Need Help - Intermittent Volume Drop Problem

[PinkFlydxx]

I have a problem with my Mark V and would like to ask for your input. I've had my Mark V almost 15 months now. In the past few months I've noticed that while I am playing the amp volume will intermittently drop out for less than a second, then come right back up again. The drops are not isolated to any single channel.

However, a few nights ago, I also noticed that at one point the volume got louder, and started sounding extremely "flubby" - almost like a blown speaker (for lack of a better description of the sound). It has only done this once. However, this passed and the sound went back to normal, with the intermittent drop outs continuing. I also noticed that the speaker jack/cable area of the amp being very hot (it is plugged into the proper 8 ohm jack) - not sure if this is normal or a new symptom of a common problem.

I am currently running the following configuration (4 cable method with an added BBE Sonic Maximizer):
Fender Strat -> Nady wireless transmitter
Nady UF4 Wireless -> Digitech GSP2101 (Main Input)
Digitech GSP2101 (FX Send) -> Mk5 (Front Input )
Mk5 (FX Send) -> Digitech (FX Return)
Digitech (Output) -> BBE Sonic Maximizer (In)
BBE Sonic Maximizer (Out) -> Mk5 (FX Return)
Mk5 Speaker (Out) -> Speaker

I replaced all 4 power tubes and the rectifier tube with new MB matched tubes, but the drop volume problem continued, so I put the original tubes back in. I put new pre-amp tubes in the GSP2101 with no change. I've tried to "wiggle" the footswitch cable to recreate it and/or solve it but no change.

In trying to isolate where the problem may be, the next items I intend to check are:
1. Hook up guitar directly to the amp (hoping to isolate it just the amp, cable, or guitar).
2. Taking wireless unit out and hooking guitar up directly to the GSP2101,
3. Replacing every 1/4" instrument cable, one at a time
4. Cleaning all 1/4" inputs with electronics cleaner

It obviously could be in one of the many connections/cables/processors, and I hope to isolate those one by one, but I am more concerned with, and somewhat leaning towards, the problem being in the amp itself.

Could this possibly be a bad pre-amp tube? I have two new MB spares to change out but which ones should I start with? I'd rather not have to purchase 7 new pre-amp tubes, but if that's what it takes, then I will. I'd rather be absolutely sure before I lay out the money for 7 new tubes.

If you have any other ideas or suggestions on what could be the problem, please advise.

Also, any suggestions on how I may improve my processor/amp interface would be much appreciated.

Thanks for your assistance.

 

[Vogelsong]

Have you tap tested any of the tubes, that could give ya an idea.

You do have a lot going on there, good luck.

 

[PinkFlydxx]

Thanks. Yes, I have tap tested - but only with the protector caps on. I didn't get any unusual noise or drop offs in the sound. Should the tap test be done with caps off, or does it really matter?

PS: I read in the owners manual that volume swells could be a sign of power tube problems, but when I changed them out it didn't solve the volume drop out, and the swelling/flubbiness only happened one time (maybe more to come?).

 

[Vogelsong]

Thanks. Yes, I have tap tested - but only with the protector caps on. I didn't get any unusual noise or drop offs in the sound. Should the tap test be done with caps off, or does it really matter?

PS: I read in the owners manual that volume swells could be a sign of power tube problems, but when I changed them out it didn't solve the volume drop out, and the swelling/flubbiness only happened one time (maybe more to come?).

When I have tap tested it has always been with the caps off. They don't need to be tapped hard. If there is a bad one it won't take much and you'll know it.

 

[scoden]

try swapping out v4 v5 v6 one at a time .....I just had a similar problem and also switched out all the power tubes rectifier v1 / v7 still had problem

I replaced v4 and it stopped ..well I played it for about 4 hrs over two days and no sign of voulme drops so far.

Keep me posted on your results with a pm

 

[thalweg]

Anything further to report here. I'm having identical problem. Swapped power tubes v1 and v7. Suppose v4 next. But hopefully save some time if anyone has additional feedback?

I hate swapping tubes....I'd rather be strumming