What the heck is bias anyway?

I dunno Trelja, I'm going to have to stick by it. Amplifiers and and cars are certainly different, but the main, general pragmatic, neophyte-level points between bias adjustment and idle throttle angle correlate well:
- They both determine the level of energy dissipated by the system while it's performing no work, but in an active state waiting to be used
- The proper setting is one that is neither too high nor too low, depending on the machine's design and intended application
- A misadjustment of either rarely results in a catastrophic condition, but results in reduced performance and/or increased stress on the system
- Both are traditionally adjusted by turning a little doo-hickey with a screwdriver, in a manner hidden from the casual end-user
- A similar level of mechanical/electrical aptitude and tools are required to adjust either to a factory-specified setting
- Deviation from the "stock" setting is ill-advised, unless you have the technical competence to evaluate the many interrelated system parameters

Above all, I think this analogy gives a good insight to one who is unfamiliar, whether it's something he/she should be comfortable twiddling with.

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.

Kirkus, where the analogy of idle speed falls apart is with an engine, regardless of whether I set the idle speed at 500 (for the sake of example - too low), 800 (recommended), or 1650 (too high) RPM, performance will be identical at 2500, 3500, or 6000 RPM.

With a tube amplifier biased at 20 mA (again, for the sake of example - too low), 50 mA (recommended), or 75 mA (too high), its performance will be different in readily apparent ways when playing music.

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How often to you have to set and check the bias on a tube amp?
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My injectors are class D but I only run them in class A. I generally bias with IAC adjustments but sometimes fuel pressure.