Mark IIC+ help

[MesaGravy]

Hi all. So this weekend, I rejoined the Mesa family, after a long stint with EL34 british amps. I bought an absolutely mint, original 60w Mark IIC+ combo, blond/black, with EQ and reverb. (I actually traded a guitar for it). It is one of the most amazing amps ever, but like all of the mark series, it takes some serious time with that EQ to sound good! I actually liked it so much that I also picked up an old 2 channel dual rec, but thats a story for another day

Anyway, I have a problem with the iic+. When you play an extremely low frequency note, as the low frequencies are ringing out, the amp starts to crackle a little bit. It doesn't happen until after the note is played and ringing, and it only happens with the absolute lowest frequencies, like open E when the bass is boosted and deep switches pulled. I don't think its the speaker, as the original note sounds heavy and clear, but with a crackle following afterward. I replaced all of the tubes in the amp with brand new mesa's, and made sure all of the connections were well seated in the speaker connectors and to the reverb tank. The reverb and presence are off, so I don't think its a reverb problem. None of the knobs crackle when turned, so I don't think its a scratchy pot or loose input jack.

My hypothesis is that the low frequencies are rattling some internal component in the amp and causing the crackle. I plugged in my 2x12 cab, and when the cab is pointed away from the combo, there is no crackle, but if you put the speakers right up against the back of the combo, the crackle returns!

Tomorrow, I plan to clean the tube sockets with contact cleaner, but I don't think this will solve the problem.

My questions are these:
#1 anyone have anything simliar to this happen to them with a mesa combo
#2 anyone know any reliable techs in chicago?
#3 should I send this thing back to Mike B to have it gone over? How much do you think that would run me?

Thanks for your help!

 

[dodger916]

If the filter capacitors are original, it may be time to replace them. I've heard from others that they affect the low frequecies most. Even if they are not to blame, it's a good idea to replace them after 10 -15 years, especially if you love the amp.

Fret not: someone with real knowledge will chime in!

 

[JOEY B.]

I had the exact same problem. My issue ended up being a loose ground braid that connects to the rear of the pots. I would send the chassis to Mike for a tune up. The peace of mind is well worth whatever it costs. 8)

 

[acorkos]

you or a tech would have to spend time with the chassis open and the amp running, poking around with a wooden stick, looking for a faulty solder joint.

 

[Paul Secondino]

The comment about the ground on the pots is a good one. It could easily be a tone pot or volume/ gain pot . Clean out all the pots thoroughly and test each one to see if it brings out more of the crackling problem.

 

[JOEY B.]

The comment about the ground on the pots is a good one. It could easily be a tone pot or volume/ gain pot . Clean out all the pots thoroughly and test each one to see if it brings out more of the crackling problem.

My problem would show itself when the "Pull Shift" on the bass pot was activated. The combo speaker would make the problem much more apparent than an extension cab at loud volumes placed nearby, but it still would occur. Good luck on your quest.

 

[MesaGravy]

Thanks for all of your help and suggestions. Joey, I have the EXACT same problem. I took the amp to a well respected local tech, Tim Schroeder, here in Chicago to see if he could help me pinpoint the cause of my problem before taking the step of shipping it back to Mike B. I figured if it were an easy fix, he would be able to do it quickly and if not, I wouldn't be out more than a hundred bucks or so and I'd end up shipping it back to Mesa anyway. I'll keep you all posted as to the outcome.

PS. I ended up trading the Rectifier for a red stripe Mark III to keep me busy in the meantime. Its a sweet amp in its own right!