Mark V - Sound/tone fade issue

[fjk1138]

Hi,

My Mark V Ch3 will play fine and suddenly it's like someone goes over to it and starts turning the volume and tone knobs down. It sounds real weak for a few seconds and then comes back full force and is fine. I play CH3 on Mark IV mode more than anything, so I don't know if the other channels are affected.

I have moved every cord in and out of their jacks several times, the FX loop is off when it happens, and the amp was brand new in July 2010.

Is this a tube issue, and if so any idea which position? Thanks to anyone who can help.

 

[fjk1138]

Update - it appears that Ch 1 & 2 are affected in that they play fine, but seem to be quieter than before. Any idea if this would be faulty 6L6's?

 

[ixoye777]

No idea but as a word to the wise you should always have a spare set of tubes lying around for troubleshooting purposes. Snag a set of power tubes and at least 2 preamp tubes. 90% of the problems tube amps face are tube related.

 

[fjk1138]

SOLVED - it was at least 1 faulty 6L6. I put in 4 new ones and the Mark V sounds supercharged now.

 

[fjk1138]

UPDATE - NOT solved. Just happened to me a few mins ago again and is now fine again. After replacing the 4 power tubes at the end of February, all was well until today.

Just some more thoughts on this:
1. I keep mine fairly quiet, and I have one Digitech delay and tremolo pedal in the FX loop. The FX loop is usually off, with just the reverb on, but I am using the Output
as a Master Volume knob. My individual channel volumes (clock positions) from Ch 1 -3 are 11, 9.5, 9.5...and the Output is just under 9. Am I keeping the
Output just low enough that it might be cutting off the volume?

2. Just prior to the volume problem (as in just mere minutes before), I had the reverb off but the FX loop on. I played with the delay on for a few minutes, then turned the Reverb back on and the Loop off before it happened. Should I try replacing V4, V5, or V6 to see if that helps?

 

[screamingdaisy]

I've read that volume fluctuations like that are usually preamp tube related, although I've never experienced it myself. On a Recto, it's normally related to the tubes in the cathode follower positions failing due to the high voltages involved, however the Mark V doesn't have any cathode followers so...

Long story short, in theory it could be any tube that's active in all three channels, thus my best guess is to swap out those preamp tubes one at a time with a known good preamp tube until the problem goes away. It's kind of tedious, but that's one of the joys of owning a tube amp.

Alternatively, if you have more money than patience you can retube the whole preamp and keep the used ones as spares.

 

[fjk1138]

I've got 3 new preamp tubes, so I guess I've got my work cut out for me.

Thanks for the help, I will report any progress (good or bad).

 

[boogieman60]

Might be the rectifier tube...mine went and the amp got very quiet. It is always in the curcuit..I think for voltage reasons...any comments? I know my amp won't work without it..regardless of the position of the tube/diode switch.

 

[fjk1138]

Might be the rectifier tube...mine went and the amp got very quiet. It is always in the curcuit..I think for voltage reasons...any comments? I know my amp won't work without it..regardless of the position of the tube/diode switch.

I wondered about the Rectifier tube also. I just got of the phone with Boogie and they said that the Recto tube should not really be a factor since I am running it in 90 watt mode on each channel. Instead they recommended that I put it in hard bypass mode and play it that way for a while, which I am trying now...

 

[d77e]

Try cleaning the input jack, with contact cleaner. Or send a email to Mesa/Boogie. They respond very fast.

I Have had this issue in a Recto Preamp.

 

[fjk1138]

Last night, it really faded out bad and would come back to normal after a few seconds and then fade back to sounding like it's got a pillow over the speaker.
Seems to be limited to CH 2 & 3.

It's not the guitar, input jack, or the cables (I've swapped and/or cleaned multiple times). I have even tried different cabs and speaker cords, but no luck.
After talking to Boogie and the store where I bought it from, I decided to forgo trying the tubes and took it in to be looked at. Will post the result.

 

[fjk1138]

Store has informed me that they are not hearing the problem. They will test it instore when they get it back from the tech.

The only other questions I can think of at this point (though I'm ready to give up):
1. Could it be the cab, speaker, or the wires between the cab's input jack going to the speaker itself?
2. Would Mesa exchange it for a new Mark V if no one can identify the problem?

 

[screamingdaisy]

The speakers/cab/cable seems unlikely, although I suppose it could be possible. Not sure why it would be limited to channels 2 and 3 if that were the case, but you never know.

One of the members on this forum had his amp replaced after a number of unsuccessful attempts were made to repair it. You may have to be patient and work you way through the process however.

 

[scoden]

I had the same issue.....posted about it recently. After troubleshooting very systematically, turned out to be V4 .
These issues are almost always tube related. I wouldnt bring it to a shop unless I exhausted all tubes first.

Good Luck.

 

[fjk1138]

I had the same issue.....posted about it recently. After troubleshooting very systematically, turned out to be V4 .
These issues are almost always tube related. I wouldnt bring it to a shop unless I exhausted all tubes first.

Good Luck.

I am sorry that you had a similar problem, but I am thankful that I am not the only one with this type of problem, as it confirms that I am not hearing things.
Speaking of hearing, that's also one of my fears - the tech's ears may be worn out to the point that they cannot hear the tonal difference when the problem occurs.

Anyway, I am hoping that I will be able to try it at the store in the next couple of days - will post the results again. I really hope this can get resolved soon - playing
through a Roland cube amp is sadly uninspiring.

Thanks again to everyone who has responded so far.

 

[PinkFlydxx]

I have also had this problem. I know it occurs on at least a couple of channels. When it does, the volume will drop out and then very quickly come back. It is an odd occurrence as it takes some time with the amp on and playing for it to occur.

It will happen intermittently and takes some time for it to start - therefore it may difficult for a technician to play it long enough for it to happen so that they can diagnose the problem. The tech would have to be aware that it may take a while for the problem to occur (at least with my amp). I have also noticed that in some instances, the sound will get very "flubby". I'm not sure if this is cased by the same problem or not.

I have changed all the power tubes and the rectifier tube, but the problem did not go away. I now have a full set of preamp tubes. I have not tried replacing tube #4 only first, but I believe I will give it a try and just hold all my other tubes back. If this does not work, then I'll add a tube each time and see what happens.

If I find a fix (by changing tubes) I will post it here. Please do so if you find the cause and solution. Thanks.

 

[Adambomb]

Just plug in your amp and pull one at a time each preamp tube with new one and that might fix it. Don wanna spend over $100 just for a tech to pull out a tube and put one back in. It would be like somebody paying me to screw in a light bulb. Don't be scared to work on your tube amp man cause like everybody is saying, it's usually 90% tube related problems. And it's also fun to work and learn about the amp. I'd go to the shop and get that amp back and try all the preamp tube swappin one at a time if I were u man.

 

[BostonRedSox]

Just plug in your amp and pull one at a time each preamp tube with new one and that might fix it. Don wanna spend over $100 just for a tech to pull out a tube and put one back in. It would be like somebody paying me to screw in a light bulb. Don't be scared to work on your tube amp man cause like everybody is saying, it's usually 90% tube related problems. And it's also fun to work and learn about the amp. I'd go to the shop and get that amp back and try all the preamp tube swappin one at a time if I were u man.

Ha, ha -- is your name your way of paying homage to the wrestler Adam Bomb?

 

[fjk1138]

It will happen intermittently and takes some time for it to start - therefore it may difficult for a technician to play it long enough for it to happen so that they can diagnose the problem. The tech would have to be aware that it may take a while for the problem to occur (at least with my amp). I have also noticed that in some instances, the sound will get very "flubby". I'm not sure if this is cased by the same problem or not.

I have changed all the power tubes and the rectifier tube, but the problem did not go away. I now have a full set of preamp tubes. I have not tried replacing tube #4 only first, but I believe I will give it a try and just hold all my other tubes back. If this does not work, then I'll add a tube each time and see what happens. Thanks.

My problem originally took about 15-30 mins to occur, but the failure now happens in a matter of a few mins. I never had the flub problem though. I cannot try swapping anything because the store still has it, though they claim they will try to make the amp fails since the tech could not get it to do it. My fear at this point is that I could completely retube it and still have to send it back to Mesa (which is basically my next step), and if that fails I am switching brands.

Pink Floyd - If you have any luck, please let me know or send me a message.

 

[Adambomb]

Just plug in your amp and pull one at a time each preamp tube with new one and that might fix it. Don wanna spend over $100 just for a tech to pull out a tube and put one back in. It would be like somebody paying me to screw in a light bulb. Don't be scared to work on your tube amp man cause like everybody is saying, it's usually 90% tube related problems. And it's also fun to work and learn about the amp. I'd go to the shop and get that amp back and try all the preamp tube swappin one at a time if I were u man.

Ha, ha -- is your name your way of paying homage to the wrestler Adam Bomb?

Hahaha, no. But is that ur amp with the fade issue? Have u tried all the preamp tubes brother? (hulk hogan)