Mark IIB Chasis Removal

[jnoel64]

This will likely sound lame, but here goes...

I am trying to remove the chasis from my Mark IIB so I can inspect and replace the preamp tubes. I noticed a ground wire inside one of the chasis screws on the top of the cabinet. Never saw anything like that before, lol. I am struggling to pull the chasis out. Wiggling makes some progress, but I am now wondering if that ground wire is hanging me up somewhere. Is there any special trick to pulling the chasis? Or is it more of just a giant exercise in patience? FWIW, already disconnected the speaker cable and reverb cables. I'm not a total noob, lol. I just want to be sure I don't cause any damage.

I have noticed markings on the chasis for each preamp tube. There are 2 that are marked 12AT7. One actually says AX7/AT7, so I assume that's a preference. The power tubes were STR 440s. Not sure when Mesa stopped offering those, but I recall them being the same as TAD 6L6 STRs. I have a couple old STR 415s I may have to put in there. Those are amazing sounding.

 

[sloanthebone]

I would like to know what that ground wire is for as I have it on my IIb also. I am building a head shell and would like to know if it’s needed. Anyway, it shouldn’t stop you from pulling the amp out. You do need to take the power tube out on the far right. Can’t think of anything else that would stop it as long as everything else is unplugged.

 

[user 41014]

Most of these cabs should have a conductive sheet on the underside of the top (like you would have to shield a pickguard) for the chassis to snuggle up against. If it is a sus-4 shock mount cab there is a wire on one of the mounts. It doesn't go to the chassis.

You can pull the chassis out tubes and all but after popping a STR-454 on a combo EVM-15L I yank the power tubes. And power tubes have doubled in price in very short order so the penalty is higher.

I keep a 12lb sledge and tire iron handy for the tight ones. You'd be surprised how quickly it loosens right up.

I suppose you could rocker it and lightly lift / pull it as another option. Get the power tubes out of the way and get a good grip on the tranny's. Hangups can be loose tolex on the back lip, the front plate hanging on the front grill, reverb/speaker cords and don't forget to unplug the fan.

 

[jnoel64]

Most of these cabs should have a conductive sheet on the underside of the top (like you would have to shield a pickguard) for the chassis to snuggle up against. If it is a sus-4 shock mount cab there is a wire on one of the mounts. It doesn't go to the chassis.

You can pull the chassis out tubes and all but after popping a STR-454 on a combo EVM-15L I yank the power tubes. And power tubes have doubled in price in very short order so the penalty is higher.

I keep a 12lb sledge and tire iron handy for the tight ones. You'd be surprised how quickly it loosens right up.

I suppose you could rocker it and lightly lift / pull it as another option. Get the power tubes out of the way and get a good grip on the tranny's. Hangups can be loose tolex on the back lip, the front plate hanging on the front grill, reverb/speaker cords and don't forget to unplug the fan.

Thank you for the tips. I had forgotten about the fan!

 

[woodbutcher65]

Use a THIN steel sheet or scraper knife blade and slide it around the chassis edge and you'll feel what's holding it back.
It's often just tolex rolled up in the gap between the chassis and the cabinet. Mesa's cabinets can be very tight sometimes,
with so little clearance that the tolex is enough to make installation and removal difficult.