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Hunting down the short in a Motorola 61CA
#10

I tried it with a 60 watt bulb in place and get a dim glow at 100+ volts (it starts around 85v or so). I kept a volt meter on the CT and after a couple of minutes the voltage was -9v and rising when I cut power. I've replaced the 41 with one of the 41s from my 46-280 set and warmup time should be reduced. All of the tubes test in the 70s or better on all tests at this point. I get a growl from the speaker when I touch the ungrounded side of the volume control with a soldering iron, so I'm guessing whatever the issue is, it is not necessarily in the output section.
Around 90 volts on the variac, I get a hum on the speaker that continues as I apply more voltage.

The only voltage other than the CT I took was the plate of the output which was pretty low, but Like I said, I haven't let the set properly warm up since I popped the small electrolytic cap. When I popped the 22f @50v cap previously, I did not replace the 10uf @ 500v or the 22 uf @ 450v caps. Do you think I might want to do that?

Or should I fire up the signal generator and start in with the grid of the 75 or 6D6?

Charlie in San Antonio


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RE: Hunting down the short in a Motorola 61CA - by ccomer1955 - 08-22-2015, 02:42 PM



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