tube amplifier auto bias- accurate?

I am sorry to disagree with everyone so far. I have owned numerous tube amps from low cost to very expensive. Some auto biasing and others not. There is NO substitute for having your amp biased by a professional with a scope. None.
Ask a tech and see if they don't concur.

Does manual biasing always drift over time? So the amp is always slightly off without auto-biasing. So this could be very tube depended. Some output tubes can last quite a while without drifting while other change on a weekly or monthly basis.

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?