problem with mark iv power tubes

[harry manback]

hey guys. lately, i've been having problems with the power tubes in my mark iv. it seems that the heaters are not getting hot when i turn it on (standby or not). the preamp tubes heat up fine, but no matter what i've tried the power tubes just won't light up. every now and again, they'll come on for just a few seconds, and then die again. i've tried changing the tubes around, and swapping them out, and i've also wiggled them (just a little) when on standby, but to no lasting effect.

anyone have any ideas? i've already called mesa, but they haven't gotten back to me yet.

thanks again

jeff

 

[Boogiebabies]

Jeff,


Does the amp work?

The preamp heater voltage is run off the same 6.3V power supply as the
power tubes.

What year MK IV is it as well?

 

[Boogiebabies]

Double post, Sorry.

 

[harry manback]

i found and fixed the problem, but i'll let you guys know what happened for future reference.

the power amp tubes weren't heating up, but preamp tubes were, including the phase inverter. i talked to Mesa, they said that it was a failed power rail (or wording similar to that) and that i should bring it in to their local tech and he'd get it up and running in no time. i've done a few electronics repairs, and know my way around with a soldering iron and VOM, so i decided to take a look myself, before bringing it in. opened it up, found the power rails for the heaters, and lo and behold, a solder joint had cracked on one side. so, broke out the ol' iron, and voila! good as new. the problem initially presented itself as the amp working fine, then fading to nothing. i could wiggle the tubes, and eventually, they'd come back on for a while, apparently until my cabinet vibrated the amp enough for the joint to come loose again.

my question now is this: i had been running it with the tubes that were in it when i bought it (used). el34 and 6l6, like usual, but until yesterday, i hadn't really noticed that the el34s were not from the same color batch. one was tan, one was white. i'm wondering if, as the tubes aged, that maybe they weren't balanced enough, and one started drawing more current than it should, including the heater, just to keep up?

thanks for the help guys, i appreciate the responses.

and also, A+ to mesa customer service.

 

[Monsta-Tone]

Glad you got it fixed.

I don't think that the tubes would have caused the solder joint to fail. It's more likely a heat or vibration issue.

 

[harry manback]

Glad you got it fixed.

I don't think that the tubes would have caused the solder joint to fail. It's more likely a heat or vibration issue.

thanks for the info. that's what i'm starting to see from reading up on the subject a little more...

i do have one more question for you guys, though. do you usually use Mesa's tubes, or do you get a tube supplier to just match some up for Mesa's preset bias? i've been itching to try JJs and some SEDs in this bad boy, and now that i've got the kinks worked out and (kinda) learned how to get what i want out of it, i'm ready to see if there is even more to be impressed with.

thanks again for the help,

jeff

 

[Monsta-Tone]

Bob at EuroTubes will hook you up with JJ's. I personally don't like the Mesa Preamp tubes, but lots of people do. I use them for FX Loops & Reverb, and that's about it.

http://www.eurotubes.com/index.htm

 

[harry manback]

Bob at EuroTubes will hook you up with JJ's. I personally don't like the Mesa Preamp tubes, but lots of people do. I use them for FX Loops & Reverb, and that's about it.

http://www.eurotubes.com/index.htm

thanks man. i really appreciate the hookup. i'm getting excited already, and i haven't even looked yet.....

 

[Boogiebabies]

Bob is a good guy, but he does not like anything he does not sell. He is a business man. Other than NOS, he only pushes JJ's. The JJ 6L6's are good sounding tubes in MK series amps, but I prefer the GT E34L over the JJ. It is designed with larger heat wings and are designed much more like the original Tesla.