Carvin MTS 3200 Master Tube Series - Reverb and other ?s

[misterc57]

Just picked up one of these heads. It has an accutronics spring reverb mounted to the top of the head. If I turn the reverb up past 5, I get a lot of noise due to vibration.

The reverb is mounted with bushings. situation is far worse on the gain channel as that channel causes more vibration. Any suggestions other than not placing the head on the speaker cab?

I was also playing around with the preamp and reverb tubes. Swapping those out made no difference. One thing I did notice which I am not sure is a problem is that V1, the first 12ax7 makes a thumping noise if I tap on it. the other of the 5 12ax7 do not cause noise. I swapped that tube and had the same noise issue. So I am wondering if there could be an internal issue at V1 contributing to the noise.

If the reverb is turned down to zero, v1 will still make a thumping noise when tapped. However there is no vibration noise coming from the reverb unit.

Is this normal or could there be an issue at v1?

Thank you! Mark

[Prairie Dawg]

I'd pull out the tank and make sure that the springs are properly attached at all points. Once you've done that, you may want to make sure that your reverb driver tube is the correct one-people often replace them with the wrong ones.

As a precautionary measure you can secure the tank on top of a sheet of corrugated cardboard tie wrapped on before you slip it into the bag, and/or glue a strip of foam rubber down on top of the tank.

Once you've done that you can proceed to check your preamp tubes for microphonics by 'tunking' them. The old radio supply houses used to give away pencils with two erasers at 90 degree angles for this purpose but you can do as well with a pencil with one of those pink slipon erasers.

If the tube is microphonic it'll ring and tend to continue. A little thump is not a real problem.

[misterc57]

This reverb unit is in a metal housing (not a bag). I will take it out and inspect the inside as you suggested.

There are (5) 12AX7 and (4) 6L6 tubes in this amp. V1, V2, V3 are pre-amp, V4 is reverb, V5 is power inverter (I think).

Thanks again! Mark

[Krwkka]

Move the Tank

I have one of these amps and had the same problem. I tolerated it for a couple of days but it was just too bad so I moved the reverb tank to the front panel of the cab (as in Marshall heads) and the problem vanished!

Be careful not to get the cables to the tank pinched when you put the chassis back in!

[misterc57]

moving the tank ?

I am going to have to make a front panel because my head was modified to have a plexiglass front panel. I was hoping the guy I bought it from would find the original panel but that has not happened.

Do you have the input/output jacks facing up or down? The back panel is very snug fitting. Is that true of the front panel also?

Thanks, Mark

[Krwkka]

Yeah, that complicates the matter. I'll bet the plexi looks cool!

My jacks are facing downward.

I don't recall the panel being noticeably tight.

[misterc57]

picture with the plexi

picture attached.

[Krwkka]

Hmmm. I'm afraid I can't say I love the look... however, if you would spray the top part of the chassis a flat black, it might work.

I'm not too fond of the look of the stock panel either. I keep playing around with the thought of replacing mine with a nice piece of figured maple.

[misterc57]

Today I finally got around to building a front panel out of a nice piece of pine. Installed the tank on the front panel. Now my problem is a humming noise that comes from the reverb.

With both channel volume at zero, as I turn up the reverb pot the hum gets louder. At the zero position there is no hum.

I have the connectors to the tank facing up. I positioned the front panel upside down so the connectors face down, no difference. If I move the front panel out and rest it on top of the cabinet, there is no hum.

So I am guessing it has nothing to do with the reverb tube but the position of the tank.

The good news is that the original problem (noise from vibration) is gone.

Any suggestions??? Thank you. Mark

[Krwkka]

If the reverb return cable runs too close to the power transformer you'll get hum. Could that be it?

EDITED TO SAY:

I just reread your post. No hum when you move the tank away sounds to me like confirmation that you're picking up transformer hum on your return -- either the cable or the tank itself is too close.

[misterc57]

location of the return cable was the problem. can it be shielded?

You were correct.

I repositioned the tank so the return cable is farthest away it can be from the PS. I tucked the return cable between the OT and the side of the cab.

The hum is practically gone now.

I was wondering if the cable can be shielded somehow?

Thanks, Mark

[Krwkka]

The cable you have is shielded. I'm afraid that it would be very difficult if not impossible to eliminate all of the hum, but I would hope that the reverb is at least usable now.

How did the front panel that you made turn out? Did you put a finish on it?

[Gtr_tech]

Its not the cable that is picking up hum, its the reverb tank pickup coil. Its not shielded other than partially by the metal rev tank housing, so all you can do is keep that end of the tank away from EMI sources.

[Gtr_tech]

I did that with a Peavey VTM head. I used Lexan for better durability.

[misterc57]

works good and picture

Can't decide if I should put the logo on the front or leave it off.