Tubes Asylum

• Re: Flaw in Design? - Jim McShane 06:08:59 08/23/04 (3)
  In Reply to: Flaw in Design? posted by Will C on August 23, 2004 at 04:54:21:

  What's the voltage at the tube's cathode? The voltage across the tube is the difference between the plate voltage and the cathode voltage. So if the cathode is at 90 volts or something, then the tube is only seeing 300 - 90, or 210 volts. 210 volts or thereabouts is just fine for a 6922.

  Back when I was learning basic electronics, I got more help by remembering that voltage = potential difference than any other little "trick".

  So the plate voltage may be 300 volts above ground, but what's the "potential difference" across the tube?

  I don't know the circuit you describe, but I'll bet you a beer that there's significant voltage on the tube cathodes.
  
  

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  • Re: Flaw in Design? - Will C 06:52:24 08/23/04 (2)
    In Reply to: Re: Flaw in Design? posted by Jim McShane on August 23, 2004 at 06:08:59:

    Thanks very much Jim.

    I measure 142 volts at the cathode. That would certainly be within limits. 290 volts - 142 volts.
    I could email a so-so scan of the schematic if anyone is interested.

    Bill
    
    

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    • Re: Flaw in Design? - Victor Khomenko 06:56:40 08/23/04 (1)
      In Reply to: Re: Flaw in Design? posted by Will C on August 23, 2004 at 06:52:24:

      Connect the voltmeter to cathode and plate of that tube, let the amp sit in OFF state for a few hours and then turn it on.

      Some tube circuit might have strange turn on behavior, voltages swing widely before tubes stabilize...

      Simply because you seemed curious about what the amp is doing.
      

      
      
      
      

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      • Re: Flaw in Design? - Will C 07:07:34 08/23/04 (0)
        In Reply to: Re: Flaw in Design? posted by Victor Khomenko on August 23, 2004 at 06:56:40:

        Thanks Victor.
        I'll certainly do that!

        Bill
        
        

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