Mark IV picky about tubes compared to 5150?!?!!?

[bryan_kilco]

Ok, so I have a show in 2 days and I havent had the chance to order my new sets of tubes and money has been tight.....so, last night at practice, I did some tube swapping between the IV and 5150, only to find that the IV was really noisy (static-y/white noise) with any combination of tubes I threw in, even in Class A and I swapped them in/out to make sure.

I put the matched quad of GTs in the 5150, and not nearly as staticy/noisy.

Maybe my amp needs a good servicing?

 

[suhrlyguy]

White noise and popping/spitting is generally a preamp tube. If you tap the power tubes with the amp on, they should be quiet. If one causes a change in the noise or crackles, that's the one. Put the amp in standby and pull the tube (use a rag). Turn on the amp with a hand on the power standby switches and listen (the amp will hum slightly due to the imbalance, but the procedure will not harm the amp). If the noise is gone, the tube was your problem. If the amp starts to hotplate or short, shut it off immediately (this is completely from the manual).
Though if you changed power tubes and had the same problem, its probably a preamp tube. Start with V1 (manual page 17, see link below) and put in a known good one. Just repeat the procedure until you find the culprit.
I have had higher background noise associated with powerstrips. Not to underestimate different venues with their questionable electrical supplies. What was noisy at the gig turned out to be a wasted trip to the shop.
Most of this is covered in the mark IV manual from pages 17-19. http://www.mesaboogie.com/manuals/user_manuals.htm
Good luck