Manual vs. Auto Bias

Anjowin,
I have a push-pull 100 watt amp(6550/KT88 tubes) that requires manual biasing(very simple to preform) that sounds very good. I also own an auto biasing 300b SET amp that`s the best sounding amp(without question) i`ve ever owned thus far.If a auto bias circuit (in theory) adds distortion, that has`nt been my experience at all.

I have one "auto bias" amp, a Cary SLI 50 and I think it sounds great. My other amp is a VAC PA100 which is a manual bias via LED's on the frt panel. It is very easy to bias. Which type of bias circuit is used is not a make or break deal for me. However, amps requiring manual bias that require removing panels and covers, which would be difficult and or dangerous to bias, are off my ownership list. Some amps in this category are models from ARC and Jadis.

Autobias has a main advantage over fixed bias that tube life is much longer than in fixed bias. During powering up an auto-bias self-adjusts the quiescent current thus giving a tube a 'soft' start.
Sonically It's also more beneficial since stabilization of quiescent current decreases distortion.

Marakanetz,
Thanks for bringing up that point. The builder of my Coincident amp as I recall did mention soft startup for the tubes in this design, and said tube life is very long.

More over I'd say that if I ever go back to tubes, I'll make sure I'll buy an auto-bias amp or if price is convincably low for fixed-bias unit, I'll DIY implement it(most-likely with SS parts for less space and money).