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RE: Unusual problem - puzzle

Posted by fredtr (A) on August 24, 2020 at 12:31:31

In Reply to: RE: Unusual problem - puzzle posted by airtime on August 23, 2020 at 18:59:33:

Airtime, you're right that critters were involved. The original problem was a cold solder joint on a filament connection of the first tube in the amp. The volume would fade as the filament went out, and build as it again made connection and warmed. It was original wiring, I was tempted to see if Quad has lifetime workmanship warranty. The amps were made in the 50's or early 60's.

The interesting part was why I could hear music from some speakers and not others when I turned the balance so only the bad channel was on. It turned out that thanks to the critters, one channel path on one main branch of speakers was 90 ohms. The increase in impedance, allowed the crosstalk across the non lit tube and adjacent circuity to be audible. It was also interesting that the increased resistance was not causing audible problems under normal conditions. The separation and volume sounded ok, and this was with speakers that were quite far apart. I stood equal distance and the balance seemed fine.

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