How do I set/adjust the bias on my tube amp?

New to tubes here. I couldn't find anything on the site on this. How do I adjust the bias for my 300b amps. What guage do I need? How do I determine the setting for the tubes I have? (Electro Harmonix).
There are various schemes for bias adjustment and many amps are self biasing. It really depends on the amp, not the tubes. Contact the manufacturer for their recommended procedure. Or let us know what amps you have and perhaps someone here is familiar with them. If any type of test equipment is required it is usually a common voltmeter.
Myraj, Herman is 1000% correct. I cannot add anything to it. You need to list the amplifier.
Herman & Trelja,
It is a pair of custom made 300B monoblocks by Kevin Brooks. There appears to be a bias adjustment screw by each 300b tube.
Your comments and help are appreciated.
I have never been 1000% percent correct before. I am very proud.

CAUTION: The voltages you are dealing with are very dangerous.

The following applies to typical SET circuit topology. Since I am not famliar with these amps it may not apply. There should be a resistor in the path between the cathode and ground. The cathode leads are the larger pins. If you measure the DC voltage across this resistor and then divide it by the value of the resistor it will give you the bias current. I would think somewhere around 50 milliamps (.05 amps) but it really is dependent on the design of the amp. Some amps have small jacks where you insert your voltmeter probes so you do not have to open the amp. The designer will then specify a certain voltage for the adjustment based on the value of the sense resistor and the desired current.

If too low you will clip the signal during loud passages. Too high will cause the same problem and also cause the amp to run too hot.

It would be best to contact the designer and get his recommended procedure and bias level.
Well, lightning strikes twice Herman.

You are again 1000% correct. Very good advice you gave, and as I don't know anything about the amplifiers listed, the line about contacting the manufacturer is key. 50 mA may be a good starting point. Or, it may not be. You should really ask the designer if at all possible.

I often like to set bias on the high side, as I find it imparts a lusher, tubier sound. Of course, you will go through tubes faster. Some people don't have that taste. Use the manufacturer's specs as your baseline, and then play around a bit later to learn more about your amps.

Myraj, some amps are to be biased using current, some voltage. The tube does play into things, but the design of the amp itself comes first.

Some amps are autobias(very easy, but not always best if you want to run different output tubes), some like Conrad Johnson use an LED/srewdriver(very easy), my Atma Spheres have an easy way which would take too long to go into here, maybe the majority of amps require you to hook up a volt or ammeter and perform the adjustment(like your amps), and then there is my Jadis. While most Jadis are autobias, I have a brilliant system where I need to take the amp apart, use two meters, adjust one setting, do the other(which throws off the first), then go back to the first, then the second. Ah, the French...
Even though tube amps are relatively easy to bias (a small flat head screwdriver and voltmeter are really all that's needed), manufacturers nowadays can insist you send them the amp for biasing. Probably to protect their warranty but most likely an edict from their lawyers. Keep in mind that the mains in a tube amp run anywhere up to 600 volts DC. Yes, amps are well designed and biasing is a rite of passage into tubes (once upon a time) but you should contact the mfr's tech support before you try anything.