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Gibson Super Goldtone GA-60RV


JohnGer

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Hello,

I am looking for help on how to bias the tubes of a Gibson Super Goldtone GA-60RV.

It is running EL34s. The manual has instructions but they are unclear and I have never biased tubes before.

The amp has bias test points at the back of the amp with bias adjustment pots between them in this configuration: V2 test point - adjustment pot - 0V test point - adjustment pot - V1 test point

To bias the tubes it says use a voltmeter and place the black probe in 0V and the red probe in V1. Adjust the pot to show 33mV. Then it says put the black probe into V2 and adjust the pot to read 0mV.

Can anyone tell me, am I supposed to leave the red probe in V1 when I do the second adjustment? Does this sound right?

Someone else told me to leave the black probe in 0V and adjust each side to read 33mV. Which is correct or can it be done either way?

If anyone could clarify how to do this, I would appreciate it. I don't want to cook my amp or tubes.

Thanks!

John

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I think you can do it either way. Either keep the red probe in the 0V test probe and use the knob for each side to adjust each side independently to 33mv or, like they say in the manual, adjust one side to 33mv and then take the black probe and stick it in the other hole and adjust between the two sides, which should be close to 0v. BTW, there's negative voltage in that circuit and that's why you put the red probe in the 0V hole. So it will read + volts and then you can use an analog meter with a needle. You can swap the red and black leads and your meter will read negative voltage with the black probe in the 0V hole.

 

Nice amp!! [thumbup] [thumbup]

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BadBlues,

Thanks for the input. I just thought of the idea of doing one method, then measure with the other method to see if I get the correct readings for that second method. I figure if one is dialed in then the other should be too if they are both acceptable methods. I have no idea if that is correct but it makes sense to me.

I really like the amp, I play alternative and pop styles. I really like both the clean and distortion channels.

Thanks again.

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I tried what I described and it appears to have worked. I set the voltage as you described and then checked to see if it was 0 mV as in the second step according to the manual and it was at 0. So I assume they are two different methods that arrive at the same end result. Thanks again for your help bad blues.

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