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

D Rock 247

D Rock 247

Guest
Dec 24, 2016
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20
#1
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
 
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#2
D Rock 247 said:
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
Click to expand...
How do you know the tube blew as a result of your settings?
 
#3
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
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.
 
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#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
D Rock 247 said:
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
Click to expand...
One more question: What do you do with all the extra time you save by not spelling out "you"?
 
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#7
rodl2005 said:
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
Click to expand...
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.
 
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#8
BassmanPaul said:
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.
Click to expand...
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
D Rock 247 said:
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.
Click to expand...
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.
 
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#11
Munjibunga said:
@agedhorse
Click to expand...
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.
 
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#12
agedhorse said:
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, a
Click to expand...
... and there you are.
 
#13
agedhorse said:
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.
Click to expand...
Just curious - what is B+ for the KT88s in the Prodigy?
 
#14
Munjibunga said:
Just curious - what is B+ for the KT88s in the Prodigy?
Click to expand...
Don't have the paperwork here, but "f'ing high" would suffice. Higher than any tube amp I have designed, anyway ;)
 
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#16
Korladis said:
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.
Click to expand...
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?
 

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