Vintage Asylum

RE: Your hum is in the signal path because it changes with volume

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PeterI

In Reply to: RE: Your hum is in the signal path because it changes with volume posted by Michael Samra on January 12, 2016 at 11:30:32

Thanks, but there is no CT on the heater windings. I think filament AC has something to do w/ the buzz. But I tried resistors to ground and capacitors on the heater circuit to see if it changed. It didn't.

Yes, installing back in the cabinet helped diminish the buzz a bit.

Follow Ups:

Heater lines - FenderLover 10:53:22 01/13/16 (8)
Does the heater line have resistor at the ends, to make an artificial center tap?

Fender usually uses 100-ohm resistor tied from each heater end to ground. At the power lamp.
- RE: Heater lines - Michael Samra 12:00:03 01/13/16 (7)
  The schematic he posted shows a filament center tap to ground.
  
  Nobody ever went broke underestimating the intelligence of the American public
  H. L. Mencken
  - RE: Heater lines - Crazy Dave 13:43:06 01/13/16 (2)
    Hi Mike,
    
    Would switching to 12AX7LPS tubes help in this situation?
    
    Dave
    - RE: Heater lines - Michael Samra 18:25:43 01/14/16 (1)
      That is a miracle tube so it may help.
      
      Nobody ever went broke underestimating the intelligence of the American public
      H. L. Mencken
      - That sounds like a recommendation to me! (nt) - Crazy Dave 07:15:42 01/15/16 (0)
        
        In Reply to: RE: Heater lines posted by Michael Samra on January 14, 2016 at 18:25:43
  - RE: Heater lines - PeterI 13:38:32 01/13/16 (3)
    There doesn't seem to be a CT for the heater, despite what the schematic shows. I tried adding 200ohm resistors to the heater cables to ground. No effect, so I removed them. I think there is an internal leak in the PT.
    
    Now I wonder about the fact the manufacturer used the unused pins on the 5Y3 rectifier socket as tie points for the heater cables coming out of the PT. Kinda close, causing EMI noise? Probably not, since we have determined the noise is likely in the signal path.
    
    Thanks for suggestions.
    - Input lines - FenderLover 18:32:54 01/13/16 (2)
      Peter, You did try shielded line from input jacks to the input stage? Grounded at jack side, only?
      
      Thanks!
      - RE: Input lines - PeterI 10:46:48 01/14/16 (1)
        
        In Reply to: RE: Input lines posted by FenderLover on January 13, 2016 at 18:32:54
        
        I did but it's a moot point since EVERYTHING is grounded to the chassis, including the input jacks. There's no signal ground. Adding a 3" shielded cable from jacks to the input resistors and then 4" to 1st tube grid had no effect on the unwanted buzz. I expected some result or fix. Guitar amps are odd beasts; crude compared to what I usually work on.
        
        Edits: 01/14/16
        
        RE: Input lines - DannyR 12:31:54 01/14/16 (0)
        
        In Reply to: RE: Input lines posted by PeterI on January 14, 2016 at 10:46:48
        
        okay. are you trying the amp with a guitar with humbuckers? Single coils will pick up some noise. if it buzzes with the guitar unplugged check the input jacks to see if they are wired correctly/shorting.

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