Resistor variances (John Phillips please read)

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by d l x r e v e r b, Mar 7, 2008.

  1. d l x r e v e r b

    d l x r e v e r b Member

    Messages:
    344
    Joined:
    Jan 12, 2006
    Hello ,

    A thread a few weeks ago asked about changing resistors if they were beyond the part's stated variance. For instance "how far out of spec is too much of a variance ?"

    John Phillips mentioned the resistors on the power tubes should be replaced if anywhere beyond the stated variance while the other resistors are less crucial and could be as much as 50 percent out of spec before needing replacing.

    Question : On the Fender Deluxe Reverb AB763 schematic the only resistors with a close variance of 5 percent (gold stripe) are in the Phase Inverter section. Should these resistors be as vigilantly checked as the resistors on the power tubes ? I assume if Fender felt the need to use a 5 percent variance rather than usual 10 percent variance the application would benefit from resistors as close as possible to the specified value and not be allowed to drift very far.

    Thanks
     
  2. 5E3

    5E3 Member

    Messages:
    5,068
    Joined:
    Feb 26, 2008
    Location:
    Denver, CO
    Last I heard John Phillips was on hiatus from TGP. I don't think he is back yet :(
     
  3. pfflam

    pfflam Silver Supporting Member

    Messages:
    7,060
    Joined:
    Aug 26, 2005
    Location:
    PDX: The Rose City
    Boy . . .I hope that won't last, he is so helpful and has been so generous.
     
  4. rockon1

    rockon1 Member

    Messages:
    11,493
    Joined:
    Aug 12, 2005
    Location:
    Stamford CT

    Sadly it is true. Bob
     
  5. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    My policy on resistor replacement, beyond the power tube sockets, is to let your ear be the judge. Some amps of the same type sound magical, others not. If the magic is due to drifted resistors then so be it.

    In general, I think resistors that are out by more than 20% should be considered candidates for replacement. Try a closer value and check the affect on the tone of the amp.

    There's no absolute answer beyond this.
     

Share This Page