D201 HW modulation problem

[igon71]

This is my first post. I just recently obtained my first Tram D201. I have many Brownings, but this is my first Tram. Everything works and the radio is in pretty good shape, but I have very low modulation. I checked all the tubes and replaced the weaker ones with new. I change all the tubes for the modulation with new also. With the mic gain all the way up, I am only getting 60% modulation. I am using a UG-8 D104. I have tried a few of my other straight D104's with no change in modulation. All the electrolytics have been changed. I can only get maybe 2 1/2 watts out of it also. I need some advice on where to look or what to check next from some of you seasoned Tram owners.

[Marc]

My D201 is a PCB ver but had a prob similar to yours.

I found that the tube sockets for the 6GH8A tubes in the audio section were not making good contact(old and stretched) had to bend the legs of the tubes out just a little to make good contact.

When it would loss contact my audio would drop off and would loss a watt or two.
If that fixes the prob you need to change the sockets

Just a thought

Marc

[FIXR]

Check the voltages on V601A. There are a couple of 47K and a 470K 1/2 watt resistors that sometimes change value.
If that tube checks OK, go to the next 6GH8A, V600A and check there. V602A would be next after that, but if the receiver volume is OK it is probably OK also.

Fixr

[igon71]

Wow, your responses were very fast and I thank you. I wish I could have responded sooner but I have too many things goin on here all at once. First, I was extremely surprised on how tight the tubes fit in the sockets. So I don't believe that is a problem, but thanks anyway. I've found a Sams CB-88 and it is on it's way to me as I am writing this. Fixr, I thank you also for your suggestions and will do exactly as you described and will post my results, but without the Sams I don't know what the voltages should be. The other thing that I noticed is that I had a hum coming out of the speaker and after changing the 6GH8's with new it was gone but only temporarily. It came back aftyer a few hours. Now no matter what I do now it won't go away. What do those tubes have to do with the receive? I didn't think anything? Please correct me if I'm wrong. I changed those tubes with another new set and it still persists. Sounds like a cap somewhere to me. Boy, do I need that schematic now. A day or two more and I'll have it.

[2600]

Loose tube sockets are mainly associated with the pc-board versions of the D201. The sockets that are made to mount in the metal chassis just don't go bad this way, as a rule. The sockets used on the pc boards are made differently.

This is one reason that the original-version open-chassis style ("hand-wired") D201 is more popular than the later ones with the large pc boards If they feel tight when removing and inserting the tube, they're probably okay. A shot of non-residue cleaner can be helpful if a tube socket develops "Rice Krispy" problems when the tube is nudged a bit.

The hit parade for bad resistors that reduce your transmit audio would be R620, a 470k on pin 3 of V601. Next would be R646, a 330k 1/2 Watt. It feeds one end of the AM limiter trimpot R647.

If the receiver audio is also a bit weak, R635, a 47k 1 Watt is worth checking.

And if the original electrolytic caps are still in this radio, C625 and C621 would be suspect. They will also affect the receiver audio, as a rule.

ANY AND ALL factory-original electrolytic capacitors are way, way past their intended design lifespan. They will be breaking down one or two at a time until you get tired of it and replace ALL of them.

Yes, I said ALL of them. It's not just the miles, it's the years, too.

And some folks consider it fun to have the radio break down every week or three, so they can track down which electrolytic cap (or two) has failed THIS time. If you do it that way, eventually all of them will get replaced. Eventually.

73