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Topic: Fender amp question |
Steve Spitz
From:
New Orleans, LA, USA
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Posted 18 Mar 2012 12:54 pm |
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My 1995 Fender Custom Vibrosonic Reverb has two adjustable pots on the underside of the chassis. One is closer to the side of the cabinet , the other closer to the middle of the cabinet. Can anyone tell me which one does what, (I'm guessing one is bias, relating to running"hot or cold)" and the other ?
Are either of these user friendly to be used to adjust "by ear " or should I only leave it to a qualified tech? I have an ohm meter, but I'm not qualified to work on high voltage gear.
Thanks. |
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Al Carey
From:
Dublin, NH USA
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Posted 18 Mar 2012 3:57 pm
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| Most likely they're pots for adjusting the bias of each output tube individually. Biasing a tube amp is not particularly difficult, but if you're not comfortable with the idea, don't attempt it. Voltages inside a tube amp are lethal! |
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Steve Spitz
From:
New Orleans, LA, USA
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Posted 18 Mar 2012 4:13 pm Biasing
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| Thanks Al, your words of caution are appreciated. If the pots balance individual power tubes, with four tubes wouldn't I have four pots? I marked where the pots were set, and fiddled with them a bit. One seemed to have an effect on hum, the other on the amount of clean vs grit. Not a very tech savy report, but that's what it sounded like. After my tinkering, I found it to sound best left as I found it. It would be nice to know exactly what each pot was for. I believe each channell uses two power tubes, 1 the two outer tubes, 2 the two middle tubes. Looking at the circuitry, the pots appear to have very different functions. |
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Al Carey
From:
Dublin, NH USA
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Ken Fox
From:
Nashville GA USA
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Posted 18 Mar 2012 4:30 pm
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| One is the heater hum balance and the other is the bias pot |
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Steve Spitz
From:
New Orleans, LA, USA
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Posted 19 Mar 2012 5:19 am Amp
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| Thanks! |
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