Generally......
On a push pull Class A/B guitar amp, which you have, they use a common bias voltage, isolated from each half of the output with some decent size resistors - in the 220k-470k range. There's very little grid current, so the bias voltage can go thru the resistors with almost no I/R drop, but its enough to isolate the AC signals from each half.
Most larger amps have a bias control of some sort. Most do not require getting into the chassis to adjust. Some older Fenders in the late 60's up till early 80's had a bias "balance" whereby the overall level was set, but could be varied to "match" the two tubes. Most techs dont like that approach, prefer to use matched tubes, and convert the balance circuit back to overall level by swapping a few wires and adding a small resistor.
If you have one tube going red and the other not, its likely a bad tube or grossly mismatched tube, as both tubes receive the same bias voltage. If you blow a screen grid resistor, the tube will usually self destruct and you might have done that... reverse the two tubes, and see if the problem follows the tube.
Get or make a bias probe (PM me if you want one, I have a few left over). Use it with a cheap volt meter and set the level to about 35milliamps for a good ballpark middle of the road. Done. No need to go inside. No need to deal with danger. Takes like 10minutes. I'd bias amps FREE just to look over the rest of the amp for paying work... scratchy controls, bad jacks etc.