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From: Cursitor Doom <cd999666@notformail.com>
Newsgroups: sci.electronics.design,sci.electronics.repair
Subject: Re: Oscillator Distortion
Date: Sun, 13 Oct 2024 17:12:31 -0000 (UTC)
Organization: A noiseless patient Spider
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On Sun, 13 Oct 2024 17:10:30 -0000 (UTC), Cursitor Doom wrote:

> Gentlemen,
> 
> Last week I got an old (1968) pulse generator out of mothballs and
> managed to get it fully functional again. However, before replacing the
> case, I (true to form) dropped it on the bench and something on the PCB
> must have shorted out against the metal tools it fell on, because it no
> longer works properly.
> I've found an issue with the principal oscillator. It's generating
> distorted sine waves. It's a wien bridge type using BJTs as the gain
> element and fine tungsten filaments as thermistors, so should produce
> near perfect sine waves before they're chopped and shaped by subsequent
> circuitry, but since the fall, it's not.
> 
> Here's the oscillator output:
> https://disk.yandex.com/i/eKAe95xMsiIvNA
> 
> I found some weird periodic spikes on the power supply rails in the
> oscillator stage. They are actually present on the rail, not just picked
> up by the ground lead of the scope out of the ether, as I used a short
> ground clip in this instance. I'm not sure if these could cause the
> distortion or not.
> [removed]
> 
> I'm out of ideas. What could cause such distortion if the PS rail isn't
> responsible?
> 
> Your pal,
> 
> CD.

Sorry, the trace of the 'ripple' should have been this link:
https://disk.yandex.com/i/P7AIraCaJybIMw