Peavey Classic 60/60 Bias Mod

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Lord John Worfin
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Peavey Classic 60/60 Bias Mod

Post by Lord John Worfin » Fri Jul 16, 2021 3:02 am

Hi there,

since today I'm owner of a Peavey Classic 60/60. I'm asking myself how to handle the not adjustable, fixed Bias. Does anyone hear about a Bias-Mod for this Amp an can provide any schematics? That would be very welcome.

Best greetings from Berlin

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Enzo
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Re: Peavey Classic 60/60 Bias Mod

Post by Enzo » Fri Jul 16, 2021 11:53 am

I have actully done it, but t isn't simple. The amp has two independent power amps. If you want the bias supply adjustable, that isn't so hard, but if you want to adjust the two channels separately, you will have to duplicate the bias supply circuit. Also othere will be traces needing to be cut and extra wires run.

To make the bias overall adjustable, I'd increase the 470 ohm resistor in the supply to something like 3000 ohms, then turn the 47k resistor into something like a 27k resistor with a 25k pot in series. Pot wired as a variable resistance.

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Lord John Worfin
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Re: Peavey Classic 60/60 Bias Mod

Post by Lord John Worfin » Tue Jul 20, 2021 8:48 am

Enzo wrote:
Fri Jul 16, 2021 11:53 am
I have actully done it, but t isn't simple. The amp has two independent power amps. If you want the bias supply adjustable, that isn't so hard, but if you want to adjust the two channels separately, you will have to duplicate the bias supply circuit. Also othere will be traces needing to be cut and extra wires run.

To make the bias overall adjustable, I'd increase the 470 ohm resistor in the supply to something like 3000 ohms, then turn the 47k resistor into something like a 27k resistor with a 25k pot in series. Pot wired as a variable resistance.
Thanks Enzo, I'll give this a try.

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