Zenith 6S-229 Question

[sgtrob]

Hello everyone! I have a bit of a peculiar problem with my Zenith 6S-229 chassis. The DC seems to drop drastically across the fileld coil for the speaker, nearly killing all the DC. The input voltage at the speaker socket (for the field coil at C16) is about 250 VDC. But on the other side of the coil, which is consequently also the input for the Audio output transformer at C17, the voltage has dropped to only about 34 VDC. The speaker also doesn't seem to magnetize when powered. I checked the field coil continuity, it is at 1245 ohms, near what the schematic said it should be. Could it be shorting out when I apply power? I aready replaced the main filter caps. ANY advice is most welcome! -Rob

[jeyurkon]

According to the schematic on Nostalgiaair, you should be seeing about 322V at C16 instead of 250V.

I think you'd expect to see that and the 34V at C17, if C17 was shorted. You might want to check to see that you installed it with the correct polarity and that it is good. That wouldn't explain the apparent lack of field of the magnet though.

John

[sgtrob]

Just checked the polarity of the filter, and replaced it, just to be sure. Still have the same voltage indications. Also for some reason the speaker field is getting incredibly hot . -Rob

[jeyurkon]

Did you replace all of the paper caps? If not, you need to do that.

In particular, if C5 were shorted you would have that problem.

I don't think a shorted field coil would cause it to get hot. Only if the field coil were shorted to the frame and the frame was in turn connected to the chassis ground would that be the cause.

The schematic shows two C5 capacitors which is a bit confusing.

John

[radio63]

Rob,

Sounds like you have further shorts in your radio. Replace all bypass caps and in particular paper caps in the audio output stage. Look for shorted wires, or obvious signs that there's a short circuit. A short in one of the tubes would cause a problem too.

Sounds like the short is drawing too much current through the field coil causing it to overheat. Let us know what happens when you get the caps changed out.

Gilbert

[Chimes]

Pull the 6F6 audio output tube and see if the voltage still drops. If it does, check C5 (.05). Make you check quickly (seconds) as with a voltage drop of 216 volts across the speaker field coil, it is drawing over 170 milliamps and won't last long. That is why it is getting hot.

[Chimes]

So did you find the problem?

[sgtrob]

Sorry for the delay, had to run to the east coast. Gonna jump back into the Zenith tonight. Will let you know what I find! -Rob