Major Mark IV help needed...

[Daxman73]

Hey guys and gals, I have a serious issue here or at least it's looking like one...I've never had this problem before on any amp, so hopefully there is some help out there for it...When I turn the stand-by switch on there is a pop/crackle/hiss/zap/hum sound that comes through the amp and then it goes away...That's the first problem...It's been farting out and crackling through the speakers, especially at higher volumes, so I assume the power tubes are just worn out right?...I had two older pairs that I have laying around, nothing that I would want in there permanently, but I knew they worked, and I stuck them in the middle sockets...They were Mesa STR 430's...On both accounts there was a loud pop/hiss/hum noise that came through the speakers, the channel lights would not work and the tubes that I put in there glowed a bright blue...When I put the amp back on stand-by, all that went away...HELP!!!...What could this be?

 

[trem]

What happened when you stuck those 430s into all 4 sockets?

 

[Daxman73]

I didn't stick them in all 4 sockets...The outer sockets have JJ E34L's in them...I just tried two at a time in the inner sockets...The only ones that would work, relatively speaking, and not have the described problem, we're the original 6L6's that were in it.

 

[EirikBrandal]

The blue lights are supposed to disappear when you pull standby.
What you're talking about is power amp problems, as far as I can tell.
Try without the El34's. I don't think the mark IV likes them. He killed mine.

 

[Restless Rocks]

The standby switch itself could be going out.

 

[ANIMATED SUSPENSION]

Does it make any difference if you run it in class A ? What about tweed or triode ?? Try replacing the preamp tubes one at a time too.

 

[#2121313]

I would suggest (if money isn't a huge issue), replace the 4 Power Tubes with 4 brand new/fresh tubes - 6L6 or EL34/6L6 combo what ever you prefer the Mark IV can handle it.

If the problem persists, try replacing the Pre-Amp tubes, go thru them one at a time. You can buy one new tube and lowly rotate thru the V1, V2 etc positions until the problem goes away.

You may want to have a look at the fuse, it may be on it's way out, you can probably replace that too at any point for a couple of bucks...I had a BRAND NEW Mark IV (3 weeks old) and it kept cuttin in and out, I brought it back to where I bought it and they replaced the fuse and it's been fine ever since!

Have a look at the tubes right after the problem occurs while the amp is still powered on, you can usually see the tube that is malfunctioning-may not glow, or glow less than the others or even go very bright and/or fade in and out going very bright to very dull - I've seen this happen twice.

Good luck!

 

[6L6C]

Since you have two power tubes that you know are good put them in the OUTER sockets and run the amp in class A you can leave the two inner tubes out. If your amp performs OK, yeah get some power tubes.

When you put the good ones in the outer inner sockets (like you did) you are still forcing the amp to use tubes that are in question.

As said by others could be preamp related also.

Bottom line if you start swapping tubes and see performance differences just go for a complete set. When I say performance Im really referring to the pops and hisses in your case

 

[Daxman73]

Guys, thanks a ton for the info and ideas...I'm going to try some of them right now actually...It just seemed weird to me that the old, used tubes in the inner sockets worked, but when I switched them out with two other sets, I had those problems...It just doesn't make sense...I am going to put a new fuse in it for safe measure, but how do I test the stand-by switch?...I know this doesn't always hold true, but all the tubes "look" fine and I did the tapping test and the only one that made any significant noise was on of the inner tubes and it wasn't dramatic or anything...The amp will get a complete re-tube, but I want to make sure that there isn't anything else wrong with it first...I check back, thanks again.

 

[Daxman73]

Ok, here's what I did...I set it to Class A and tried each set of 6L6's in the outer sockets (3 of them)...When viewing the amp from behind, every single tube, except for the EL34, that I put in the left hand end socket glowed blue...Every one and they got hot to the touch much quicker than the right side...Remember, I said earlier that when it was in Simul-class mode, the inner tubes glowed blue...But here's something funny...The problems that I mentioned above, the pop/hiss/hum/crackling, went away...I'm lost...It seems to me, taking an uneducated guess, that there is something more wrong internally as well as tubes...Any thoughts?

 

[ketiov]

Call Boogie, and maybe send the amp in to get looked over? It wouldn't hurt. I only paid $120 for them to look over the caps and replace a switch and a few resistors, and like $80 of that was labor, so if it's something small it shouldn't cost too much.