Laney RB9 Richter Bass Head Biasing

[jondoe]

Hi all,

I recently replaced the all the output transistors on a Laney RB9, while trying to bias the amp I've seen fluctuation when left on for some time. I've biased the amp to 10mv after about 20 minutes turned on from cold and at idle, although the trim pots are very sensitive, I can get it pretty much get it on 10mv, maybe +0.1 at worse. After another hour I'll test again and it will have dropped to 8.5mv, or sometimes moved up to 12mv.

The service manual doesn't state if the amp should be under load or not, just that it should be biased to 10mv. Should I worry about these fluctuations?

Thanks.

[Jon Snell]

The bias is set with no load and no signal. Your measurements look about right.

[jondoe]

Thanks Jon, I'll button it up and call it fixed

[g1]

You may have found that the line voltage was fluctuating also (resulting in idle current change).