any suggestions?
Thank you,
vinny
Seems like to me, that the highest probability for the problem is to be associative with the audio output circuits two coupling capacitors or the output tube itself. With it either being gassy, or developing grid emission.
After a reconfirmation of ZERO DC leakage, on those 2 specific capacitors, try this additionally.
Turn on the cold radio and run the volume down to zero and then take a ground referenced DC measurement of the negative grid bias on the output tubes first grid and log it. Then run up the volume and play the unit until your perceived degradation of the sound FULLY onsets. Then you drop the volume back down to zero again and measure the first grid voltage again and see if the first grid voltage has now become less negative than the initial reading then you can certainly suspicion that output tube being bad with temperature onset.
Reference Schematic Thumbnail:
73's de Edd
I am a 53 year old beginner. I learned over night how to test for capacitance on a new Radio Shack multimeter and I am going to test the new one's that I have installed. According to the literature (antique radio restoration guide) that I have recently read, one leg of the capacitor should be disconnected, is this true? Also, the 50L6GT tube was replaced by the 50A5 tube, according to page 1 of the schematic. Without beating around the bush, how do I test for negative voltage? Which pin(s) do I use and do I use the chassis as a ground?
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:Seems like to me, that the highest probability for the problem is to be associative with the audio output circuits two coupling capacitors or the output tube itself. With it either being gassy, or developing grid emission.
:
:After a reconfirmation of ZERO DC leakage, on those 2 specific capacitors, try this additionally.
:
:
:
:Turn on the cold radio and run the volume down to zero and then take a ground referenced DC measurement of the negative grid bias on the output tubes first grid and log it. Then run up the volume and play the unit until your perceived degradation of the sound FULLY onsets. Then you drop the volume back down to zero again and measure the first grid voltage again and see if the first grid voltage has now become less negative than the initial reading then you can certainly suspicion that output tube being bad with temperature onset.
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:Reference Schematic Thumbnail:
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:73's de Edd
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Thank yoy,
Vinny
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:Seems like to me, that the highest probability for the problem is to be associative with the audio output circuits two coupling capacitors or the output tube itself. With it either being gassy, or developing grid emission.
:
:After a reconfirmation of ZERO DC leakage, on those 2 specific capacitors, try this additionally.
:
:
:
:Turn on the cold radio and run the volume down to zero and then take a ground referenced DC measurement of the negative grid bias on the output tubes first grid and log it. Then run up the volume and play the unit until your perceived degradation of the sound FULLY onsets. Then you drop the volume back down to zero again and measure the first grid voltage again and see if the first grid voltage has now become less negative than the initial reading then you can certainly suspicion that output tube being bad with temperature onset.
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:Reference Schematic Thumbnail:
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:73's de Edd
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Vinny
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:Seems like to me, that the highest probability for the problem is to be associative with the audio output circuits two coupling capacitors or the output tube itself. With it either being gassy, or developing grid emission.
:
:After a reconfirmation of ZERO DC leakage, on those 2 specific capacitors, try this additionally.
:
:
:
:Turn on the cold radio and run the volume down to zero and then take a ground referenced DC measurement of the negative grid bias on the output tubes first grid and log it. Then run up the volume and play the unit until your perceived degradation of the sound FULLY onsets. Then you drop the volume back down to zero again and measure the first grid voltage again and see if the first grid voltage has now become less negative than the initial reading then you can certainly suspicion that output tube being bad with temperature onset.
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:Reference Schematic Thumbnail:
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:73's de Edd
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:Edd: as a test, can I put a 5oL6GT tube back in the radio from another radio as a test? The schematic says that that tube was replaced by 50A5 tube.
:Vinny
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::Seems like to me, that the highest probability for the problem is to be associative with the audio output circuits two coupling capacitors or the output tube itself. With it either being gassy, or developing grid emission.
::
::After a reconfirmation of ZERO DC leakage, on those 2 specific capacitors, try this additionally.
::
::
::
::Turn on the cold radio and run the volume down to zero and then take a ground referenced DC measurement of the negative grid bias on the output tubes first grid and log it. Then run up the volume and play the unit until your perceived degradation of the sound FULLY onsets. Then you drop the volume back down to zero again and measure the first grid voltage again and see if the first grid voltage has now become less negative than the initial reading then you can certainly suspicion that output tube being bad with temperature onset.
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::Reference Schematic Thumbnail:
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::73's de Edd
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