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Blew a kt88 in a mesa four 88......

Discussion in 'Amps and Cabs [BG]' started by D Rock 247, Jan 1, 2017.


  1. D Rock 247

    D Rock 247

    Dec 24, 2016
    Yep. In socket v7. Never had any tube failure before in all my guitar or bass amps but four 88 owners beware: dont go all out on half power on a powerhouse 212 cab. If u do make sure your bass nob is not is not cranked on channel voicing 1. Ph212 was a cab i just bought. 8 ohm. Yes i put the load into my 4ohm input at half power. (as stated in the manual) what i was wanting to achieve is somewhat impossible but was trying to get gut wrenching lows out of a 212 (somewhat possible at a lower volume) but when u want to play at a loudness of atleast a 6x10 through a 2x12 lookout!! Lol. Scared the crap out of me. Anyway, quick q, just making sure what kind of slo blo fuses are in yalls prodigy Mine was a 250v 5a. But new tubes are getting shipped, along with some 12at7s im gonna throw in there for giggles- and carefully check the bias.... happy playing guys. I made a boo boo and figured id pass it along to my fellow all tubers. Looks like im wearing the dummy hat today. Peace. D
     
  2. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    How do you know the tube blew as a result of your settings?
     
  3. D Rock 247

    D Rock 247

    Dec 24, 2016
    Cause u cant pump your volume at about 125w on only two kt88s? I dunno. I know the tube is gone. U could shake the tube, and it was tinging. Rest wernet as hot. Hell u could see it through the amp dude. Blue led quickly turn bright ass orange with a nice pop from a sli blo. Read the manual and they said theyve had a problem when creating the bass prod amps that hard low end bass notes make em start poping tubes at half power. I prob leave it on 250w from now on since its only on 4 power tubes as supposed to a 6x6550s in a 300w svt. But so far it whoops tail in tone but gonna fender it up with some 12at7s to get rid of some of that extra fuzz i dont like. I squeeze all the grunt i need through banging the crap out of those bass strings. Ill just do it myself, easy to bias, blow another one and send it back to mesa....lol
     
  4. BassmanPaul

    BassmanPaul Inactive

    I don’t think that the Mesa Warranty covers abuse!

    A pair of NOS KT88 with fixed bias and enough B+ should deliver around 100W clean. Distorted, 125W should be relatively benign.

    Meaning no offence, but folks who design these products try to anticipate everything that an owner can do to their amps and factor that into the design. I have seen so many amps that have been “improved" by their owners into a pile of messed up electronics. This is especially true for tube amps where folk consider themselves expert. The voltages these amps operate on make it extremely easy for the output stage to lose control and run away.

    Tube swapping is a big thing in the guitar amp world. In ours it can produce unanticipated results and failures.
     
    Sartori and Munjibunga like this.
  5. I've never had any probs swapping pre amp tubes - 12++7 to other 12--7s as long as they're like minded tubes. . 12ax7 to at7 or au7 I swapped the 2 pre tubes in my Super Bassman with 5751s works a treat.
    I HAVEN'T taken power tubes outta the equation tho. Never had an amp that could cut 2 or 4 of 6 etc. ..
    I'd imagine that's a different ballgame
     
  6. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    One more question: What do you do with all the extra time you save by not spelling out "you"?
     
    aproud1, Microbass, tfer and 11 others like this.
  7. D Rock 247

    D Rock 247

    Dec 24, 2016
    Ive got more mesa matched kt88s comming. 12at7s are also mesa. That half power settinf has really got me wondering if the trannys putting out too many volts to the two tubes. On all 4 at full power they seem to be fine at a very loud volume. Either way im gonna call mesa tomorrow just to s
    Get some info. Ive already talked to the guru who usually repairs my amps and he agreed if any more tube problems, back to mesa it goes. But yes im kinda excited to swap some preamp tubes so i can tame some of that wooly booger.
     
    Sartori likes this.
  8. Korladis

    Korladis Inactive

    Yeah, and while I'm not a Prodigy owner, I do have a Mesa D-180, and it's a tank. I play it loud, too, going near full power lots of the time.

    I have had to replace output tubes twice in the six or seven years I've owned it, but that happens.
     
  9. Korladis

    Korladis Inactive

    I mean, fact is that tubes won't last as long if you're blasting them all the time. That's why I don't buy great, NOS power tubes. I know that I'm going to blow out my power tubes eventually, so I kinda feel like if I used NOS ones, that would be taking away a chance for someone who maybe plays at less extreme volumes to use them for much longer.

    I might get some NOS preamp tubes, eventually, though, as those last a lot longer.
     
    /\/\3phist0 likes this.
  10. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    This is not one of my designs, but on general terms KT-88's have some unique properties but also require very high voltages in order to deliver these. Whenever ANY tube (not just the KT-88) is operating at very high anode voltages, any impedance mis-matching and heavy overdrive into a reactive load induces additional stress on the tubes. This can cause premature failure of a "weak" or older tube.

    This is not unlike a race car's engine (all high quality parts), which if driven moderately will last a long time BUT under racing conditions sometimes fail earlier than expected, and will never last as long as when operated moderately. The difference in lifespan can be 5x or more depending on conditions.

    IMO, you would have more lifespan margin under heavy overdrive conditions by using the complete compliment of tubes available.

    If your tech is a Mesa authorized service tech, he can receive support from our factory technical service and support techs. If not, I caution you that if the work done creates additional problems and your amp is still under warranty, there may be some additional cost issues for you to correct the damage as that kind of work is not warranty work.

    You might want to give out customer service folks a call first, to see what your options might be.
     
    GregC, blindrabbit, JGbassman and 7 others like this.
  12. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    ... and there you are.
     
  13. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Just curious - what is B+ for the KT88s in the Prodigy?
     
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Don't have the paperwork here, but "f'ing high" would suffice. Higher than any tube amp I have designed, anyway ;)
     
  15. D Rock 247

    D Rock 247

    Dec 24, 2016
    I was jamming with the guys at practice taking a 10 while i texd that. Sorry, bad habit i guess
     
    Munjibunga likes this.
  16. D Rock 247

    D Rock 247

    Dec 24, 2016
    Does your d180 have the built in eq? I know they made two types of them. Just wondering which one u have. (Just incase the prodigy dont pan out. Lol) whats that bad boy weigh?
     
  17. Korladis

    Korladis Inactive

    You mean the graphic EQ?

    It has a regular rotary EQ and a graphic EQ.

    Weighs something like 45 pounds without the case I made for it.
     
  18. D Rock 247

    D Rock 247

    Dec 24, 2016
    Not a bad weight for an all tube 200 watter. Yes, graphic eq. (Whoops) thanks.
     
  19. Korladis

    Korladis Inactive

    Yeah, but it's rackmount, meaning that it's very awkward to carry without a case. So it's really more than that.
     
  20. dbase

    dbase Gold Supporting Member

    Jan 3, 2008
    South Jersey, USA..
    Put in a 25 amp fuse, problem solved ;)
     
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
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