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Am I seeing this correct? Peavey VTM 120 standby voltages

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  • Am I seeing this correct? Peavey VTM 120 standby voltages

    I'm just re-tubing this amp for a friend and was taking a voltage reading
    on the output tube plates and noticed that it had ~525VDC on the plates
    even in standby. I didn't think that was right, so I checked the preamp
    plate voltages but they switch off and on with the standby.

    Looking at the schematic: (http://www.schematicheaven.com/newam...vy_vtm_120.pdf)

    -it appears that this is how the amp was designed to operate. V5-V8 plates
    always socked with the full B++ while the V5-V8 screens and the pre-amp
    plates are switchable with the standby.

    Am I seeing that right? Do you think this is ok? I have seen a few debates
    about whether or not standby is really needed, but it seems manufacturers
    have just always had the standby linked to the plates no matter what.

    Is this kind of a unique design or am I seeing this wrong?

  • #2
    If that's how they (Peavey) did it then yes, it should be that way. And it seems like a fine way to do it. If you pull the screen voltages on a pentode no current flows so as long as the Vp doesn't exceed the plate rating (by too much) there should be no consequences. I thnk it's fine.

    Chuck
    "Take two placebos, works twice as well." Enzo

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "If you're not interested in opinions and the experience of others, why even start a thread?
    You can't just expect consent." Helmholtz

    Comment


    • #3
      PV isn;t the only company that does this, but it is how PV does it on most if not all of their tube amps.

      This is perfectly fine. As Chuck said, if the voltage is removed from the screens, the tubes won't conduct.


      Contrary to the thoughts of many people, the purpose of the standby switch is to allow the amp to remain warm and ready but silent, it is not primarily about removing voltage. Removing high voltage completely - as done on many amps - certainly does that, but so does this method. Other methods you see involve things like leaving the voltage on altogether, the switch shorts the opposing power tube grids together, thus killing any signal. Some amps open the cathode connection for the power tubes, which also kills any conduction through them.
      Education is what you're left with after you have forgotten what you have learned.

      Comment


      • #4
        Thanks for the explanation guys. I just haven't seen this before, but it makes sense now.

        Comment


        • #5
          hi, im new here and i have a vtm 60 head. i recently had a volume drop and the gain isnt as good as it was. all the tubes are new, the compression dip switch isnt working either as it had before, i dont know anything about repairing what might be wrong, what should i check for? any help would be awesome, thx. aaron.
          Peavey Triumph 120/ Valveking 100 Heads

          Comment


          • #6
            Hi Aaron, welcome to the forum.

            May I suggest you start a new thread for your amp. This thread has been dead over a year, and it is about standby systems, which your problem is not.

            Take a spare guitar cord and plug into the FX send, and plug the other end into the FX return. ANy help?
            Education is what you're left with after you have forgotten what you have learned.

            Comment

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