Mark Iv b. losing volume

[major7th]

I just retubed my mark iv rackmount head 2 weeks ago and ever since, after about 2 hours of playing at moderate volume, 3-5 on master, I lose 80% of my volume.

If I turn the amp off and back on, it regains volume, but sometimes loses it again.


Any ideas?

 

[topcat0399]

Try putting the old tubes back in and see if the problem continues. If not - start swapping in the new tubes one by one and test to see if it happens.

When/If it does you found your problem.

If not - do your pots need cleaning?

Moderate volume: 3-5!!!! good god; none of the clubs we play would ever allow us back if our band played at that volume.

My Mark Iv lives in class A tweed most of its life with master between 1-2. Closer to 1 because this thing is LOUD!

I also enjoy the sound man actually putting me IN the PA. :lol:

 

[topalchohol]

Try pulling out all the tubes and reseating them. Otherwise you've got a weak tube or possibly a tranformer problem. I had an amp that did that same thing and each time it took less and less time. Finally the transformer took a dump. Good luck.

 

[jpdennis]

Try pulling out all the tubes and reseating them. Otherwise you've got a weak tube or possibly a tranformer problem. I had an amp that did that same thing and each time it took less and less time. Finally the transformer took a dump.

One of the symptoms of the power transformer I had replaced in my Heartbreaker. But, then again, the tubes are always the easiest "first line of defense" test. This board has taught me to do as much as I can. I even go so far as to remove the chasis from the cab and use the "chopstick method" to every component as well as the tubes. But when it comes to using and properly reading a multi-meter for all the circuitry, well "Hi ho, hi ho, off to the shop it go ..." :lol:

"A man's gotta know his limitations" ... Dirty Harry 8)

Dennis

 

[Rob Lockwood]

In my experience fault finding anything if you do something (i.e. remove and replace tubes) and very soon after there is a problem that wasn't there before the chances that it is not caused by the thing you just disturbed is pretty low so I wouldn't worry about your transformer too much yet, although its a possibility. I would go with either a bad connection at the tube sockets or that one of the new tubes has a fault.

Did you do pre amp or just power - when I have had fading volume it has been a pre amp tube issue. If both you can find where the problem lies by plugging into effects return when the volume is gone. If you get more volume this way than in the normal input problem is in the preamp. You could try it when the amp is working ok to see what should happen.

I suggest to put your old tubes back in. If problem is gone, probably the tubes but could still have been a connection issue. Then if you put the new ones back and the problem returns it must be the new tubes.

 

[swbo101]

Had a similar situation with my Mark IV a couple of years ago. Kept replacing the V1,thought that was the issue. Ended up being the low voltage regualtor.