Tubes Asylum

• Re: Do I put that resistor in the circuit to ground? Did you mean 7591's? - Tom Bavis 11:25:29 03/13/07 (2)
  In Reply to: Do I put that resistor in the circuit to ground? Did you mean 7591's? posted by PeterI on March 13, 2007 at 10:32:22:

  Yes, I meant 7591s... there are three preamp tubes that get heater current from the 7591 cathode current. There's a 600 Ohm resistor to ground from there, according to schematic - the 240 Ohm goes in parallel with that, cathode to ground. 244 in parallel with 600 is 171.5 Ohms, 33V across that is 192 Ohms, or 48 mA per tube. I'd also add a 10 Ohm resistor in series with EACH cathode to give a point to check current per tube. Would be nice if the original 7591s are still matched, but I'd check.
  
  

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  • Thanks again. - PeterI 14:35:24 03/13/07 (1)
    In Reply to: Re: Do I put that resistor in the circuit to ground? Did you mean 7591's? posted by Tom Bavis on March 13, 2007 at 11:25:29:

    Thanks.
    I will put in the 240 ohm resistor.
    My Triplett tube tester won't test these 4 nice Sylania 7591s - they're too 'modern'. I wish my Eico 667 tester wasn't acting up but I can't trust the readings. That's a good tester.

    Pete

    Vintage Voltage Expo - Denver, March 25
    
    

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    • Any suggestions about upgrading this amp welcome (nt) - PeterI 21:05:41 03/13/07 (0)
      In Reply to: Thanks again. posted by PeterI on March 13, 2007 at 14:35:24:

      nt
      
      

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