Posted by Russ57 (A) on April 26, 2007 at 11:06:08

In Reply to: clarification posted by rude52 on April 26, 2007 at 10:03:08:

We can make an educated guess as to what job it does and possible reasons for failure. Sometimes parts are speced on the edge and it helps to go up a step in voltage and/or temperature rating. I'm inclined to think it might be a bypass cap for the 300B bias resistor. If so I'd look at voltage and temperature rating.

Russ

• IIRC 100uF and 100V (nt) - rude52 14:30:14 04/26/07 (3)
  In Reply to: If you tell us how many uF and what voltage posted by Russ57 on April 26, 2007 at 11:06:08:

  nt
  
  

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  • Just as I thought - Russ57 04:59:45 04/27/07 (2)
    In Reply to: IIRC 100uF and 100V (nt) posted by rude52 on April 26, 2007 at 14:30:14:

    I'd certainly up the voltage rating to at least 160VDC. Also go for a 105C temp rating. There should be a resistor near by, a large high wattage one. Check that and see if it is still the proper value. I'd use a 12 watt mills. Black gate would be nice for the cap. Neither are cheap but those parts are quite important to the sound of the amp.

    Oh, don't forget to have your tubes tested. We don't know what failed first. And yes a bulging cap is a bad one.

    Russ
    
    

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    • Re: Just as I thought - Paul Joppa 11:38:14 04/27/07 (0)
      In Reply to: Just as I thought posted by Russ57 on April 27, 2007 at 04:59:45:

      Also check for leakage of the coupling capacitor, and a good grid resistor. If the grid bias drifts up from the above or a gassy tube or whatever, it will raise the cathdoe voltage, possibly driving the cap to over-voltage. Heat and voltage are the cap-killers.
      
      

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    • thanks all - rude52 09:57:13 04/27/07 (0)
      In Reply to: Just as I thought posted by Russ57 on April 27, 2007 at 04:59:45:

      Hi Russ and everyone,

      Thanks for the advice. I will check out the specs and the tubes.

      As for the blown caps, a quick web search showed me more than I would ever want to know about elctrolytic cap failure in motherboards! I should have realized that the design on the bottom of lytics is a vent.

      Cheers

      Rich
      
      

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