I have a radio that requires very precise tuning on the station, to avoid oscillation, whistles, distortion, etc. This was not apparent with the radio out of the cabinet and on the bench. I shouldn't be comlaining as it sounds great on the station. Perhaps speaker wires are too close now in the cabinet, and shielding required?

:I have a radio that requires very precise tuning on the station, to avoid oscillation, whistles, distortion, etc. This was not apparent with the radio out of the cabinet and on the bench. I shouldn't be comlaining as it sounds great on the station. Perhaps speaker wires are too close now in the cabinet, and shielding required?

my guess is IF amplifier oscillating. When you are "zero beat" with the station carrier, the oscillation is not heard. I don't suspect speaker wires if the tuning affects the whistle. If it is easy to get to an IF transformer, gently mistune it slightly and see what happens. Be ready to put it back where it was if that doesn't help.
Lewis

What is the radio and do you have the schematic?

Have you fully re-capped it?
Did it ever wok well in the cabinet?

Did the IF alignment seem to peak properly?

Sometimes the antenna leads and especially the local oscillator wiring dress may need to be rearranged... but maybe the components there are drifting in value as well.
Have you checked all the resistors in that area? Also...even though they are seldom a problem mica caps may go bad causing this symptom.
I recently had a "sharp tuning" distortion problem too and I found that the 50pf coupling cap (mica) was leaky... replacing that totally solved my problem.

:I have a radio that requires very precise tuning on the station, to avoid oscillation, whistles, distortion, etc. This was not apparent with the radio out of the cabinet and on the bench. I shouldn't be comlaining as it sounds great on the station. Perhaps speaker wires are too close now in the cabinet, and shielding required?

Hi Brian,
Lewis' advice is good, however, I have something else to try. This problem can be caused by poor grounding on the IF tube shield. Remove the shield or ground it securely with aligator clips. This could explain why it is different in or out of the case.
To implement the fix Lewis described, on each of the two IF cans turn one screw 1/8 turn clockwise, the other 1/8 turn counter clockwise. This should eliminate the off channel birdie. If not eliminated turn them a little more.

My Zenith 5S127 had that problem and now I play it almost every evening and it sounds great.

Best Regards,

Bill Grimm

Bill,

I went back and looked at my shielding in IF stage, all tubes in this radio require shielding (Stewart Warner R400) and I have some misfiting ones that are not original. Sure enough, I grounded the shield with a wire and it cleared up. thanks again.

::I have a radio that requires very precise tuning on the station, to avoid oscillation, whistles, distortion, etc. This was not apparent with the radio out of the cabinet and on the bench. I shouldn't be comlaining as it sounds great on the station. Perhaps speaker wires are too close now in the cabinet, and shielding required?
:
:Hi Brian,
: Lewis' advice is good, however, I have something else to try. This problem can be caused by poor grounding on the IF tube shield. Remove the shield or ground it securely with aligator clips. This could explain why it is different in or out of the case.
: To implement the fix Lewis described, on each of the two IF cans turn one screw 1/8 turn clockwise, the other 1/8 turn counter clockwise. This should eliminate the off channel birdie. If not eliminated turn them a little more.
:
: My Zenith 5S127 had that problem and now I play it almost every evening and it sounds great.
:
:Best Regards,
:
:Bill Grimm