SFDR Amp Hum

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

  1. May 9, 2005 #1
    coyoteblue

    coyoteblue Member

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    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?
     
    coyoteblue, May 9, 2005
    coyoteblue, May 9, 2005
    #1
  2. May 10, 2005 #2
    Blue Strat

    Blue Strat Member

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    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.
     
    Blue Strat, May 10, 2005
    Blue Strat, May 10, 2005
    #2
  3. May 10, 2005 #3
    Wakarusa

    Wakarusa Member

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    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)
     
    Wakarusa, May 10, 2005
    Wakarusa, May 10, 2005
    #3
  4. May 10, 2005 #4
    johnnyguitar

    johnnyguitar Long in the tooth

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    Can you say filter cap.....????
     
    johnnyguitar, May 10, 2005
    johnnyguitar, May 10, 2005
    #4
  5. May 10, 2005 #5
    coyoteblue

    coyoteblue Member

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    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.
     
    coyoteblue, May 10, 2005
    coyoteblue, May 10, 2005
    #5

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