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#1
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IDK if the volume control is a log or a linear taper. Also, the schematic shows a 250ohm resistor in series, but the parts list shows that the resistor is part of the control. Some experimenting is needed! Re: the next entry problem with the hum, maybe the 6J7 or the 6F6 has an H-K short. Sure is one for the books. |
#2
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I cannot for the life of me imagine how just changing the power cord would cause a very loud 60-Hz hum as you are describing; after all, the power cord itself should not have any effect whatsoever on the audio output. If the radio had been working up to now, the only thing I can come up with is a heater-cathode short in one of the audio tubes. Given this radio is very old (pre-WWII vintage), that would not surprise me in the least. Vibration from moving the chassis could have caused such a short, especially if the tube were about to develop an H/K short eventually.
I would not operate the radio in its present condition if it does not have an AC line fuse (it is my understanding that most pre-war radios did not have such a fuse, which all too often led to very serious trouble if a tube were to develop an H/K short or a filter cap would short the same way). The house fuse might blow in case of a shorted tube or filter capacitor, but I wouldn't count on it.
__________________
Jeff, WB8NHV Collecting, restoring and enjoying vintage Zenith radios since 2002 Zenith. Gone, but not forgotten. |
#3
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I think I figured out what happened, I think the volume control pot is what's causing the radio to hum, because I think the volume control pot (which was already sketchy when I had gotten the radio going) finally went to "pots" (pun intended) when I attempted to clean the volume control pot with contact cleaner to see if I could restore the volume control's functionality again (because as I had mentioned before the volume control pot when it was working before it apparently finally failed would cut in and out depending on where the volume contol was rotated.) Does any one on here have any known working volume controls with a built in power switch that they could send me? |
#4
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Check it with all the leads disconnected and see if it reads the same. Remove it from the chassis and look inside. All kinds of strange goings on with that set. |
#5
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OK Will do.
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Audiokarma |
#6
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I've seen non-AVC superhet radio circuits, but that one is a real gem.
I repaired the one I have or had, but I just replaced the bad caps and never realized that the set was that strange! |
#7
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I located that chassis in my collection. I'm not sure if I have the cabinet, so I don't want to part it out.
It sure is a strange beast! |
#8
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how is yours wired up?
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#9
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I ohmed out the volume control pot just to make sure it was still good and it was only measuring 1 ohm all across the pot no matter where the volume control knob was set, which tells me that the volume control pot has failed and is perhaps what is causing my humming problem, because the volume control is grounded to chassis using the left side terminal and goes to the kathode of the 6A8 tube from the middle and right side tap of the volume control pot. Is there any way to test this theory by somehow taking the volume control pot out of the circuit? Last edited by vortalexfan; 07-10-2021 at 07:23 PM. |
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