Mark IIC+ with noisy pots

[es335td]

I have a Mark IIC+ 60 watt that was last over hauled at the Mesa Factory in 91. I have done little to it since then except change the tubes. It does not get a lot of use sits mostly I gig with my Twin but if I am playing an exceptional large venue I run them both through an AB and run the Boogie clean and use the lead channel for that extra kick. This config seems to deliver a pretty cool sound.
Anyway I set it up for this config last week and found that all the controls except the treble are super scratchy. The most offensive are the Volume 1,Master, and Middle. Do you think my preamp tubes are crapping out or do you think the pots need to be cleaned, resistors replaced, bad caps? I love this amp but it is unusable like this.
Any ideas.
Mark IIC+ SR #13838 with the EQ.
Thanks

 

[es335td]

Ok I can see you guys are looking at this post but no one seems to be answering. in the void of any useful advice I have decided to go ahead and replace the preamp tubes it couldn't hurt, right? So I took the head out and when I am removing the reverb cables I notice that they are on RCA type connections that seem to be after market? beside each of them are 1/4" jacks. I can not imagine that the original amp had RCA I would expect it had 1/4" do you think this is a mod someone did?
It has hand written on the head WB 12-84 so I am assuming that is the build date and the assembler, and it also has in large letters SRG 38 written on both sides, near the power cord it has the + as I would expect for the C= but it also has the WB hand written there as well. On the pother end of the back it has GM 4/91 hand written and I am assuming that was the tech that worked on it when it was overhauled in 91. I hand carried to the factory and had them ship it back to me in IL in a flight case I provided.

 

[es335td]

Ok still talking to myself,
I changed the tubes and the improvement is remarkable although the volume 1 is s till very scratchy. I am going to try cleaning the pot and if that does not work I will change it out unless someone has a better plan.
I would still like to know what this chicken scratch is all over the amp head section and the extra set of jacks in the center of the chassis. Any thoughts I know you guys are are out there.

 

[Allen]

Tube pins can pick up micro corrosion from the heating and cooling effect pulling in moisture.

I live by the ocean, and the salt air adds another component to the equation.

So, I clean the tube pins on my amps a couple of times a year.

Caig DeOxit Gold is an excellent product for this and it doesn't take much of it to clean the tube pins. It has a high flash point so it won't boil off with the high temps of your tubes. I spray a small amount on a cotton swatch and burnish the pre-amp tube pins.

You may also have some dirt in your pots. The wipers can also get micro corrosion on them. A couple of shots of the regular DeOxit and just working the pot will probably take care of it. You will have to take the chassis out of the cabinet to access the back sides of the pots. This is a good opportunity to look for swollen electrolytics and blow out any dust or bugs that have crawled in there. Giving the amp a good visual inspection can head off problems before they happen.

Hope this helps.

Allen

 

[es335td]

Thanks Allan
I replaced the tubes, cleaned the pots but it is still a little scratchy on volume 1 so I will hit it again with the cleaner. Since the tubes are now new I would not expect any oxidation besides I live in IL so not much salt air here. Thanks for the tips it is sounding better and I found what the SRG 38 means. still not sure about the 1/4" jacks any idea on that. also mine seems to have a WB instead of MB kind of strange could be an M but really looks like a W I am sure he was in hurry that day. Dec of 84 it is marked and he signed the back next to the + as well.

 

[Allen]

The jacks in the middle of the chassis are the pre-amp send/power-amp return and the reverb/graphic pedal jack (single stereo jack). Do you have the Reverb/Graphic stomp box?

You may want to read the original Mk2C manual that Mesa Boogie included with the amps. I think this document is somewhere here on the board in a sticky. Have a look around. It actually is a worthwhile read.

 

[Allen]

Also, I just remembered that the effects send/return jacks can get intermittent contact and cause issues.

You can carefully clean those contacts with some DeOxit on a cotton swab, or just spray some cleaner on cable jack and cycle it through the jacks, cleaning off any deposits from the cable jack.

Been a while since I have thought of this stuff, but that was a common issue as I recall.