tube amplifier auto bias- accurate?

I am a bit confused by the terminology. When I was involved with tube power amps there were three schemes which went like this.

"self biased" ....Bias voltage derived by a fixed resistor from the plate voltage. No provision for any adjustment. Output power reduced by about 10 percent compared with adjustable.

"adjustable bias"....Bias provided by a separate voltage generated by the power supply, and having adjustment capability by a pot.

"AutoBias"....Same as adjustable except with the pot replaced by a circuit that makes measurements and adjusts voltage accordingly.

Bin, yes there is a substitute. I'm using one!

BIN,
ofcourse a tech is going to concur. How would he get paid otherwise?

"adjustable bias" - this is actually called Fixed Bias (yeah, great naming convention, I know).

within the realm of 'auto bias' there are many possible ways to do that concept. Same with fixed bias - eg. separate bias power supply, winding, or tranny, various rectification schemes for bias supply, battery-biasing, etc.

bin:
biased with a scope? What the hell are you talking about? Bias is a voltage, nothing more or less. A good voltmeter is all that is needed. it's either accurate or its' not. There's nothing to graph on a meter. Tech's must have been having a laugh at your expense, methinks.

-Ed

While autobias is certainly more convenient, and I do not know if one is better than the other sonically, I have heard manufacturers claim that adjustable bias normally yields longer tube life.

In fact, Rogue's new amplifiers have made the switch from autobias to user adjusted bias. In addition to the tube life, I have read they feel it also has produced better sonics.

If sonics were equal, obviously autobias is preferable. If there is some audible improvement by not implementing the circuit, it would be good to go in that direction, and make bias adjustment an easy task, with easy accessibility to the adjustment (like AtmaSphere, Cary, CJ, Jolida, Quicksilver, but NOT like Jadis).