Mark IVa reverb question

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McFriedy

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Hi all!

I'm the brand new owner of a Mk IVa that is beautiful condition. I've been scanning the posts for tips and ideas and everything I've read has really helped me feel comfortable with the amp as I take her through her paces.

One thing I've noticed is that, as I turn up the reverb, there is a noticeable buzz/noise. It's not there at zero, and becomes prominent as I pass 3, and begins to sound like an overdrive pedal is engaged at 10.

Is this normal for these amps? It's not a huge deal since I have some f/x I can run in the loop, but if there's a simple way to fix it, I'd love to know.

Thanks in advance!
 
I also just purchased a Mark IV head last week, and it has the exact same problem. I read somewhere on here that it might be a problem with the reverb tank. If that's the case, it would cost $40 plus whatever it costs to install it. I'm not sure if that's the issue though.
 
Some ideas...

Check and clean all the RCA cables and sockets
Check that it is the right tube or type. I think i read here it's meant to be a 12AT7 in V4 not a 12AX7 in a MK4A and check that the tube is good.
Check that the reverb tank cables are not reversed/in the the wrong sockets. The reverb sounds distorted if they are. I made that mistake once myself.

I also needed a 'reverb glitch fix' I was sent from Mesa for a similar issue (background distortion) with my MK3 but I'd assume that is fixed in a MK4
 
Thanks for the replies!

The amp is over at the practice space right now, so I'll check out your suggestions when I'm there tomorrow night. I do remember checking out the V4 valve, and I can confirm it's a 12AT7. All the tubes are Mesa branded, so I guess it's possible these are the original tubes(?).

The amp is serial #IV58xx, and the underside of the chassis is dated 12/92. For a 25 year old amp, should I just get a fresh set of tubes for her?

Thanks again!
 
If cleaning the RCA connections doesn't work, I'd recommend changing the 12AT7 in V4, as someone else already suggested. I bought a '91 Mark IVa last year and it had really old Mesa tubes, possibly originals.

Congrats on your purchase!
 
Well, I tried changing out tubes tonight and learned that it's not a tube problem for my amp.

I also learned something unexpected but important. I used to own a DC-3 head. When I bought it, I replaced all the tubes with a JJ retube kit. I could never get the amp to sound focused -- it was always a bit muddy. A lot of people kept talking about how the DC-3 was not supposed to sound muddy, which confused me further. Anyway, I tried one of those old 12AX7's in my Mark IV tonight, and to my surprise, it made my amp sound a bit muddy just like the DC-3! I did some further google searching tonight and came across several websites where people were complaining about how JJ tubes can sound dark and muddy. Now I'm wondering if I never truly heard what a DC-3 head is supposed to sound like. Too late now, as I've already sold it years ago, but it makes me wonder if my ignorance cost me the chance of enjoying that amp much more. Oh well, I have the Mark IV now that sounds wonderful, so I can't complain. I just feel a bit stupid for not being aware that the wrong 12AX7 tubes will make your amp sound like mud.
 
Thanks everyone!

I think I'll spring for a new set of tubes and go from there. The previous owner said he didn't replace them, and he's had it for a few years, so I guess it can't hurt!
 

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