Tram D201A low SSB RF output above channel 16

[ScannerHam62]

Hi guys,

I'm new here on this forum and appreciate the comments.

Anyway, here it goes. I have a Tram D201A that works great on AM, (at least 5 watts output and good receive), but on SSB the power drops from 12 watts (or more) to around 1 to 3 watts above channel 16. The radio has the VFO modification to open to transmit and that's what I am using but it does the same thing in crystal mode. After scouring the manual, I think its either the Balance Modulator Board or the ALC circuits on the RF Bridge board. I have removed and reseated the Balanced Modulator Board but that didn't help. I guess I'm not sure which one I should concentrate on or look at something else. The unit actually seems to do better with the mic gain lower rather than higher. Not sure why it drops off above channel 16. Occasionally the SSB RF output drops down across the entire band after it's been on and heated up for a while. I will look at that more today but mostly its just above channel 16. I am using a Byrd wattmeter into a dummy load.
Any thoughts, recommendations or Devine intervention?

Thanks and 73, ScannerHam62

ps: there are some additional mods. It has a temperature controlled fan on the back, a three level RF power switch on the back and the mic jack has been converted internally to accept Cobra pinouts.

 

[ScannerHam62]

Here a little more info. RF output on SSB changes as you go through the channels. Remember this is into a dummy load with a Byrd Wattmeter. Doesn't seem to matter what mic I use. Channel 1 is 5 watts, CH 5 is 6 watts, CH 10 is 9 watts, CH 12 is 10 watts, CH 14 is 12 watts, CH 15 is 5 watts, CH 16 is 3 watts, CH 18 is 2.5 and it stays at 2.5 all the way through CH40. This is all with a good whistle in the mic. On the upper channels if I pay around with the mic gain and run it way down to the 10 or 9 o'clock position I can get it RF output up to about 5 to 6 watts but it jumps around. Almost like the ALC is kicking in? Curious.

 

[ScannerHam62]

Even more info:
Around channels 12, 13, 14 where the SSB RF output is the highest, the mic gain acts as it should. When the mic gain is all the way up the power is the highest and the RF reduces smoothly as you turn it down. This is the case on the lower channels as well although the RF output is reduced overall. Only when you get above channel 15 - 16 (and higher) does lower mic gain equal more power and seems to jump around a lot as you adjust it. Of course I am speaking of the front panel mic gain control, not anything internal!

 

[ScannerHam62]

Occasionally the SSB RF output drops down across the entire band after it's been on and heated up for a while.

After further investigation the above quote is incorrect. The SSB RF output stays constant. It does not change as the unit heats up. It just varies over the channels as I have described.

 

[ScannerHam62]

I am beginning to think this is an alignment problem? The SSB RF is pretty good on channel 11-12 but then goes down on either side, sharply after channel 16. Also, why would the ALC circuit clip audio on one frequency and not another?
I await the technical masters for comment...…………….

 

[Dmans]

I am beginning to think this is an alignment problem?

ScannerHam62,
You are probably in the right area. Perhaps with weak RF output tubes, a prior owner "tweaked" the output for maximum close to or around the channels he frequented.
Alignment in the center of the band will probably net you even but lower than expected (factory fresh) output.

Good Luck

73
David

 

[ScannerHam62]

Alignment in the center of the band will probably net you even but lower than expected (factory fresh) output.

I'm not sure what you mean by this.

 

[Dmans]

As tubes and components age, output decreases. Alignment with original tubes and components may restore even output power spread albeit lower than the "original factory fresh" D201.

Edit:
Just noticed you said this is a D201A. I've never owned one but I have read reports of the D201A channel selector/switch having less than a stellar reputation. Could be a possible cause of your reduction in output power with increasing frequency.

73
David

 

[nomadradio]

The "black" crystal selector is that color, and the body has square sharp corners. Should be a logo for "A-mp", the vendor on it somewhere.

This is the "poof" switch. It was famous for going bad after only weeks of regular use.

An improved selector was made by Siecor (I think). It has a gray body with rounded corners.

Alignment is probably at the root of these symptoms. A wattmeter worshipper will crank the neutralizing adjustment for max wattmeter reading, making the final unstable. When it oscillates, you'll see power in SSB transmit with the mike gain turned to zero. Also causes odd behavior when modulating sideband.

It's supposed to be set for max stability. The procedure in the manual sucks.

Does suggest to me that there is more than "just one" gremlin behind the symptoms you're seeing.

73

 

[ScannerHam62]

Thanks all for the input. The reason I primarily use the VFO is to keep the crystal selector use to an absolute bare minimum. It works OK right now!

I'm not sure if I want to mess with this unit any more. I may list this "for sale" here.
I haven't adjusted any of the cans.

 

[ScannerHam62]

I know someone is going to ask so...……….$375, but I'd rather not ship it. Its located in Myrtle Beach, SC. At that price I'll be taking a loss on it. I paid $475!