I have been working on a Zenith 6s511. All the usual, caps/ecaps, resistors, some wiring replaced. Set plays and has good selectivity. Has a non tunable hum on both bands. Hum does not increase with volume.
So checked plate voltage on 6x5 rectifier. Calls for 225v each plate and I have 250 and 160 with the 6x5 pulled. My thinking is power transformer going bad. Looking for confirmation or other thoughts.
Schematic: http://www.nostalgiaair.org/PagesByModel/230/M0025230.pdf
Thanks for any insight.

250 volts doesn't seem to be out of the ballpark. If the transformer isn't blazing hot it is probably OK.
You might check the 42 ohm wirewound resistor R14. If this resistor is out of spec it will screw up the HV reading (because it references the transformer HV center tap to chassis ground).

If the hum is present when the volume control is set at minimum, check the installation of the two electrolytic caps in the set. Polarity must be correct (- goes to each side of the speaker field coil, + on both tie together and go to the rectifier cathode pin). If you find that one or both cap has been polarity-reversed, it will need to be replaced.

" If you find that one or both cap has been polarity-reversed, it will need to be replaced. "

To clarify, don't just remove, reverse, and reinstall the same cap. Chuck it and install a fresh one. The old one is toast if it was reverse-biased.

Thanks CV. I was more concerned about the plate voltage being too low. I guess I should have included that under load rectifier plate pin3 is 230v and pin5 is 160. Also the plate and grid voltage is low throughout set. And yes after about half an hour this sets power transformer gets mighty hot.
I will check the issues mentioned.

So, basically what you have is a unbalanced power transformer- one half of the winding is putting out considerably more voltage than the other half. There's a tiny chance that the 6X5 rectifier tube is faulty, but much more likely is that you have a shorted winding in the power transformer.

:So, basically what you have is a unbalanced power transformer- one half of the winding is putting out considerably more voltage than the other half. There's a tiny chance that the 6X5 rectifier tube is faulty, but much more likely is that you have a shorted winding in the power transformer.

CV:
He pointed out that the readings were taken with the 6X5 pulled. It sure sounds like shorted windings in the secondary of the power transformer.

Lewis
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250/160 with rectifier tube pulled.
230/160 with rectifier tube in place.

Looks like a bad transformer. Fortunately, this is a fairly simple one- relatively low-power, and only two secondaries.

Yup, that is what I was thinking. Thanks for the confirmation.

With that much difference in voltage should be easy to check the transformer. Let it operate for 30 minutes. It should be very hot or smoking.

Norm

:Yup, that is what I was thinking. Thanks for the confirmation.
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I picked up a replacement transformer. Instead of the original 225 0 225v the replacement is 245 0 245v. Opinions on whether this will necessitate use of added resistance?

Probably. Assuming that your electrolytic caps are rated high enough to withstand the slightly higher voltage, you can wire the new transformer in and measure what your B+ current draw and voltage are as it stands, then you can compute the value/power rating of a dropping resistor to knock the B+ back down to spec.