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Old 05-20-2016, 01:18 AM
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Electronic M Electronic M is offline
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Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
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Quote:
Originally Posted by radiotvnut View Post
Here's a crude schematic I drew. It's odd that the tone controls are in the cathode circuit of the 12AX7 and one of the leads from the extra winding on the transformer goes back to the tone control. If this was a handwired amp, it would be much easier to modify it. However, since it's a PC board, it's going to be harder to deal with. Leave it to Sears to come up with some goofy circuit design.

I'd look at the good half of the amp. Is the amplitude of the feedback winding is the same or lower than the speaker winding? Is there significant DC voltage across the feedback winding? If both answers are yes, then just use a single secondary spare and use the one secondary to drive feedback and speaker at once. If only the second is no, then use a large capacitance value to couple the voice coil winding to the feedback circuit so you are not sending tons of DC through the speaker. If it works decently on one channel you may want to do it for both so there is not a tonal mismatch between channels.
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