actually, I like Colin's method. Never thought of doing it that way. There is no danger, save for heat generation, as the CCS is dropping all of B+. For short period of time, it shouldn't pose a problem. Just be sure you don't try this from the mu output, as damage couldbe done the mosfets, and there is no way to get an real meanurement w/o including R3.
I am going to try this on my valve pre-where I can't test w/ a 9V out of circuit.
Thanks for showing me this method.
regrds,
Douglas