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MM 112RP 65


Posted on Friday, March 05, 2004 - 02:08 pm:   


Forgive me if the image didn't post correctly.

I got this 112RP 65 in a trade over ten years ago. I traded a Plush cabinet with four JBL 12's I bought for $150. I've pretty much been pluggin' in and playing it since I got it. The reverb tank was gone so I had a tech install a used one for $40. When I picked it up all he said was it wasn't a "true" tube amp in sort of demeaning tone. So my total investment was $190.

I'm just looking for as much feedback as I can get from others with the same amp (or who know about the amp). I have never changed the power tubes but it's missing the tube protection board on the back so I assume someone may have changed them at some point. It has two 6L6GC tubes, not marked with a brand name but have Made in USA molded into the plastic base. The chassis circuit board has a handwritten marking "Pat 5-11-79".

I like a clean sound sometimes and dirty other times so by using a Tube Works tube driver preamp along with a tube screamer I can get a variety of sounds. I experienced a mysterious "crackle" after about three hours of playing my last two sessions. It could be something simple or a bad omen. I took the front end effects out of the loop and still heard the noise. There didn't seem to be a major loss of power or anything. The amp does not hum or make other noises. I was going to start with simple stuff by going at the pots with tuner cleaner from the inside. I'd think a speaker problem would be an all the time noise not something that happens after it gets hot.

ANY info you can give me will be appreciated.
Posted on Sunday, March 07, 2004 - 05:00 am:   

Hey LastnoteJonny could you do me a favor? Would you check the number on your reverb tank and post it for me? I have the same amp as you and some one replaced the tank with one for a marshal.Man talk about tone, these amps never got the recognition they deserve.Thanks for the great pictures of your amp.
michael kaus
Posted on Sunday, March 07, 2004 - 07:49 am:   

You might have something as simple as dirty tubes sockets. These amp are getting old you know. A little Deoxit in the socket and move it in and out should do the trick. Also, a retensioning of the sockets themselves sometimes does wonders. Mike.
Posted on Monday, March 08, 2004 - 08:41 am:   

SS, I'll look for a number on the reverb tank but as you can see from my original post I had a used one installed coz the amp had no tank when I got it. I'm sure it was cannibalized from some other amp. If I got a MM tank it'd have been dumb luck.

I like the clean tone it has but the tech that put in the tank kinda snubbed it as "not a true tube amp." Using an external tube preamp I can easily switch sounds when the song dictates.

Thank my little sister for the digital pics and the photoshop composite.
lastnote johnny
Posted on Monday, March 08, 2004 - 08:52 am:   

I haven't done a thing except play the amp for over ten years. I'll clean all the pots, tube sockets, etc. and try your tip about retensioning the sockets. Thanks Mike.

You got any clue if these would be the original tubes from looking at them? I feel pretty sure this amp is supposed to have the 6L6GC's that are in it (also coz it's a '79). I was looking at Tesla (JJ) tubes, JAN Phillips or SED. Anyone who has the same amp have an opinion?
Posted on Monday, March 08, 2004 - 09:33 pm:   

In the Model chart on this site, it has for a 79 Music Man 112-65-rp-RP it is showing (2) 6CA7 tubes...?Mine is an 84 112-65-RP and it has the 6L6GC tubes. Might want to see if Steve or Michael might be able to guide you to the right ones.
Posted on Tuesday, March 09, 2004 - 08:26 am:   

In previous correspondence with Steve he said, "If you look at the schematic set, it indicates that the GD-1 circuit used 6CA7 tubes, while the GD-2 and GD-2a circuits used 6L6. If you could find one of these circuit numbers on the inside circuit board or otherwise identify the circuit from the schematics, then you would know for sure which tube was stock."

There are no numbers on the board I can find. Anyone able to tell from my pic of the circuit board? I can enlarge the pic if necessary. I've downloaded the schematics and will try to figure it out. I have a BA in graphic design not eletrical engineering so it's all new to me.

By the way SS, my reverb tank says "Accutronics, Geneva. Ill, Pat. #'s 2,982,819 and 3,106,610, 4FH2B1A."
Soul SercherU1
Posted on Tuesday, March 09, 2004 - 02:24 pm:   

Thanks the your number is the one I need. I will take mine apart to see if I can find what you need.
Posted on Tuesday, March 09, 2004 - 11:45 pm:   

I took mine apart to put 2 10 inch speakers in and clean it out. I checked the circut board and all I could find is a date 9/11/81. And it looks a lot different than yours in a lot of ways. on the side plate mine reads P/65 6-16 FP. You might post under a different topic on here for help also. Good luck, and thanks for your help on my proublem.
Posted on Wednesday, March 10, 2004 - 08:50 am:   

I'm cleaning everything as Mike suggested and will crank it up and see if it's any better. At least you got me to remove the reverb tank and clean it up as well. I'll worry about new power tubes when the time comes.

My bass player's been trying to get me into a solid state amp with guitar modeling built in. Screw that. I'll keep my MM. I just think this sucker needs some good ole tlc.
michael kaus
Posted on Friday, March 12, 2004 - 04:56 am:   

Good boy! These amps should be played, not looked at. SS amps have their place(they're great bass amps) but guitar should be run through a tube amp. Period. (Unless, you are a jazz phenom, which I I I I I am not). Let us know about the amp, we can try to help if that doesn't do it. Mike.
Posted on Wednesday, March 24, 2004 - 09:17 am:   

Hey Mike, I cleaned it all up all the way down to removing the knobs and scrubbing 30+ years of grime away. My gain pot was working up to 4 then wouldn't change until it hit 10. Now it has a smooth transition but still makes a bit of a jump between 8 and 9. I may still need to replace the pot but it's better than it was. I powered it up and shut off the lights and found my problem: one of the power tubes is glowing blue on one section, the other tube is glowing orange. I saw in another post that a blue glow is a bad thing so I'm retubing with 6L6GC's from JJ/Tesla...unless someone else has a better suggestion. I decided on those tubes after checking eurotubes and thetubestore. The biasing instructions in the forum seem pretty clear. I'm just not real sure what NOT to touch in there. Having had a gas grill blow me up a few years ago and spending a week in intensive care at a burn unit, I don't take too well to getting fried.