Mesa Boogie Mark IIB Recap

Since the previous post about Caps and old Mesa maintenance was a success, here's another one, about a new amp!

The newest amp addition to the GUP Tech collection is a 1982 Mesa Boogie Mark IIB, 100W with Reverb, HR for the connoisseur. 

The amp was in pretty bad shape, no sound, missing tubes, broken speaker. It was a case of an all original amp, without any maintenance of any sort, unless an adjustable bias added (I don't like that). 

Again, a little reminder about capacitors and the need to replace yours on an old amp :

We've all heard about bad "Caps" before but what's the problem here exactly ? Bigger capacitors in tube amps are made with paper-oil-etc, and they will start to leak after a couple of years/hours of use. How many exactly, we can't be sure, but some state 10 000 hours, some 30k.

So for a 1982 amp like this one (40 years at the time we're writing this article), it's worth having a look at them. Since capacitor are quite expensive parts (around 150-250$CAD total for a Mesa Boogie Mark II), you wouldn't want to change them for nothing, but I'm sure you don't want to blow your amp either...

The caps are the big blue cylinders inside the amp. Those we're still originals, with little leaks around them, I don't like that.

So after a couple of orders on the internet and a some weeks, here we are, replacing them. Service inside those old units are easier than in the newest Mark IV. 

The power board is easy to unmount and access the connections underneath. Those caps are the easiest to replace. I also took the time to remove the adjustable bias circuit mod and tweaked a stock setup with a fixed bias.

Another cap needs to be replace on the preamp board :

This is not an easy one, you'd have to remove the whole board to access the connections I usually only solder the pins onto the original one.

All the tubes were bad or not very "new" so I replaced everything by new JJ stuff. I also removed the ALTEC speaker (broken cone) and installed a pretty awesome G12K100 speaker from Celestion. Note the empty ground switch hole where the bias was fitted.

The Reverb is fully functionnal, everything else is good after a good cleanup. It's not your typical IIC+, but this one is pretty good with an EQ in the loop and a good boost. The clean channel is really incredible.

Have a nice one!

Guillaume