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Post by husker on Dec 9, 2017 23:01:11 GMT -5
I am sure many of you know there are differences between the fixed and non fixed bias versions of this radio. I have been told that Tram produced a "addendum" for the fixed bias versions schematic. If there is such a beast does anyone have it I could see? There seem to be more questions then there are answers and I really need a schematic to try to trouble shoot.
If any one has this item please let me know.
thanks!
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Sandbagger
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Post by Sandbagger on Dec 10, 2017 11:22:46 GMT -5
I am sure many of you know there are differences between the fixed and non fixed bias versions of this radio. I have been told that Tram produced a "addendum" for the fixed bias versions schematic. If there is such a beast does anyone have it I could see? There seem to be more questions then there are answers and I really need a schematic to try to trouble shoot. If any one has this item please let me know. thanks! I think we'd all like to see those. |
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Sandbagger
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Post by Sandbagger on Dec 10, 2017 15:33:31 GMT -5
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Post by husker on Dec 11, 2017 0:14:00 GMT -5
LOL, yes Ron has been helping me try to figure out this crazy radio issue. He got tired of attempting to use the wrong schematic so he decided to reverse engineer the entire thing. VERY nice work!!
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Post by mark4 on Dec 11, 2017 21:31:01 GMT -5
But don’t copy the posted pic of the BA board. It’s not correct. Resistors where jumpers should be etc. |
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Post by husker on Dec 22, 2017 12:57:23 GMT -5
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Sandbagger
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Post by Sandbagger on Dec 22, 2017 14:33:22 GMT -5
I am way past confused at this point. I have been struggling with this 201a now for well over a month. To the point of almost giving up. The radio is a fixed bias 201a(see attachment). If i use the correct BA brd (jumpers not resistor etc) the final audio tube cherries withing 2 min. If i use a NON fixed bias BA board it works fine. (Except still don't have AM audio, but SSB works fine) I also have another 201a that is 100% stock, is fixed bias and runs the same non fixed bias BA rd. Now I am 1000% confused.. View AttachmentIf you have receive audio on SSB, but not AM, then the problem lies in the AM circuit (or mode switch), not the audio board itself. Although there are still some issues that need to be addressed concerning the biasing of the final tube. |
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Post by husker on Dec 22, 2017 15:43:13 GMT -5
The final audio tube? It is set at 35v at pin 5. According to what I have read, that's correct. Agreed? lol... I have also replaced r322 to make sure it wasn't the issue on receive. It was older. not factory, but older so I replaced it as well.
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Sandbagger
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Post by Sandbagger on Dec 22, 2017 16:09:30 GMT -5
The final audio tube? It is set at 35v at pin 5. According to what I have read, that's correct. Agreed? lol... I have also replaced r322 to make sure it wasn't the issue on receive. It was older. not factory, but older so I replaced it as well. There should be a ~30V difference between the cathode (pin 8) and the control grid (pin 5). If the radio is set up like the D201 (self bias), then there should be +31V on pin 8 and less than a volt on pin 5. If it is set for the later "fixed bias" then you should have 0V on pin 8, and -31V on pin 5. 35V on pin 5 is ok as long as it's a NEGATIVE 35V. But please confirm. Do you have receive audio on SSB? That changes things if so. |
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Post by husker on Dec 22, 2017 16:18:22 GMT -5
Yes it is negative. And yes, great receive audio on SSB.
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Sandbagger
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Post by Sandbagger on Dec 22, 2017 20:51:29 GMT -5
Yes it is negative. And yes, great receive audio on SSB. Well, if SSB receive audio is good, then the audio amplifier section is working (at least somewhat). You SHOULD also have AM transmit modulation. No AM receive audio could be several things. Do you see signals on the S-meter on AM but just not hear anything? Or is the receiver completely dead on AM? The answers to those questions could give clues as to where to look for a problem. A dead AM-only receiver could be due to the failure of R322, a common issue where the resistor opens up due to long term current draw. There could be other issues as well. But since SSB is working, you can rule out all of the stages that are common to both modes. So you're left with the AM IF stages and the detector. If you have AM receive showing on the S meter but no audio, you might have bad solder joints or corrosion on the connections to the "AA" board where the detector circuit is or on the mode switch. |
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Post by husker on Dec 22, 2017 22:44:30 GMT -5
SSB receive is fine, AM receive is very weak, I have to turn the volume up almost all the way. And the S meter is great on SSB, no movement on AM
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Post by 2600 on Dec 22, 2017 23:15:25 GMT -5
Check pin 6 of V400, the 6BA6 tube for at least 85 Volts DC. If it's much higher than 100, that's wrong.
If it's way low, find R402, the 47k resistor that feeds pin 6. The other end of it should show about 240 Volts DC.
If it does, R402 is probably bad.
If not, R403, a 2.2k resistor that feeds into it could be bad.
Making sure you have a proper peak in each slug of T302, T400 and T401 is important. The single slug in L400 matters, too.
But clearly, the problem is in an AM-only circuit downstream from where the AM and SSB receiver signals branch off separately.
73
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Post by husker on Dec 22, 2017 23:52:16 GMT -5
Check pin 6 of V400, the 6BA6 tube for at least 85 Volts DC. If it's much higher than 100, that's wrong. If it's way low, find R402, the 47k resistor that feeds pin 6. The other end of it should show about 240 Volts DC. If it does, R402 is probably bad. If not, R403, a 2.2k resistor that feeds into it could be bad. Making sure you have a proper peak in each slug of T302, T400 and T401 is important. The single slug in L400 matters, too. But clearly, the problem is in an AM-only circuit downstream from where the AM and SSB receiver signals branch off separately. 73 I just checked the resistors you listed real quick, both check good. I will test voltages on the tube. Ok, pin 6 is 102vdc. The other side of R402 is 245vdc but v301 pin 6 is 182vdc? seems rather high |
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Post by 2600 on Dec 23, 2017 1:23:37 GMT -5
The high reading at pin 6 of V301 could be from R307 getting old and the resistance value dropping with age. We routinely replace it with a 2-Watt ceramic-body resistor without bothering to check it first.
But this reading is upstream from where the SSB and the AM signals branch off into separate directions. Since it's not holding back the SSB receive side, it's not the culprit for poor AM sensitivity. Might check pin 1 of V302. If it's way below 130 Volts, suspect R310, maybe R311, maybe both. This is the first AM-only voltage reading downstream from the AM/SSB split.
73
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Post by husker on Dec 23, 2017 1:43:45 GMT -5
The high reading at pin 6 of V301 could be from R307 getting old and the resistance value dropping with age. We routinely replace it with a 2-Watt ceramic-body resistor without bothering to check it first. But this reading is upstream from where the SSB and the AM signals branch off into separate directions. Since it's not holding back the SSB receive side, it's not the culprit for poor AM sensitivity. Might check pin 1 of V302. If it's way below 130 Volts, suspect R310, maybe R311, maybe both. This is the first AM-only voltage reading downstream from the AM/SSB split. 73 Both r310 and r311 check out good. V302 pin 1 was 121vdc. The no S-meter is also related correct? |
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