Permanently removing reverb tank in a Mark IV A

[donniecrump]

I just bought a Mark IV-A and I want to completely remove the reverb tank. If I just unplug it will that work? Or do I need to do a little soldering and remove the RCA jacks as well (I would prefer this option). I am looking at this being a long term amp so some heavy modding would not be an issue.

I guess I should also add that the reverb is not working. Could this be why the gain is flat? The preamp tubes look to be good.

On a side note ... what kind of gain should I expect from an A version? Mine seems to have very little, sounding kinda like an old school Marshall, even on lead. Could just be a settings issue.

 

[dodger916]

You said the tubes "looked to be good", but that might not tell the whole story. Have you tried other tubes? Make sure they are all 12ax7s (ECC83) and not a lower gain 12xx7 (ECC8x) version (12AT, 12AU, etc..).

An "A" version should have gobs of gain.

 

[donniecrump]

I will check them out. The gain maxed out is not even close to what would be considered high gain. It has a unique preamp tube mix. I will pull them and write then down.

 

[donniecrump]

I have gotten the preamp tubes my MK4 pulled and here is the layout.

V1 = JJ ECC81
V2 = JJ ECC83S
V3 = Mesa 12AX7-A
V4 = Tung-Sol 12AX7
V5 = JJ ECC83S

I must say this looks like a custom tube kit. Should I just go ahead and get 5 Mesa SPAX7's? I am really leaning towards that just to see what happens.

I did get the gain to a better point. Although it still seems like I have a brittle sound.

Also .. does anyone know how to correctly remove the reverb tank? Can I just unplug it? Or do I need to perform some tinkering inside to close the circuit? Maybe join the 2 wires on the inside and remove the RCA style jacks?

Finally .. I got my Celestion V30 in today. I am going to pull the 200 watt Black Shadow beast out.

 

[dodger916]

The ECC81 is equal to a 12AT7, a lower-gain tube (70%?). Putting that in V1 will reduce the gain structure of the whole amp. Here's a quick test: Swap V1 and V5. You should notice an immediate gain increase. In V5 (phase inverter), an ECC81 can smooth the sound as it doesn't hit the power tubes as hard.

Given the tube selection, either the previous owner wanted a lower-gain amp or didn't understand the impact of tubes. Or, he just installed his least favorite tubes when he sold the amp...

Reverb tank: you can always call Mesa

 

[swbo101]

Just as a FYI, this is what I've been using in my Mark IV the past few years as far as pre-amp tubes;

V1 - Tung-Sol (RI)
V2 - JJ
V3 - JJ
V4 - Stock Mesa
V5 - Mullard (RI)

All are 12AX7 except for the V4 which is a 12AT7

 

[donniecrump]

Looks like that did the trick. Lots of gain now. Sounds awesome with the V30 instead of the 200 watt monster.

I did order the spax7 preamp tubes. One tube I loved in my last mark iv was winged c's. Sounded killer. Those are next.

I called about the reverb tank. They said to just unplug it and pull it out. Done.

Thanks for all the help.
Donnie

 

[donniecrump]

WooHoo! The Mesa SPAX7's are uber sweet. Completely smoothed out the entire amp. Before, everything sounded flat and a little harsh, and the channel's really did not have much of an identity.

But the main thing is my Mark IV now sounds "smooth". It is a little hard to describe.

One observation I did notice is the amp seems to really get happy after being on for around 15+ minutes. If you play it before then, it sounds all over the place.

Anyway one last post when I get my output tubes. Not sure what I am going to get.

 

[dodger916]

One observation I did notice is the amp seems to really get happy after being on for around 15+ minutes. If you play it before then, it sounds all over the place.

+1. I find the same thing with Mesa amps. It could also be the new SPAX-7 breaking in.