[ColinTheAmpMan1]

I have just had another look at your post on the design of an AC10 Twin clone. I wouldn't bother with a master volume if I were you. Most of the circuit designs for master volume controls are not very good and require a relatively expensive twin-gang potentiometer. For one thing, they pretty-much eliminate the possibility of pushing the output valves and it is output-valve distortion that is the most desirable. Just having pre-amp valve distortion is a bit pointless, IMHO. The ten watts that two EL84s are putting out isn't ear-splittingly loud anyway and since they are capable of getting close to twenty watts, the channel volume controls will have pretty much the same effect as a master volume. As there is no negative feedback in the AC10 circuit, you can't put in a "presence" or "mojo" control either. I would look for a power-brake circuit. This goes between the output transformer and the speaker(s). You could either buy a ready-made one, or find a circuit and build one yourself. Augmenting this with an overdrive pedal will get you the best of both worlds; pre-amp valve overdrive and power-valve overdrive. That way, you can get the output valves singing as much as possible and throttle back the overall volume.
I might have some circuit ideas for power-brakes.
Colin.

PS: A presence control takes the feedback signal to ground progressively via a capacitor and potentiometer, while a "mojo" control reduces the feedback signal by the agency of a fairly large variable resistor. They have similar (but not identical) effects.