how to improve this?.
Thanks again!.

[2600]

Umm, so is the receive audio poor on both AM and SSB?

Which version of the radio is this?

Makes a difference.

73