XPost: sci.electronics.design   
   From: cd999666@notformail.com   
      
   On Sun, 20 Oct 2024 11:24:06 +0200, albert wrote:   
      
   > In article ,   
   > 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.   
   >>https://disk.yandex.com/i/eKAe95xMsiIvNA   
   >>   
   >>I'm out of ideas. What could cause such distortion if the PS rail isn't   
   >>responsible?   
   >   
   > Not entirely unrelated to this subject.   
   > Image a Wien bridge oscillator, stabilized with a lightbulb. This could   
   > be described with differential equations, including the heating and   
   > cooling of the tungsten wire.   
   >   
   > I suspect a relation between the cooling time constant and the periods   
   > of an oscillator, and the distortion.   
   > A rule could be if you need N periods to have the distance to the the   
   > stable wave halved, you have circa 1/N distortion.   
   >   
   > Is this known territory?   
   >>   
   >>Your pal,   
   >>   
   >>CD.   
   >   
   > Groetjes Albert   
   >>   
   >>   
      
   You people who explain everything they see in terms of higher mathematics   
   normally leave me baffled. But I believe I've deduced what you're trying   
   to say and it's not an issue in this case. Thanks for the suggestion   
   anyway.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)