04-29-2023, 08:49 PM
Intermittents- the nightmare f any mechanic, technician, engineer, etc.!
One interesting observation, you have 2 of these and when you replaced the e-cap and 2 wax caps the same issue occurs. Did the other radio play correctly until the caps were replaced?
If you have an o-scope or a DVM that can read AC ripple, measure the junction of C10 and R4 Does the ripple increase as the plate voltage drop? Does the same thing happen on the other side of R4 (the side that connects to R3 and the 2nd Lytic? Either the caps are funky (like a bad batch) or something is loading it down.
Another interesting point is that the 36V supply is not just to the RF amp plate and screen, it is to the IF amp screen.
If the other radio played well till you changed its lytic, reinstall the originals one at t time (if you have them). Whatever fixes it, do to the first radio.
One other trick would be to remove the 12SK7 and bridge the heater connections with an 80 Ohm 5W resistor, then connect a wire antenna to the stator of the convertor section of the tuning cap, essentially making it a 5 tube radio. If the issue still exists, the RF Amp is not the issue.
But If I read all the posts correctly and you had another working radio that exhibited the same issues after you replaced the caps, then Occam's razor indicates that a batch of bad caps may be the issue.
Finally, are the caps connected to the exact same points (not schematic-wise but physically. Is the common negative of the 2 caps connected to the exact same point on the negative bus?
Good luck!!
One interesting observation, you have 2 of these and when you replaced the e-cap and 2 wax caps the same issue occurs. Did the other radio play correctly until the caps were replaced?
If you have an o-scope or a DVM that can read AC ripple, measure the junction of C10 and R4 Does the ripple increase as the plate voltage drop? Does the same thing happen on the other side of R4 (the side that connects to R3 and the 2nd Lytic? Either the caps are funky (like a bad batch) or something is loading it down.
Another interesting point is that the 36V supply is not just to the RF amp plate and screen, it is to the IF amp screen.
If the other radio played well till you changed its lytic, reinstall the originals one at t time (if you have them). Whatever fixes it, do to the first radio.
One other trick would be to remove the 12SK7 and bridge the heater connections with an 80 Ohm 5W resistor, then connect a wire antenna to the stator of the convertor section of the tuning cap, essentially making it a 5 tube radio. If the issue still exists, the RF Amp is not the issue.
But If I read all the posts correctly and you had another working radio that exhibited the same issues after you replaced the caps, then Occam's razor indicates that a batch of bad caps may be the issue.
Finally, are the caps connected to the exact same points (not schematic-wise but physically. Is the common negative of the 2 caps connected to the exact same point on the negative bus?
Good luck!!
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
