What the heck is bias anyway?

Hey Stanwal, transistors have to be biased too... and for the same reasons.

If you overbias the tube (set it so that there is too much current flowing) the tube will run hotter and distortion is sometimes higher. This would be particularly true of any class A amplifier.

In a class AB amp, if the bias is set to high you can roast the tubes. Its a good idea to set it correctly according to the specs or procedure.

Lesse... the setting of the bias has *no effect* on the power output. It affects the distortion and the heat of the tube (or transistor).

I think if the signal current(music) exceeds the bias current, then there is no sound or just tons of distortion.

Once properly set, if the audio signal exceeds the bias value there are no worries. That's kind of the point of being able to amplify.

Distortion pedals used for guitars use a variety of techniques to make distortion and that is a subject for a different thread.

Mitch4t, this depends on the amp. Some amplifiers have very stable bias settings and can be checked maybe once every 6 months. Others seem to need constant observation. So I would go with the manufacturer's recommendations.

Mitch4t, automatic bias as a feature varies from amp to amp. With some systems it is quite simple and others rather complex. The accuracy varies too. For the most part what autobias means is that the most 'fiddling around' will have to do with initially setting up the amp, and after that dealing with the occasional bad tube. None of that is particularly difficult. You can run into issues with any audio product that might be equally as easy or perplexing.