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PostPosted: Tue May 16, 2017 9:14 pm 
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Bottle Rocket

Joined: Tue May 16, 2017 8:53 pm
Posts: 3
Hey guys, I have had a Mitchell pro-100 combo for over a decade that I never liked the sound of. It was always noisy and grainy sounding. I finally decided to get back into playing and figured I would give the amp a fighting chance and recap it and replace the speaker. I am an experienced mechanic but limited in knowledge as far as electronic circuits go, so please go slow!

I have studied a few different schematics and pictures of open chassis, and I have noticed that someone‚Äč has clearly been inside of this thing before. What I don't know is the degree to which they knew what they were doing and why they did it.

What I assume is the filter circut has a bunch of mixed values, several of which don't concur with any specs on the schematic. For instance the brown paper Mallory is 70uf 350v, where the schematics and photos have suggested that it should be 60uf. Also one of the 3 30uf 500v caps has been replaced with a 22uf 450 volt... As well as the other cap on the preamp board.

However the most confusing thing for me is the extra 30uf 500v capacitor coming off the ground leg of one of the caps to the power switch. It doesn't exist on any schematics I've read or in pictures I've seen. What's the deal? Some cool mod, or lazy fix for dying filter caps? Should I just delete it, or replace it? Thanks for any advice you can offer.

I will include pictures soon, I can't see how to upload unhosted images.


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PostPosted: Tue May 16, 2017 10:12 pm 
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Bottle Rocket

Joined: Tue May 16, 2017 8:53 pm
Posts: 3
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Here are the pictures


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PostPosted: Fri May 19, 2017 5:35 pm 
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Bottle Rocket

Joined: Tue May 16, 2017 8:53 pm
Posts: 3
Just to follow up:
I figured it all out and my dad and I got the capacitors replaced, and cleaned up a bit in there. At first, it was hissing, spitting, and cutting out when you touched the master volume knob. My bad, because I let the amp sit for years and didn't fire it back up before working on it because I didn't want to worry about discharging it.
I replaced all of the pots that don't have a pull switch built into them, even though the two that do could use replacing... And MAN, does it ever sound better. It sounds so good in fact that I am likely going to let the authentic Mark IIB that I just acquired go. It's not quite fair to compare the two because from all appearances, the mark II is untouched inside. I am glad I was able to try this first on such a good candidate, because I would never subject the mark II to the learning curve! Here are some pictures of after:


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