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Tube amps

11/5/1999 9:11 PM
Mike O
Tube amps
Is there a certain amount of noise associated with tube amps? I just had some work done on an old Fender ampthat I've had for about 30 years. The amp has good sound but stil has a slight continuous buzzing not real loud but audible.Is this normal or should I call the tech and ? it.I won't metion his name but, he is probably the best in my area  
Mike O
11/5/1999 9:15 PM

Some buzz and hiss is normal. Some are worse than others.  
Lead dress helps, but won't always solve the hiss/buzz problem.  
Other items that are suspect are microphonic/noisey tubes, resistors, scratchy pots, leakey caps, etc.  
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11/5/1999 9:44 PM
Mike O

All of the things you mention were checked out.  
Some plate resistors were replaced,pots cleaned  
tube sockets cleaned and the bias was set.Maybe  
I'm expecting to much for an amp that cost me 250  
bucks over 30 years ago and are fetching 700 to 1400  
dollars today. Thanks for your comments.  
Mike O
11/5/1999 10:16 PM
Benjamin Fargen

Is this amp a silverface Fender? If it has the bias balance pot instead of the standard neg. voltage bias will be hard pressed to ever get rid of the hum from the power tubes until you convert it back to blackface specs..........the way Leo Fender designed it!  
Bruce C. has a cool way of coverting it to get the best of both worlds.......bias adjust and hum balance!  
11/5/1999 10:32 PM
Mike O

Yes the amp is a SFSR with an AB763 chassis.this amp  
was in the very early stages of the SF era and I've  
been told there is not much difference if any.
11/5/1999 10:35 PM

OK I'll bite.  
Have you got a diagram of this set up? A description would be OK too. I've got one of those tapped balance pots that I'd like to do that to, or I'll just set up two separate bias pots. I haven't decided, yet  
Bruce C. has a cool way of coverting it to get the  
best of both worlds.......bias adjust and hum  
11/5/1999 11:02 PM
Benjamin Fargen

Here is a link to some great info on blackface vs. silverface Fenders courtesy of Andy at Machine gun amps.  
Read all this documentation and then look at any comparable blackface fender amp schematic to convert the neg. bias supply.  
Bruce will have to jump in and refresh us on his mod.....can't quite remember the specifics.  
This should get you started.  
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