Model 66b Warm-up drift - Printable Version

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+--- Thread: Model 66b Warm-up drift (/showthread.php?tid=3311)

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Model 66b Warm-up drift - bob913 - 05-29-2011

Replaced all electrolytic & paper caps along with 6 resistors. Did not replace the bakelite caps. I've noticed that it takes about 15 minutes for the radio to warm up and stop frequency drift. Is this normal for a 1935 radio or could it be attributed to another item, such as bakelite caps? Bob.

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Re: Model 66b Warm-up drift - codefox1 - 05-29-2011

All old sets drift a little bit. I think you probably still have one or more carbon resistors that is high in value, and it gets worse with a little heat. At a nickel or so apiece, why haven't you replaced them all? Wirewounds are either good or bad or shorted to the chassis. It's a crapshoot with mica capacitors, usually you get crackling or loss of signal, but drifting could also occur. Of course there are more bizzare things that could be going on too.

Let's see who else has some tips.

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Re: Model 66b Warm-up drift - exray - 05-29-2011

Hi Bob,

Well, it wouldn't be unusual to note some drift in the first 15 minutes but the question is how much is too much. In relative terms you should be able to turn it on to an AM station and maybe have to touch it up slightly once after warmup. Shortwave would be different.

I can't think think of a scenario where any of the Bakelite caps would cause this unless they were really leaky and pulling down the voltage - and that's not out of the realm of possibility. I'd rebuild them on general principle because there's so many other potential problems that could develop.

If you have another 6A7 handy you might try it. I've caught excessive drift in many radios due to some problem with the LO/Converter tube.

Just my 2 cents.

-Bill

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Re: Model 66b Warm-up drift - bob913 - 05-29-2011

Thanks for the replies. Besides not replacing any of the bakelite caps, I also did not replace any of the dog-bone resistors. Looks like I have some more work to do. Bob

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