Kalamazoo Amp Field Guide:

Reverb 12 Chassis Removal Mod

DISCLAIMER:

Tube amplifiers contain potentially lethal, high voltages even after they are unplugged, that may cause personal injury or death. Do not attempt to repair, modify, or work on any amplifier unless you are absolutely certain you know what you are doing.

NO GUARANTEE

These mods are all things I have tried, someone I know has tried, or are recommended by people who work on amplifiers for a living. Nevertheless, if you try any of these, you assume all responsibility for anything that happens, whether the amp explodes, you get zapped, or the amp suddenly increases in value because everyone falls in love with it. The glory, the pain, whatever, they're all yours. If you can't live with that, don't mess with the amp!

Sorry - no photos yet!

What you'll need:

The single most important mod you can make to the Reverb 12 is making the chassis easier to remove and replace without scraping the faceplate up.

Remove the tubes to be safe. They pull straight out; do not twist them! Note where the two larger ones (EL84/6BQ5) go. Put the tubes somewhere you won't step on them, knock them off, drop things on them, etc.

Unclip the wires from the speaker, and disconnect the reverb cables from either the reverb unit or the chassis (I prefer the latter). If you don't do this, you may break something.

Next, you'll need to remove the chassis. This requires removing the upper back panel first (four phillips head screws). Then, there should be four 1/4" bolts securing the chassis to the cabinet. With the chassis unplugged from the wall, turn the cabinet upside down, so that the handle side is down. The chassis bolts will be on the sides. Remove all four with a 1/4" nut driver, screw driver or wrench. Instead of hex nuts, Gibson used the spring steel nuts that clip on to the chassis, so you shouldn't have to worry about the nuts; they stay in place.

Now turn the cabinet right side up. From the back, pull the chassis straight out until it stops. Now pull the back of the chassis up, gently pulling the chassis out toward the back as well. You may have to wiggle it a bit.

Put the chassis aside. Lay the cabinet on its front. Under the top of the cab, right beneath the handle, you will find four bolts. These are what the chassis hung up on. Remove two of the nuts from either end of the handle, from inside the cab with a 5/16" nut driver or wrench. (A set of nut drivers makes amp work a lot easier!) Hold a nut next to one of the bolts and note how much of the bolt sticks up past the nut; it should be about 1/4" to 3/8". If it's less than that, adjust accordingly when cutting the bolts. Remove the clip that holds the handle (pull from outside the cab). You may have to wiggle this a bit; the bolts fit snugly in their holes. [This will drop a bit of sawdust into the cab; vacuum this out after you are finished wit cutting down the bolts. Otherwise the sawdust may shorten the life of your speaker or affect the sound.]

These bolts are attached to the clip; do not try to remove them from the clip!

With a bolt cutter (some wire strippers include these) or a hack saw, cut off about 1/4" of the bolts you removed. Don't take off too much! With a metal file or wire brush, clean up the ends until the nuts go back on and off easily, and there are no sharp edges on the bolts to catch fingers or wires and components when removing or replacing the chassis. Replace the clip and reattach the nuts. Snug them down good, but don't over-tighten them. Over-tightening will break the bolts off the clip.

Repeat on the bolts at the other end of the handle.

With the cab still laying down, remove any sawdust that fell into it. If the amp has been gathering dust or cobwebs, go ahead and clean it thoroughly while it's apart!

Stand the cabinet right side up. Insert the chassis from the rear; it should now slide straight forward with no interference from the bolts. If you didn't cut enough off, you'll have to repeat most of the steps until this works, but I had no trouble eyeballing it and getting it right the first time, and I'm no machinist!

After doing any other work you wish to do while inside the amp (cap jobs, three wire power cord, etc.) reassemble everything. Bolt the chassis in place, reconnect the reverb cables and speaker wires, and reinsert the tubes. Replace the rear panel, and you are done!

Last updated: 14 September 2005

Copyright 2002 Miles O'Neal, Austin, TX. All rights reserved.

Miles O'Neal <roadkills.r.us@XYZZY.gmail.com> [remove the "XYZZY." to make things work!] c/o RNN / 1705 Oak Forest Dr / Round Rock, TX / 78681-1514