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Vintage threads from the first ten years
Bias help!
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 2/29/2004 2:17 AM |
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Bruce J |
Bias help! OK, I am working on a 1964 Super Reverb for a customer and here is the problem. I did a cap job, ie filter, bias and cathode bypass caps. I am trying to bias the S.O.B. but I can't get the bias current to stay put. What I mean is, I set the bias and watch it slowly climb and it won't stop even after 30 minutes of playing the amp. With the plate voltage at 460 VDC I set the current around 45ma to get about 21 watts at idle for starters. So I grab my guitar, the amp sounds good. After a while I re-check the bias and it has gone up to over 60ma. So, I re-adjust to 45ma and watch it. IT just won't stay put! It just keeps slowly climbing and it is pissing me off! What is wrong here? Thanks, Bruce J. |
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| 3/1/2004 2:16 AM |
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| Bruce J |
It turns out that my bias probe is crap. I used the shunt method and got it! |
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