Mark IV Problem - Volume Drop & Tube Questions

[darkalone]

Acquired a Mark IV roughly 4 months ago. Got it used, and the prior owner had no idea when the tubes were last changed. But it worked and sounded kickass (http://www.youtube.com/watch?v=Qkuxind8E7A ).

Up til today that is. Fired it up, and found the volume across the board is just gone, like barely audible, even with the master cranked. I have to suspect it's a tube issue. The question is which one? And given the unknown age of the tubes in it, a full re-tubing is almost a certainty for me at this point.

So that leads to the question of what sort of tubes to put in it, and whether or not to go with a mix of 6L6 and EL34s, or just stick with the all 6L6 configuration. Also, I discovered one of the preamp tubes was a 12AT7 as opposed to a 12AX7. Is this normal? Is that something I should stick with when I re-tube? Or should I just run all 12AX7s across the board?

Any help you guys can offer is appreciated. Thanks.

 

[bgh]

I have EL34s and 6L6s in mine. I love the way it sounds in tweed power and class A.

Concerning the pre-amp tubes, mine are all 12AX7s.

 

[swbo101]

Mark IV 'A' revision models have 1 12AT7 in the V4 slot which is the reverb driver. You should NOT put a 12AX7 there. In the 'B' revision of the Mark IV, they are all 12AX7s.

I am also currently running a combo of 6L6/EL34, but from time to time I do go back to all 6L6s. Just a matter of taste.

 

[bgh]

Never knew that about the rev A. Thanks!

 

[darkalone]

Well... I guess I can safely say it's not the tubes. Just installed all new tubes and the volume issue is still there. And the output I do get from any channel is fuzzy and brittle.

Any other thoughts on what might be going on?

 

[darkalone]

Just a quick update. Back from the shop. Turns out it needed a replacement resistor in the drive stage. Back up and running, sounds fantastic.

Now I have a mystery issue with my TriAxis/2:90 rig... Oy vay. :lol: