I have posted about this problem before. many years ago. The amplifier will go suddenly loud and distorted in one channel and have a very very quiet signal (only audible when loud channel is not connected) in the other. I am positive its not the OT
Grounding the input temporarily will some time make it go away. I have checked, replaced and rebuilt everything in the signal chain but it wont go away. works fine for hours and then suddenly loud and distorted in one channel.
I now believe that the fault is in the can capacitor after the rectifier. Its the only thing I can blame. i believe that there is some leakage of current between the two capacitors in the can. It would explain the all the symptoms. I am a few hours from being able to try this solution and thought i might float this idea for comment http://www.44bx.com/leak/Leak/Circuits/Stereo20.gif
Grounding the input temporarily will some time make it go away. I have checked, replaced and rebuilt everything in the signal chain but it wont go away. works fine for hours and then suddenly loud and distorted in one channel.
I now believe that the fault is in the can capacitor after the rectifier. Its the only thing I can blame. i believe that there is some leakage of current between the two capacitors in the can. It would explain the all the symptoms. I am a few hours from being able to try this solution and thought i might float this idea for comment http://www.44bx.com/leak/Leak/Circuits/Stereo20.gif
Like kokoriantz, I'm sure the can caps are not causing this problem.
And like kokoriantz again, I would guess that the feedback loop is prime suspect.
The picture shows how it is wired on a Stereo 20. Blue wires from the OP transformers (16 ohm feedback tap) to the board corners. From there, at the back of the board, are pink wires connecting to the R18L/R, then from R18 to the junction of R3L/R and R4L/R. A broken wire or poor connection on any of these points would cause loss of feedback and the symptoms you describe. Have a careful inspection and re-flow the solder at these points first.
Alan
And like kokoriantz again, I would guess that the feedback loop is prime suspect.
The picture shows how it is wired on a Stereo 20. Blue wires from the OP transformers (16 ohm feedback tap) to the board corners. From there, at the back of the board, are pink wires connecting to the R18L/R, then from R18 to the junction of R3L/R and R4L/R. A broken wire or poor connection on any of these points would cause loss of feedback and the symptoms you describe. Have a careful inspection and re-flow the solder at these points first.
Alan
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Thanks for the reply. i have already checked that. As i stated i have completely rebuilt this some years ago. also this wouldnt affect both channels. One channel will go an order of magnitude louder AND the other will go extremely quiet, at the same time, completely randomly.
I will go have another look and see what emerges
Thanks again
I will go have another look and see what emerges
Thanks again
That is odd then.
Is it the same channel that goes quiet every time or does that swap from side to side too?
The only 'shared' part between the left and right channels is V1 (ECC83). And I expect you have replaced that.
Maybe look closely at the V1 for loose socket pins and the socket itself for 'tracking'.
'Off the wall' if V1 lost connection to either pin 4 or 5, one side of the heater would go off and cause a quiet side, but how it makes the other louder???
Alan
Is it the same channel that goes quiet every time or does that swap from side to side too?
The only 'shared' part between the left and right channels is V1 (ECC83). And I expect you have replaced that.
Maybe look closely at the V1 for loose socket pins and the socket itself for 'tracking'.
'Off the wall' if V1 lost connection to either pin 4 or 5, one side of the heater would go off and cause a quiet side, but how it makes the other louder???
Alan
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