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Wiring Oddity in 37-10 - Printable Version

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Wiring Oddity in 37-10 - Guest - 06-20-2009

Long time reader, first time poster!

I have a 37-10, code 121, and have been gradually recapping and otherwise rehabbing it. At this point the only paper caps that haven't been replaced are a couple still buried in the RF section. There is one period modification, a radio/phono switch and jack wired to the high end of the volume control and installed on the rear apron.

When I got the set, there were oddities with the volume control -- it wouldn't completely silence a strong signal when turned completely down, nor would the audio shorting switch on the automatic tuning wheel. But audio in general was strong and clear, with little distortion.

While rebuilding bakelite block number 41, I noted that resistor 44 was attached to lug number 3, but according to the parts diagram for this set, as seen in Rider's Vol. 8, that resistor should be attached to lug 2. I moved the connection to lug 2, and tried the set. The volume control and audio shorting switch then worked normally. But overall volume is much weaker and thinner -- audio had been rich and room-filling before with the volume control set at about one-half, as I'd imagine it should be with this set, but now it has to be turned up to about 4/5ths to produce a decent listening volume, and the audio quality, especially in the bass, is noticeably weaker.

All of the paper caps in this circuit have been replaced, but the micas and the resistors are original. I tried a new 6Q7 tube, but it didn't make any difference. Voltages appear normal. All resistors in the circuit check out within spec, which leaves only the 110mmfd mica cap across the diode section of the 6Q7. But before I try replacing that cap, I'm wondering what else might be wrong? I believe the other connections on the block are correct, but if one was wrong others might be as well. Anyone have a pic showing clearly how this block should be connected? Am I dealing with a production-run change? A previous repair person's workaround? Something to do with the phono jack modification? Or should I be looking somewhere else entirely for the problem?

Is it safe to operate the set with resistor 44 as I found it? Will this connection pull too much current and cause damage that I'd prefer not to have to deal with, considering how inaccessible many components in the RF section are?

Any advice or suggestions welcome. Thanks!

Elizabeth

Re: Wiring Oddity in 37-10 - exray - 06-20-2009

I'm sort of hesitant to jump into to this Icon_smile

The schematic is a hair puller trying to figure out the 6K5/6Q7 'option'.

http://www.nostalgiaair.org/PagesByModel/196/M0013196.pdf

If it were me I would put it back as the schematic shows and get the external connection out of the equation for the moment...use whichever version is yours. Its impossible to say what they may have done "under the lugs" of the block caps but again, if it were me, I'd tend to start from scratch and follow the diagram and the 'official' block details. If the blocks haven't been recapped already thats justification enough to dive in. The 110pf cap CAN really mess up the audio although I doubt thats at issue here.

Re: Wiring Oddity in 37-10 - Guest - 06-21-2009

I'm thinking about trying that, although more and more I'm thinking this isn't a problem in the audio section of the set -- for one thing, when I feed a signal from an FM tuner via the phono jack it's extremely clean and loud with no distortion. That suggests to me something gone wrong from the 6Q7 diode section back.

I've returned resistor 44 to its proper lug though, and am figuring I'll try that mica cap next -- it's one of those Micamold jobs that can't be trusted.