Author Topic: "Drift compensating" capacitor  (Read 1213 times)

TC Chris

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"Drift compensating" capacitor
« on: March 02, 2016, 11:53:02 PM »
The discussion of ceramic capacitors and their temperature-dependent values brings up a related topic.  I'm working on a 1940 Silvertone radio (AM/SW) that has a burned up metal device in it that looks like an electrolytic cap.  In the Rider's and on the parts list inside the cabinet all the capacitors have their values given EXCEPT this one.  It is described a "drift compensating condenser."  No value is given.  It's in the oscillator circuit.  It's not likely an electrolytic.  The outside can is bullet-shaped.   Another guy on the ARF had made a similar inquiry a year or so ago about his Silvertone and neither his inquiry nor mine turned up any knowledge of WTF this thing is. 

Does anybody know anything about the mysterious "drift compensating condenser"??

Chris Campbell

electra225

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Re: "Drift compensating" capacitor
« Reply #1 on: March 03, 2016, 09:13:17 AM »
What is the model number of the Philco you're working on?
If it ain't broke, call me.  I can break it....

TC Chris

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Re: "Drift compensating" capacitor
« Reply #2 on: March 03, 2016, 06:53:36 PM »
Not a Philco--it's a Silvertone.  They seemed to have liked these odd devices.  The model is R81 and the chassis no. is 101-613.  NostalgiaAir has the schematic but you have to look at the right chassis no. because the model no. applied to a couple different chassis.  The device is C-16.  The parts list inside the cabinet gives the values for each capacitor except this one, which is described only as "drift compensating condenser."  Period, end of story.  No values And all I have is the metal parts remaining after whatever else was there burned up.  It's that odd, bullet shaped thing in the attached photo, about in the center--gray metallic colored, running to chassis ground at the left end and the osc. coil at the other.

Chris Campbell

electra225

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Re: "Drift compensating" capacitor
« Reply #3 on: March 03, 2016, 10:24:24 PM »
I could swear I read "Philco."  Sorry for muddying the waters. 
If it ain't broke, call me.  I can break it....

electra225

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Re: "Drift compensating" capacitor
« Reply #4 on: March 03, 2016, 11:37:16 PM »
The schematic for your Silvertone is in Riders 12 page 4.  That is the only capacitor on that schematic that the value is not given.  I think I'd replace it with a .02 to .05 630 volt film cap and move on.  After I found out what cooked it, I might even lift one end of the old cap and see how the radio performed.  I have an R101 which is the schematic right under yours.  It has that compensating cap in it, too.  I'm not sure of the purpose or what would happen if it was not there, nor how critical the value is.  If it was uber-critical, one would think that the value would have been listed.  Sorry I can not be of more help.  Good luck.
If it ain't broke, call me.  I can break it....

TC Chris

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Re: "Drift compensating" capacitor
« Reply #5 on: March 04, 2016, 12:20:37 AM »
If you've ever got yours out of the box, snap a photo of the mystery cap in an un-burned state.

I've ordered up some filter caps for the radio so eventually I'll be able to see if it functions at all without the drift compensator.  Problem is, I forgot to order new safety caps.  You can see C35-C36 at the top of the photo in mine, a line filter that looks like the next candidate for self-incineration.

Chris Campbell

Consoleman

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Re: "Drift compensating" capacitor
« Reply #6 on: March 04, 2016, 06:55:14 AM »
I think this is your condenser:  http://www.freepatentsonline.com/2179417.html
Mark

TC Chris

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Re: "Drift compensating" capacitor
« Reply #7 on: March 04, 2016, 06:45:12 PM »
That's absolutely the right concept (temperature-variable, used in oscillator circuit, especially in pushbutton-tuned radios) and the right era (3 years before my radio was sold)  but completely the wrong shape.  The device in my radio is bullet-shaped.  Aargh.  It would have been so nice of they had suggested a value.

Chris Campbell