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Problem is SOLVED and I may be a complete idiot ! MORZH - I went away over the weekend with my family and kept thinking about this freakin radio the entire time. Amongst other things - you mentioned: "The resistor in the middle is an NTC thermistor, it starts at about 1K and drops to 100 Ohm as it heats up". I retraced all the caps I installed and checked all the wiring. In my first restoration of this same radio, I noticed that I left the thermistor (see picture) in place because, at the time, I didn't know what it was and didn't want to mess with it. In this most recent restoration, due to me misreading the "chassis - bottom view", I wrongly thought it was a capacitor and replaced it with a .1uf CAP. I thought the thermistor was just a weird looking capacitor. When I got back from my trip, I re lookeded at the chassis diagram and realized what I had done. I soldered out the cap and put back in the thermistor - and VOILA - it popped to life - the tubes, the bulb. So in the end, there was nothing wrong with the on/off switch. I hooked up the speaker and the antenna and already it can pick up some am stations but I will still have to align it. You really nailed the problem - so THANK YOU for your help. Also, thanks to BrendaAnnD for jumping in with your help as well.
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To me those thermistors, which Philco marketed as a "Tube Saver", look more like an old fashioned radial lead resistor then a capacitor. In any event when I was a teenager I had a Sentinel that was working on, so I poked around under the chassis with an ohm meter and found out what I thought was a leaky mica capacitor, which I then removed. However when I tried powering the set up it did nothing, even though the tubes all lit up. It turned out that the leaky mica capacitor was the choke resistor in the B+ supply. But it was not too surprising that I was confused, a resistor that was packaged to look like a capacitor, but Micamold was a lousy company for doing things like that anyhow, like making wax paper caps look like mica caps, all of which were rubbish.
Regards
Arran
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They even made resistors looking like mica caps. Dealt with one myself.
Really dumb idea....as if troubleshooting itself is not confusing enough.
Posts: 122
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City: Coral Springs, FL
(10-12-2014, 08:26 PM)morzh Wrote: They even made resistors looking like mica caps. Dealt with one myself.
Really dumb idea....as if troubleshooting itself is not confusing enough.
morzh & arran -
OK - so now at least I feel a little better that I'm not the only one to have made this type of mistake. Thanks guys !