GBE 750: how to replace a tube??

Discussion in 'Amps and Cabs [BG]' started by birdxofxprey, Jul 11, 2008.

  1. I think the tube in my GBE 750 is about dead - when I use the tube preamp I frequently get significant drops in volume that are immediately remedied if I switch to the non-tube preamp.

    I never had to change a tube. my questions:

    does the volume drop on the tube preamp indicate a bad tube?

    can I change the tube myself?

    must I use the same kind/brand of tube, or can I change brands (and if I can change brands, what do you recommend)?

  2. You need to take your GBE750 back to the dealer, or contact Genz-Benz direct.

    Pre-amp tubes last for years. Sounds like you've got a problem in the tube channel.

    FWIW, you can use any brand of 12AX7 tube that you like and to change it out should take no more than 5 minutes. The Genz-Benz install a "Ruby" brand tube in their amps when they leave the factory.

  3. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    It's possible that you have a bad tube, they are pretty mechanical devices and every once in a while they fail. Generally though, they should last a very long time.

    To change the tube, you will need to remove the retainer that threads into a mechanical standoff with a screw. Be sure not to unscrew the standoff by accident. I usually like to hold it with a small wrench or pliers to be sure it doesn't turn.

    Any problems or questions, feel free to PM me.
  4. ErnieD


    Nov 25, 2004
    please post back to what the repair was. I have the same amp and be nice to know this if I ever have to deal with it. Wonder if anyone here has this amp so they might open it up and offer some pics of the innards and maybe help this cat see what he should look for. Sorry Im away from home for a few days and dont have access to my amp or digicam. Good luck.
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