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Help!!! Mesa 400+ Fuse/Tube issues

Discussion in 'Amps and Cabs [BG]' started by brett7276, Apr 22, 2009.


  1. brett7276

    brett7276 Supporting Member

    Jan 14, 2009
    Indianapolis
    Tonight I retubed my Mesa 400+- it was working fine prior to retube, its just that the tubes had a lot of hours on them, so I thought I'd go ahead and retube it prior to our next show. I ordered and installed new JJ's from eruotubes -all correct 6l6GC's and EC83s for preamp. The amp is VERY clean and spends most of its time in a sealed rack case- so dirt in the sockets is likely not the issue- When I powered up the amp I of course kept it on standby- let it run that way for about 10 min or so. Initally I heard some scracthy/staticy types of electical noises that were very quiet through the speaker but went away after the first minute or so, so I assumed it was just part of the burn in process. After about 10 mins pluged my bass it and fipped the standby...tone was kind of wierd sort of rubbery- then output droped by half, and second later, lost power and fuse was cooked...SLIGHT oder of something burned detected- buts was not the usual buring wire smell... anybody got any idea what my issue is?? before I drop cash on taking the amp to a tech? any help is much apprecatied.
    Thanks,
    B
     
  2. Put your old 6L6's back in and replace the fuse. If the amp fires up okay you suffered a new tube failure, most likely cathode to heater short. The amp should still be looked at as shorted output tubes can over-stress other componets.

    Jon
     
  3. brett7276

    brett7276 Supporting Member

    Jan 14, 2009
    Indianapolis
    thanks I'll try that ...so its power tube failure??
     
  4. Sounds like it, one of our guitarists builds his own amps and just had this happen with EL34's. Not saying it is a failure that happens often but the noise in standby is a big clue.
     
  5. Hi.

    ^+1. Test with the old tubes to see whether the amp still works.

    While tube changing is straight forward procedure, a tech with proper knowledge and equipment can test each tube prior installing, have the amp hooked into into the test equipment while powering up, bring the voltage up with a variac (mainly if changing caps) etc. so it's not necessarily a bad idea to let a tech to change tubes.

    Even though the experts have said that tube change had nothing to do with it, I have had a few instances when old filter caps have bitten the dust spectacularily when powering up fresh tubes for the first time.

    In any case, even if the amp works with the old tubes, I'd take it to a tech to be sure.

    The tubes themselves are electromechanical devices, and quite prone to breaking when handled roughly. It's not anyones fault, it's just the nature of the game, IMHO.

    Regards
    Sam
     

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