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TRAM D201 non hand wired low AM Recieve

C

Crambone

Well-Known Member
Jan 22, 2019
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I have a D201 that is showing low AM Receive but USB & LSB are great. The radio keys 4watts and swings 12 with great modulation. I checked all the tubes and they all show 95-100% on my Sencore VII.
I tried doing a 455 Hz AM Alignment as T400 was replaced due to a broken slug. Following procedure i fed 455Hz to pin 2 of V302 with a .01uf cap between. I good good adjustment on the L400 but none on T400 or 401 it makes zero change?
Now what?
 

If those two won't show a peak, I would suspect the capacitors inside those two cans.

The polystyrene capacitors inside T400 and 401 are known to go bad, especially if the radio was run hot, or had a lot of mileage. Polystyrene caps are great until they get too hot.

The original caps are 330 pf, one inside the can each parallel to one winding. If you can find a silver mica cap small enough to fit, they're a good choice. We use a 390pf polystyrene cap because I stumbled across a bag of them years ago, and they're small enough to fit. The higher capacitance value doesn't seem to affect how well the slugs will peak when adjusted.

I'll guess you checked DC voltages on the 6BA6 and the 6GH8 in the AM receive.

73
 
nomadradio said:
If those two won't show a peak, I would suspect the capacitors inside those two cans.

The polystyrene capacitors inside T400 and 401 are known to go bad, especially if the radio was run hot, or had a lot of mileage. Polystyrene caps are great until they get too hot.

The original caps are 330 pf, one inside the can each parallel to one winding. If you can find a silver mica cap small enough to fit, they're a good choice. We use a 390pf polystyrene cap because I stumbled across a bag of them years ago, and they're small enough to fit. The higher capacitance value doesn't seem to affect how well the slugs will peak when adjusted.

I'll guess you checked DC voltages on the 6BA6 and the 6GH8 in the AM receive.

73
Click to expand...
I didn’t check the voltages off the tubes I will do that next.
 
Think they would fit?

E68BD6AC-8D19-4096-9023-C5E4B42E8A24.png
nomadradio said:
If those two won't show a peak, I would suspect the capacitors inside those two cans.

The polystyrene capacitors inside T400 and 401 are known to go bad, especially if the radio was run hot, or had a lot of mileage. Polystyrene caps are great until they get too hot.

The original caps are 330 pf, one inside the can each parallel to one winding. If you can find a silver mica cap small enough to fit, they're a good choice. We use a 390pf polystyrene cap because I stumbled across a bag of them years ago, and they're small enough to fit. The higher capacitance value doesn't seem to affect how well the slugs will peak when adjusted.

I'll guess you checked DC voltages on the 6BA6 and the 6GH8 in the AM receive.

73
Click to expand...
 
nomadradio said:
If those two won't show a peak, I would suspect the capacitors inside those two cans.

The polystyrene capacitors inside T400 and 401 are known to go bad, especially if the radio was run hot, or had a lot of mileage. Polystyrene caps are great until they get too hot.

The original caps are 330 pf, one inside the can each parallel to one winding. If you can find a silver mica cap small enough to fit, they're a good choice. We use a 390pf polystyrene cap because I stumbled across a bag of them years ago, and they're small enough to fit. The higher capacitance value doesn't seem to affect how well the slugs will peak when adjusted.

I'll guess you checked DC voltages on the 6BA6 and the 6GH8 in the AM receive.

73
Click to expand...
Ok I checked voltages and something is definitely off with V401

V400
Pin. Schematic. Reading
1. .2V. .3V
2. - -
5. 245V. 248V
6 109V. 113V
7. 2.5V. 2.4V

V401
2. .2V. 0V
3 95V. 269V
7. 2.1V. 17V

1. 119V
4. 0V
5. 0V
6. 272V
8. 1.2V
9. 0V
 
I’m looking at the schematic and comparing to the board I noticed the only 2 resistors that aren’t factory are 405 and 406 that both are 47k. The schematic calls for R405 220ohm and R406 2.2K ohms. Now I’m not sure if I have the correct schematic? This is the non hand wired D201.
 
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There is a parts-placement diagram on cbtricks.com in the manual for the 23-channel circuit-board version of the radio. It's on page 23.

http://www.cbtricks.com/radios/tram/d201/index.htm

The schematic posted along with that manual is not the right one. What's posted alongside the manual for the circuit-board radio is the schemo for the VOX version, the previous production to the one you have.

Bennie didn't quite get that section right, and the closest schematic posted there is for the 40-channel radio.

One end of R405 is connected to pin 7 of V401. If R405 really is 47k, then that's a mistake. You won't have any AM receive until it gets changed to the correct 220 ohms.

One end of R406 connects to pin 3 of V401. A 47k in place of the correct 82k would not create such a large problem, but might make V401 run too hot.

Not sure how the wrong parts would end up in those two spots. Double-check against the parts-placement diagram to see you have identified those two parts correctly before changing them. The voltage you show for pin 7 of V401 is right. If R405 really were 47k, it would read a lot higher.

I still think you have trouble inside T400 and T401. When they fail, the capacitors inside those two cans will disrupt the circuit's signal gain, but won't affect any of the DC-voltage measurements. Your DC meter will say everything is fine, but you won't have any signal.

73
 
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Thank you soooo much I will double check those parts today.
Do you know if an accurate schematic exists for this version D201? SAMS Photofacts?
 
Sams volume CB-88 only shows the original open-chassis ("hand-wire") version of the radio. Yours is the later 23-channel radio with big printed-circuit boards on the right and left of center.

Still haven't found a decent copy of your radio's schemo online.

The later 40-channel D201A diagram is on CB Tricks, along with the earlier "VOX" version, built with all the tube sockets mounted to holes punched in the metal chassis deck.

The 23-channel circuit-board built radio is a "schematic orphan", unless you find someone on Ebay or such selling a paper copy.

73
 

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