Tubes Asylum

• RE: D70 Output Tubes Drifting WHILE Biasing - Lee of Omaha 09:31:25 03/25/14 (1)
  In Reply to: RE: D70 Output Tubes Drifting WHILE Biasing posted by Jonesy on March 24, 2014 at 18:15:35

  I like the hypotheses about the coupling caps and the bias pots. If they turn more easily you definitely got some in there. AND you saw some improvement. Try cleaning again. If that doesn't work try replacing one or more of them.
  
  We had a preamp in once that I cleaned the hell out of the balance pot, and it would play properly for a while, then get noisy. To make a long story short, after about 5 cycles of cleaning/working/noise I replaced the damn pot. That fixed it. Learned my lesson--not everything will clean.
  
  Lee
  

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  • RE: D70 Output Tubes Drifting WHILE Biasing - Jonesy 10:23:26 03/25/14 (0)
    In Reply to: RE: D70 Output Tubes Drifting WHILE Biasing posted by Lee of Omaha on March 25, 2014 at 09:31:25

    Thanks Lee.
    
    Last night I was flipping through the Mouser catalogue looking at pots and capacitors, though it looks like I may have to get the "boutique" type capacitors elsewhere.
    
    I will keep testing, cleaning and checking for solder joints that may have gone bad. Wish I had better test equipment than a multi-purpose DVM. Be nice to have one that checks capacitors though. I guess I can at least check them for shorts/resistance.
    
    Cheers!
    
    Jonesy
    
    "I know just enough to get into trouble. But not enough to get out of it."
    
    

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