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I suspect sometimes the buzz problem was audio IF tuning related. I've got a 71 hybrid set with the buzz tube. The thing regardless of the buzz control setting or modulator used has some buzz on all channels even when other Zenith's with the same tube won't buzz....A few years ago I got my hands on a vacuum tube video only RF modulator, and proceeded to add a tube FM modulator to it (generates a 4.5MHz FM carrier that I mix with the video signal at the AM video modulator) I found that modulator worked normally on all sets when set to 4.5MHz, and still buzzed on the Zenith.... Until, on a whim, I de-tuned the sound carrier in the modulator for best audio in that Zenith and the buzz stopped....I suspect if I did a proper sound alignment I could kill the buzz. I haven't gotten around to proving that hypothesis yet.
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