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.

rwe62
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Re: Peavey Classic 60/60 Bias Mod

Post by rwe62 » Tue Nov 09, 2021 2:56 pm

Enzo, I used your Enzo-Campagnola mod for a 60/60 and it was brilliant. I have a 120/120 that I would like to get a better tone. Do you have a mod or suggestions for this powerhouse? Thx

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Enzo
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Re: Peavey Classic 60/60 Bias Mod

Post by Enzo » Tue Nov 09, 2021 8:40 pm

All I can tell you is you can make the bias adjustable just like the 60-60. The 470 ohm and 47k ohm resistors in the bias supplies need to be changed in the exact same way. 470 ohms is just way too low for voltage division. Note the stereo mono switch switches all output tubes to one bias supply.

I don't really mess with these much as they are designed to be strong and loud and clean. I can't imagine the average soul intends to try and overdrive the power amp.

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