From: cd999666@notformail.com   
      
   On Mon, 14 Oct 2024 11:41:24 +0100, Liz Tuddenham wrote:   
      
   > Cursitor Doom  wrote:   
   >   
   >> On Sun, 13 Oct 2024 17:39:53 -0700, Dave Platt wrote:   
   >>   
   >> > In article ,   
   >> > Cursitor Doom   wrote:   
   >> >   
   >> >>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.   
   >> >   
   >> > Is there a chance that the impact broke one of those fine tungsten   
   >> > filaments?  Do they read low-Z when cold, as they should?   
   >>   
   >> It's one thing I need to look at, if only for the sake of completeness,   
   >> next time I have access to it. Since these are so hard to replace, I'd   
   >> really rather deal with my original suspicion that something got   
   >> shorted out in the fall.   
   >   
   > Could a pre-set pot have gone open circuit?   
      
   I don't think so. TH2 on the schematic appears to have gone open circuit.   
   Those filaments are pretty fragile! Not sure what they've used - looks   
   like one of those old dashboard bulbs you see in old cars. I won't be able   
   to find a direct replacement, but I do have some spare thermistors from   
   other wein-bridge test gear I've plundered over the years which I dare say   
   could be pressed into service with a little teak of the biasing. I might   
   even experiment with some small filament bulbs which are not part of the   
   WB variety just out of curiosity.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)