I know better than to ever run an SVT with out it plugged into the cab. So here is what happened...I plug in my Peavey Fury Pbass for some bedroom jamming. Running an 89' SVT-II non-pro through an 810E. Wanted to set some levels on a pedal. Well...no sound. So I freak out, and check a lot of things. Not thinking I through it on standby, and unplugged it from the back of the speaker to check the connection. Well...this is funny...turns out my volume was all the way down on my bass. Anyway, I have heard and read many stories about the SVT frying tubes and output transformers when running without a cab connection. So far, so good its running. Just hoping I didn't create any problems that could linger in the future.
I was always under the impression that if an SVT was even on without being plugged into a cab it could damage it regardless of whether a bass was plugged in or not.
Exactly what would it take to do damage to an SVT all tube amp in order for it to damage from not being plugged into a speaker?
Tube amps Need to be connected to a load when switched to operate. Not doing so can cause damage to the OPT and the output tubes from operating into an infinite impedance. It’s why many tube amps short the output when nothing is plugged into the speaker outs.
The tubes can flash over instantaneously, especially with modern crappy tubes in vintage amps. Some modern amps have reverse diodes from the output tube plates to ground to help prevent the high voltage from exceeding the normal values which can happen when you whack the output transformer when its not properly loaded. In any case flashover can blown the high voltage fuse (if any) and/or the screen resistors (which are supposed to be special fusible ones).