What is bias a tube amp ? Is it difficult?

I don't understand auto biasing vs manual biasing? Why wouldn't all tubes be auto/self biasing? What is it about the nature of an amp, or the manufacturer, or whatever, that one would produce an amp without this feature? thanks in advance, warren :)

Warren,

My amp designer states that auto-biasing impacts the sound of an amp, and not positively. Nick makes the best sounding electronics I've been privileged to hear, regardless of price, so I believe him. In top level gear manual biasing is probably preferable.

Aside from any degradation caused by unneeded complexities in the circuit, our own ears tend to confirm this from another direction. We readily hear any small changes we make in bias levels, so if the amp were constantly monitoring and adjusting...

Biasing and balancing four power tubes once every 6-8 weeks takes all of 10 minutes. It's no big deal, as others have said. YMMV of course.

Well made amps don't require biasing very often, and it's a good idea not to go crazy with this simply because frequent biasing will prematurely wear out the pots.

The CJ and Rogue amps I have are basically set it and forget it. I check the bias once every six months or so on the Cronus but with the CJ I haven't had to touch the bias for almost year now. And I am running Winged C Svetlana EL34s in each.

Stevecham,

Now that you mention it, I haven't actually *changed* the bias on my amp since I nudged a new quad of Sovtek Reflektors up to full operating level. That was last May or June, and they're running at the same level today and presumably for the forseeable...

I check it out of habit every month or two but, as you say, a well-designed circuit that doesn't overdrive the tubes should remain stable for long periods.

Great. Another thing NOT to worry about. I hate that!

The Rogue M-150's I'm using hold bias very well. As others have mentioned biasing is really easy and not something that needs to be done very often. As I understand it, having a way to bias the tubes in the system can save you money in not necessarily needing to purchase well matched sets. I also like the option of running some tubes a bit warmer or cooler to tweak the sound.