The Power Brake is a different thing, its attentuator, it allows you to crank up the entire amp (the power amp as well), including amps with master volume.

It is possible to add a master volume to the thing (that would allow you to crank up the preamp while keep the poweramp down low).
edit: though don't go ripping up an original plexi era marshall!!
a JMP or a JCM800 without the master volume is acceptable though

all you have to do is add a 1M audio taper pot as a volume control after the treble pot before it goes into the 22nF cap and the next stage of the amp.
Get an amp tech or someone who is proficient with electronics to do this for you since tubes amps have got dangerous high voltages in them and if you don't feel safe poking around in them its probably not a good idea.
Last edited by seljer at Jun 29, 2006,