SFDR Amp Hum

coyoteblue

Silver Supporting Member
Messages
242
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?
 

Blue Strat

Member
Messages
30,194
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.
 

Wakarusa

Member
Messages
1,458
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)
 

coyoteblue

Silver Supporting Member
Messages
242
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.
 




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