SFDR Amp Hum

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by coyoteblue, May 9, 2005.


  1. coyoteblue

    coyoteblue Member

    Messages:
    230
    Joined:
    Feb 26, 2005
    Location:
    Peterborough, ON
    I recently bought a 77 SFDR and had it fully serviced. When I bought it it had a fairly loud hum and after it was serviced it still has a fairly loud hum. Loud enough that I can hear it across a room. Two techs have said there's nothing that can be done about it unless I start replacing the wiring itself. On the other hand I've read in various places on the net that pretty much any amp can be made quiet. So, are some amps just more likely to have a louder hum than others, even in the same model, or should I go find a third tech?
     
  2. Blue Strat

    Blue Strat Member

    Messages:
    29,953
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    You might possibly need another tech. It shouldn't be so loud that you hear it across the room.

    Have you tried swapping tubes? Start by removing the PI tube (V6) and see if this improves things. If so, the problem is in the preamp or PI...if not, the problem is either the power tubes or power supply.
     
  3. Wakarusa

    Wakarusa Member

    Messages:
    1,477
    Joined:
    May 7, 2004
    Location:
    Newnan, GA
    Also, if it isn't a tube, there's always the chance that one of the fresh filter caps didn't live up to the manufacturer's service life claims.

    (typing this as I take a break from re-replacing a filter cap that went south in a SFDR after a scant three months)
     
  4. johnnyguitar

    johnnyguitar Long in the tooth Silver Supporting Member

    Messages:
    731
    Joined:
    Jan 4, 2002
    Location:
    Golden Colo
    Can you say filter cap.....????
     
  5. coyoteblue

    coyoteblue Member

    Messages:
    230
    Joined:
    Feb 26, 2005
    Location:
    Peterborough, ON
    I'll check out the caps, though I doubt that's the cause because the hum was there before and after replacing the old filter caps with new ones, top of the line Mallorys. Thanks for the suggestion.
     

Share This Page