[murf]

Hello again fellas,
Have an issue with my 12S568 Zenith that I just re-capped.
Radio plays well, but after a few minutes it develops a humm.
Increases with volume.
Not noticeable on strong stations, but is there on the weaker stations and in between stations.
Checked all tubes and looked for anything missed or loose under the chassis.
Things has some awesome sound, just need to get rid of the humm.
All 4 E-cap were changed by previous owner. Has 2 22'sx450 and 2 10'sx450. According to the schematic those 2 10's should be 16's.
Would this cause the hum?
Will swap them out, but just curious if this can cause the humming issue?
Take care,
murf

[murf]

Ok,
Swapped them out for 22's instead of the 10's that were in there.
Still humms.
Very annoying when you think your ready to go back in the cabinet.
Any suggestions from you Zenith Pro's ?
murf

[Radioroslyn]

If the hum happens after it's been on for a few minutes and not when you 1st turn it on I would suspect a bad tube. Leakage between the heater to cathode or cathode to control grid could do it. Try removing each tube one by one and listen to hear if the hum goes away. Tubes in the audio output would be a little more likely to be the cause vs the others. Leave the rectifier tube in place, if you remove it the set won't do anything (no hv).

[murf]

Will try it tomorrow Terry,
Thanks
murf

[morzh]

It might even be bad rectifier tube. But most probably the audio tubes.

[murf]

Hi guy's,
Terry was right on.
Pulled the tubes one at a time and found a bad 6K7 tube.
I know it tested ok before.
Pulled the 6J5's first, and got lucky on the 5th tube.
Thanks for the help again guy's.
murf