The answer tends to be different for different amps. Here's a brain dump.If I do not have service manual - I don`t know what do do with this pot.
1. Not all amps have a bias pot. The old Peavey PA amps had no way of adjusting bias. Some amps have a pot, but it's DC offset trim. Sometimes they have two pots, one is bias and the other is offset trim. Sometimes they have half a dozen and you need the manual.
2. BJT amps have emitter resistors and you can adjust the pot for about 10mV across each resistor. That's a good ballpark figure that should work for most output stages, erring on the cool side. Do this with the speaker unplugged. There's one resistor per transistor, so you can check them all to see what current each transistor is pulling, and find any unmatched ones. The 10mV figure applies to the hottest one.
3. Amps with lateral MOSFETs like the ECX... ones don't have emitter resistors. You have to break into the supply rail and adjust the pot for about 50-100mA per parallel MOSFET. 50 is probably better for MI/PA use.
4. Some BJT amps have bad thermal compensation, and if you bias them too hot they'll go into thermal runaway and blow up. There should be a thermal sensing transistor attached to the heatsink, or clamped to one of the main power devices, and you should make sure it goes back where it was if you replace the outputs. Lateral MOSFET amps don't have this thermal compensation, but ones made with vertical MOSFETs (like the Ampegs with their IRFP250s) should have it.
5. Most SS amps have so much negative feedback that they compensate the crossover notch. You'll never see it on a scope, you need a THD analyzer.
6. The only things that need matched are output devices that run in parallel. If you have 4 in parallel and one blows, you should really replace all 4 with matched ones, or at least ones from the same maker and batch.
7. Amps blow up for other reasons than bad bias.