Mark IV Problem - Volume Drop & Tube Questions

Pre Recto days. Boogie modified Fenders, Mark I-IV, Dual Calibers, etc

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darkalone
Mark II
Posts: 64
Joined: Tue Sep 04, 2007 2:10 pm

Mark IV Problem - Volume Drop & Tube Questions

Post by darkalone » Sat Oct 26, 2013 2:33 pm

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
Mark III
Posts: 287
Joined: Tue Apr 17, 2012 10:01 am

Re: Mark IV Problem - Volume Drop & Tube Questions

Post by bgh » Sat Oct 26, 2013 9:29 pm

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.
Lefty guitars: Gibson SG standard (1977) • Gibson LP custom (1979)
Amps and such: Mesa Boogie Mark IV-B • Mesa Nomad 45 • Mesa TA-30 • Effectrode Blackbird • Kingsley Jester • AMT SS-11a • Zoom G5

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swbo101
Mark III
Posts: 447
Joined: Sun Mar 07, 2010 3:51 pm
Location: NY

Re: Mark IV Problem - Volume Drop & Tube Questions

Post by swbo101 » Mon Oct 28, 2013 11:00 am

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.
1991 Mark IV A

bgh
Mark III
Posts: 287
Joined: Tue Apr 17, 2012 10:01 am

Re: Mark IV Problem - Volume Drop & Tube Questions

Post by bgh » Mon Oct 28, 2013 12:22 pm

Never knew that about the rev A. Thanks!
Lefty guitars: Gibson SG standard (1977) • Gibson LP custom (1979)
Amps and such: Mesa Boogie Mark IV-B • Mesa Nomad 45 • Mesa TA-30 • Effectrode Blackbird • Kingsley Jester • AMT SS-11a • Zoom G5

darkalone
Mark II
Posts: 64
Joined: Tue Sep 04, 2007 2:10 pm

Re: Mark IV Problem - Volume Drop & Tube Questions

Post by darkalone » Mon Nov 04, 2013 6:09 pm

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
Mark II
Posts: 64
Joined: Tue Sep 04, 2007 2:10 pm

Re: Mark IV Problem - Volume Drop & Tube Questions

Post by darkalone » Sun Nov 17, 2013 8:13 pm

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:

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