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I accidentally unplugged my SVT-II (non)-pro from the cab while on standby. Kind of freaked me out.

Discussion in 'Amps and Cabs [BG]' started by TUEP, Oct 13, 2016.

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  1. Oct 13, 2016 #1
    TUEP

    TUEP

    Apr 8, 2007
    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.
     
  2. Oct 13, 2016 #2
    RoadRanger

    RoadRanger Supporting Member

    Feb 18, 2004
    NE CT
    If you had no signal going through it no prob.
     
  3. Oct 13, 2016 #3
    TUEP

    TUEP

    Apr 8, 2007
    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.
     
  4. Oct 13, 2016 #4
    BassmanPaul

    BassmanPaul Inactive

    Aug 25, 2007
    Scarborough Ontario Canada
    Yep, in standby the amp is doing nothing therefore no damage was done. :)
     
    Old Garage-Bander likes this.
  5. Oct 13, 2016 #5
    TUEP

    TUEP

    Apr 8, 2007
    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?
     
  6. Oct 13, 2016 #6
    BassmanPaul

    BassmanPaul Inactive

    Aug 25, 2007
    Scarborough Ontario Canada
    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.
     
    TUEP likes this.
  7. Oct 13, 2016 #7
    TUEP

    TUEP

    Apr 8, 2007
    Would this be something that takes seconds to happen or minutes?
     
    Dougie44 likes this.
  8. Oct 13, 2016 #8
    BassmanPaul

    BassmanPaul Inactive

    Aug 25, 2007
    Scarborough Ontario Canada
    Truthfully I’ve never tested it. I would think minutes.
     
  9. Oct 13, 2016 #9
    RoadRanger

    RoadRanger Supporting Member

    Feb 18, 2004
    NE CT
    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).