Possible power amp problem? 3-channel Dual Recto

[dubs0587]

Every time I flip the stand-by switch on/off, it pops...not super loud but it's very audible and annoying! It didn't start popping until after I changed my tubes. I put a KT88/66 combo in(no pops), but I decided to go the EL34 route instead and it started popping...and it pops when switching channels, and I've noticed that the volume is starting to drop in and out...I've checked the tubes and they don't look like anything is wrong, but I could be wrong

And just about three weeks ago I bought two marshall 4x12s(1960a/b) and i've been running both cabinets. Coming out of both 8ohm jacks on the mesa, one into each 16ohm jack on the cabs. SAFE??? -- About a week ago it was making a really loud, low-frequency noise(almost like a motorcycle reving up in the distance), but it stopped all of a sudden and hasn't done it since.

Do I have a power amp problem? Anyone know what's going down?

 

[clutch71]

The volume "dropping in and out" sounds like volume swell to me which is a symptom of the power tubes going. Even if you bought them new, tubes can be a fickle thing. I've got new ones out of the box that were bad. GOod news, if they are new, you can most likely return them. If their not just put them aside for now and put the other ones back in. If the popping, channel popping and volume swell go away, there's your problem.

The low frequency noise your describing kinda sounds like preamp tubes. You can swap them out one at a time to see if this eliminates it with a new tube.

If it's a used head this might be your problem. I usually do a complete retube after about a month with a used amp.

You've got the proper set up for 2 16 ohm cabs.