Manual vs. Auto Bias

I thought "fixed bias" meant you could NOT adjust the bias...no pot available in the design for that. I think most tube amps allow for bias adjustment, and auto bias merely does it for you on the fly...and that's good.

Kevin Hayes at VAC does not like any of the auto bias circuits out there. He says sound is compromised somewhat and that is why he does not have it.

I still say buy it for sound, unless there's a reason for not doing it yourself. Some may be to hard to do, but check out if you could do manual bias first on an amp you may like. After having at least 20- 30 or more in my system, I have heard great both ways. And that number I gave can be low. Over the years, 4-6 of us bought and swapped amps.

You don't need a Fluke True RMS meter for this task. I have a couple of Fluke True RMS meters, and you could use a regular good digital multimeter to do it. The True RMS is for measuring AC only or a EE, Designer, Tech or other to check its output. Not something for the average person to do. And most don't have or need the other equipment to do that.

I suspect that excellent sound can be achieved with either auto or manual bias, given the superb tube amps available in both categories.Certainly auto bias has`nt been detrimental as implemented in my 300b SET amplifier.

My bad. I ASSuMEd auto-bias meant auto-adjusted by the amp itself, fixed-biased meant there was no adjustment knob/screw to change the bias, and manual-bias meant the adjustment could be made manually by adjusting a control knob/screw.