Reconditioning My Kalamazoo Model 2

The Kalamazoo Model 1 & 2 amps were inexpensive practice amps produced by Gibson in the mid 60's.  They make wonderful harmonica amps. For background, schematics, mods and more see:

This is what I started with. Not too bad for $65 off eBay. The ad said "doesn't power up", but when I first plugged it in, everything except tremolo worked. And the sound was AMAZING with harp through both my Green Bullet and BluesBlaster microphones.

Only later was I able to repeat the no-power-up condition. (Bad AC cord/plug)

Lets take a closer look. As you can see this amp has some mileage. Some of the screen printing has been worn down to the point it is almost completely gone.  Hmm... Seems the Tolex is flapping in the wind a bit, revealing...

A bit hard to see in this picture, the particle board cabinet had seen better days. A 1/4 inch 'valley' of particle board was gone along the top edge on both the left and right sides of the amp. Past repairs left a bit to be desired.

A peek in the back and things get more interesting. The upper back cover plate is missing. But more importantly, what is the deal with those filter caps?

They look like some sort of strange electronic trapeze act. That won't do. I never work without a net.

Why bother with a good connection? Just wrap those speaker wires around the spade lugs! That baffle board doesn't quite look right either. In reality the baffle board was far worse than it looked.

So what to do? I want the amp to be 100% functional and to hold up to another few decades of abuse. Certainly the electronic problems need to be fixed. I thought of making an all new cabinet as well. Maybe something snazzy in a nice tweed outfit. But this amp earned its battle scars honestly, so who was I to try to put a pretty face on an old warrior? So on to the repairs...

This looks a lot better to me. A bit of hot glue to hold 'em in place, some nice new wires to hook 'em up, and the filter caps are now far less likely to be participants in some sort of inadvertent fireworks display.*

As I mentioned, the tremolo wasn't working, the culprit being a bad 10uF electrolytic cap. The replacement is the little blue fellow nestled 'long side the resistor below.

For all you safety freaks, I updated the power cord with a 3-wire grounded line, and rewired the switch circuit accordingly.

A bigger job was repairing the damaged edges and corners. After removing the worst of it, I used "Minwax High Performance Wood Hardener" to firm up the crumbly 40-year-old particle board. I filled the afore-mentioned 1/4" groove with hot glue to hold it all together, leaving a bit of room at the top for filler.

Next, I rebuilt the damaged edges and corners using "Minwax High Performance Wood Filler". Learn from my mistake and save yourself a few bucks. Minwax High Performance Wood Filler is nothing more than BONDO.  Then a quick coat of flat black paint over the repaired area. 

I have to make a confession here. I'm not sure if it was out of laziness, or a keen sense of style, but I did not strive to make the repaired areas perfect. My thought -- or rationalization; you choose -- was that they should appear in keeping with the condition of the rest of the amp.

In this pic and the next you can see a shiny new #1 input jack. The normally closed switch in the original jack, which mutes the input when nothing is plugged in, had given up the ghost.

Here we are with the Tolex glued down. Doesn't look all that bad. I've ordered some gaffers tape to do the finishing touches. Gaffer's Tape is a flat black, high-strength version of duct tape. It should do the trick to protect those edges and corners while blending in as well as can be expected with the old Tolex.

To say the speaker baffle wasn't doing well is an understatement. Seems the speaker, the cabinet, and the grill cloth were the only things holding it together. Sort of like the rust on Greg Brady's car. Not as bad as below, but pretty bad. I finished it off trying to salvage the original glued-on grill cloth.

Note the 'crossbar'. This is one of two strange things about the baffle board design. The second is that when mounted in the amp, the bottom of the speaker was below the cabinet opening. I suspect both 'features' were intended to reinforce the baffle board due to the weakness of particle board.

P.S. If you want to reuse grill cloth, my advice is don't wash it. The original grill cloth from this amp now fits a small transistor radio. I took the economical, rather than the authentic, approach and ordered some generic black grill cloth for replacement.

Here's my nifty cardboard template for a new baffle board. I've deleted the crossbar and moved the speaker up a bit so as not to block so much of it with the cabinet. Ironically, the cardboard mock-up probably would lend more support to the speaker than the old baffle board. And yes, those are indeed spade connectors on the speaker wires.

Here's my new baffle board made from the above template. It is 1/2 plywood, 1/16 thicker than the original particle board. 

The speaker screws are rather unique. They have two threads of different size, and of reverse direction. The coarse backwards thread screws into the baffle board. The normal thread is for attaching the speakers with nuts.

The new grill cloth was surprisingly see-through. To get an opaque look required two layers.  I simply wrapped it around and stapled it in place. Gluing wouldn't have worked due to the dual layers.

No well-meaning project can be completed without running into at least one unexpected problem. In my case, the extra 1/16 of the new plywood baffle, along with the dual layers of grill cloth, was enough extra thickness to keep me from being able to screw the nuts on the baffle mounting screws. I cut away grill cloth around the ends of the screws and drilled countersink holes on the back of the baffle board to work around the problem.

My new cover is 1/4 plywood, covered with gaffer's tape. Since taking this picture I've smoothed the area around the screw, but I'm too lazy to take another picture.


And the final (??) touch, protecting the repaired edges with gaffer's tape. Not perfect, but blends in well enough for my "keep the vintage character of the amp" approach.

This picture was taken before installing the new rear cover and taping the reworked corners & edges. But it looks good so I'll go with it!

* Postscript: While working on the rear cover, the hot-glued filter caps came loose. I re-attached them with two part epoxy.

I should take a few pictures of the actual final product, but I think I'd rather plug in and play!

I'd be happy to hear your feedback etc!

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