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

How do you know the tube blew as a result of your settings?

 

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.

 

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

 

One more question: What do you do with all the extra time you save by not spelling out "you"?

 

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.

 

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.

 

@agedhorse

 

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.

 

... and there you are.

 

Just curious - what is B+ for the KT88s in the Prodigy?

 

Don't have the paperwork here, but "f'ing high" would suffice. Higher than any tube amp I have designed, anyway

 

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.

 

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

 

Put in a 25 amp fuse, problem solved