This is one of those clunkers-turned-golden stories. After the mods ive done, this is NOW my favorite amp (so far!).

This is the 2nd hardest to come across to Kalamazoo amps on ebay, next to the Bass 50. Models One and Two, and even the Bass 30 are easy to find, or come up in listings often enough.  Its tube complement can be compared to that of a Vox AC15 (12AX7 preamp tubes, and two EL84 power tubes).  Its been described to sound close to a Fender Princeton. This had a tremolo and reverb (obviously), thats footswitchable. The only other Kalamazoo amp that had an extra feature is the Model Two (tremolo). The rest have the rudimentary and simple Volume (or LOUDNESS) and Tone, or Volume and Treble and Bass.

Most of the mods that follow are based on the recommendation by Miles O’Neal at his site Kalamazoo Amp Field Guide. A Highly recommended site for all things Kalamazoo, to which we are grateful for.

The purchase:
Ebay is a great source for used, second-hand and vintage equipment that may otherwise not have seen the light of day, or the world’s exposure. Suddenly sellers have the whole world to sell to, and buyers now have access to remote far flung areas they cant reach or get to. I wont talk about how it has spawned unrealistic prices for what is usually less than a tenth of its value on most items. Instead i will talk about how there are still a lot of GREAT values to be had, if you know what to look for, and what to do with them, coupled with a certain amount of bravery (or in our case, foolishness!).

The seller described the amp as:

This Kalamazoo Reverb 12 amplifier is in good cosmetic condition but needs work. When turned on it either makes no sound or a very weak sputtering sound. I have changed the tubes so they are not the problem. I can see a number of new orange drop caps on the chassis so it looks like someone has tried to work on the amp. The amplifier has reverb,tremolo ( the pedal is included) and a 12″ speaker. I am sure this is a cool sounding little amp when working properly and will be worth the time it takes to fix. Shipping will be by FedEx ground. Figure 30 pounds from 23505.Use the FedEx website to figure shipping. The eBay calculator always show a shipping cost that is higher than it should be. I will not ship overseas … OVERSEAS BIDDERS PLEASE DO NOT BID.

took a chance, and I won it. Cheap! Within a week, it arrived.

FIRST LOOK: Outside
The seller packed it well, with NO annoying and messy peanuts (sellers, take note!). It arrived with no noticeable shipping damages. The tubes were in a separate box (good job!). What i saw inside was a surprise.
The amp was very clean! Usually amps this old have accumulated dirt, grime, dust, dried spills, and they usually are not easy to clean on those rough hide tolex covers. Colored black doesnt help, as it exposes those hardened dust between the light ridged texture of the tolex. This amp only had slight signs of this on top – the front sides and back look darker (less dust) than the top. Its like this amp had been stored with a cover for a while not long after it was bought.
It does show rust on the metal corners and on the handle ends. The front chassis was a bit dusty, and the knobs had the typical dirt on the sides from dirty hands. Its gonna get soaked and brushed clean.
The handle itself hasn’t had much wear on it, proof it hasnt been lugged and taken around much.
The grill cloth didnt have any stains, or has not been changed . Its the original cloth – its the same as the ones in my 2 Kalamazoo Bass 50s, and Models One and Two. The cloth had been slightly pushed in, as on an angle you see the round outline of the 10″ speaker circumference.
There were maybe 2 visible edge tears the size of a quick release tylenol pill, but no big rips. The corners are sharp, and the bottom shows no scuffs. Even the 4 rubber feet are still intact.

Second Look: Inside
To get to the chassis, The top back panel had to be removed first by removing 5 black screws. There were considerable rust on 3 of them, and one corner had already been stripped. Not unusual for an older amp, but the other 5 Kalamazoo amps ive worked on didnt have this much rust on them (or at all).
4 screws from the underside of the chassis needed to be taken out to slide out the chassis itself. It wasnt an easy slide out. The amp handle had screws sticking out from the underside that prevented a smooth pull – the chassis had to be lifted up to get it past the long screws.

Inside there were 3 electrolytic capacitors (1x47uF, and 2x22uF rated 450V) that stood out from the rest. A good start, though sloppy in execution. They were floating, held up by its long leads. Some cobwebs, usual dust, and what looks liks some odd dried out spills of some sort (not sure where it came from). The rest of the capacitors were sprague orange drops. The seller described it as having some orange drops replaced. I couldnt tell which ones, as they ALL were orange drops, and were all equally a bit dusty. There were still some non-electrolytic polarized caps that had not been replaced.
It still had the 2 prong cord (about 12 feet long!), and it was supple and firm, not dried out or brittle. The Footswitch was present! There was sadly NO schematic found. Important since this will easily tell me what version it was (theres at least 2). Now i have to compare the component placements with whats online.
The tubes that came with it are not original (theyre usually CMI branded), though they seem old stock tubes. 1 Fender branded 12AX7 made in the USA (most likely a westinghouse), a raytheon (made in japan), and an RCA. The EL84 tubes were magnavox brands, 1 made in italy, the other made in austria.
Though described as 12″, the 10″ speaker is not original and of unknown brand. It had an unusual square ceramic magnet (signifiying it may have been from the early 60s). There were some numbers on it, but it didn’t match any of the speaker codes found online. When it was taken off, it weighed very lightly, compared to, say a Jensen C10Q. The cone was intact and clean.
The reverb tank is about the size of the amp’s inner width, and had 2 spring in it.

PLUGGING IN!
True to its description, it sounded weak and sputtering! It’s hum and hiss was louder that the actual sound. Turning up the reverb only made it squeal. The Treble and Bass knobs had little effect. Connecting the footswitch DID turn on the tremolo, but it was spotty and intermittent.

THE MODS

SPEAKER CHANGE (and correcting the weak sound)
At first i thought the speaker was the problem. The description said the tubes are good (they were), but did not mention if they did anything to the speaker. First reaction (as described earlier), was that the speaker was very light. Even the CTS speakers from Model One Or Model Two are heftier. I swapped with it a MUCH heavier one, an oxford speaker (circa early 80s), thats similar in construction as a Jensen C10N, about 50 to 60 watts rated. The reverb 12 puts out about 10 to 12 watts. My aim was a better speaker than what was in it, not necessarily geared towards , say, an earlier breakup, or a certain sound. The higher wattage of the oxford speaker will tend to lean it towards a cleaner sound with a later breakup. At least, thats what i expected.
After a temporary connection, the sound was much fuller! And it sounded good too. I decided to leave the oxford speaker on, and reconnected the wires. Trying it again, the sound went back to being weak. It wasnt the speaker (but i kept it). I remembered NOT hooking up the reverb tank connections during the temporary connection. I took it off, and the full sound was back.

It was the reverb tank.

At that point i though of replacing it -i had 2 extra reverb tanks, one was the same size. 4 screws unhooked it off the cabinet floor. Once out, i noticed something wrong. The connection coming from the chassis was going to the OUT RCA jack of the tank, and the speaker connection was going to the IN RCA jack of the tank. I swapped those around, turned it on and got a full sound, with reverb!

So it wasnt any of the bad cap job, the speaker, or the reverb tank, it was just simple wrong connections. On to the rest of the mods!

TUBE CHANGES
The reverb is out of control (past 10 o’clock it feedbacks loudly). I decided to swap out the existing Japan Raytheon 12AX7 that feeds the reverb with a much lower gain preamp tube (a USA Tungsol 12AV7). Maxed out, hum feedback hum is gone. Later, after some cap job improvements, i was able to put in a slightly higher gain USA Ultron-brand 12AT7 with no feedback at max. I may try a 12AX7 again later.

MORE CAP CHANGES
There was still considerable hum and hiss and static going on. I had a new multi-cap can (4 values of 40/20/20/20 at 500V) ive been meaning to use on either Bass 50s, but this should make it a neater layout inside the chasses with just 1 ground to deal with. It can also free up the 3 floating caps for use on other areas.
I followed some of the recommendation from the Kalamazoo Amp Field Guide on where to place what caps – you can read more there. I didnt have some of the values recommended, but radioshack (gasp!) had some for relatively cheap. I coudnt wait for any online orders with this cap job.
This mod took the most time, done in between other mods, since it was mostly a juggle of what values sounded better for me, or which ones made the hum less.

NEW AND BETTER FOOTSWITCH (and removal of the useless PHONO/TAPE RCA INPUT jack)
There were 2 schools of thought i considered. One was to keep the same footswitch and just replace the very long 4 conductor gray to eliminate the intermittent reverb and tremolo. Or (after opening up the footswitch  and seeing its simplicity) MAKE a new one.

2 footswitches, a die-cast aluminum box, and a long 4 conductor cord can easily be put together. The problem was the connection TO the amp – it was an older 4 connection plug that can usually be found in older organs. But its not usual enough to appear in online stores that carry old stocks, or in salvage parts on ebay. So replacement of that is scratched – a NEW plug is needed. This means replacing the existing jack in the chassis, but with what, i havent a clue at that time.
I examined the connections to that jack in the chassis, and looked at the schematics online. Instead of 4, it outlined 3 connections (2 were combining) as it goes into the amp. This makes it easier, as i can use a STEREO 1/4 jack and stereo plugs, the same kind that most modern replacement footswitches use. Instead of MAKING a custom footswitch, i decided to use an already-made 2 button footswitch that i got for my Peavey Valveking 112. Making one is easy, but the time and cost is about the same as getting one ready to go. My main goal was to make the footswitch easily replaceable, in any case it gets lost or damaged.

I did make a mod in the footswitch – removed the LED connection out of the circuit, and hook up the conductor wires from it direct to the switches. It didn’t work with the LED leads in the circuit. It may work, and even light up the LEDs with another battery mod, but that just makes it more complicated, and may introduce foreign voltage into the amp once engaged. Keep it simple, stupid.

Connecting to the original reverb jack was simple – nothing needed to be desoldered and unhooked. All i did was piggyback off of it, and connected to it an open circuit stereo jack (again from Radioshack). The placement was crucial – i didnt feel like drilling a hole in the chassis, but still wanted to make it an easy access. I decided to remove the PHONO/TAPE INPUT RCA jack (and its resistor and wire connections), and put the reverb stereo jack there instead. It was a working input, but it was useless. I dont even use the second instrument input in the front. It was perfect – now the NEW footswitch can easily plug in without having to turn the amp over, or using a flashlight to find AND plug the reverb footswitch plug correctly, as is the case with the original. Try that in a dark stage.

Take note that this did NOT require removing and desoldering the reverb connections, nor did it require routing or drilling extra holes in the chassis or cabinet. You get to keep it relatively stock, and you save the original footswitch for posterity. The new footswitch is far more durable and can take the abuse from heavy leadfoots (being made of stamped metal). The original was made of molded RUBBER, with a fiberboard slide-in base. How it survived l those years is a wonder. This also makes footswitching easier with the wider space between switches. There was only a full inch between the switches on the original, on a 4 x 2 1/2 frame.

ADD MORE dBs! (make it a noticeably LOUDER)
On some older amps with  2 or more input jacks, using an empty plug on the second jack makes it louder. This is true for the reverb 12 (as is for the Bass 50, but not for the Model One and Two).
This was a no brainer – of course lets make it louder! But using an empty 1/4 plug into input 2 not only made it louder, it also induced some buzzing. The jacks were closed circuit, and plugging in to them opens a connection that makes the amp louder (which makes sense if you use more than one instrument in the amp, like a mic or as they used back then, a phonograph or a tape player). The trick was to sandwich a piece of stiff cardboard between those two poles that connect to separate them. The tension betwen the poles will keep it in place. No metal touching the tip or sleeve to induce unwanted buzz (in theory the metal parts may be acting like an antenna when an empty plug is used). Plugging an actual instrument still works.

SAFETY: 3-PRONG! (and moving the Power switch  and Fuse holder around)
This came later, as i did not have any toggle switch to use (another ratshack buy).
The Kalamazoo Amp Field Guide suggested to move the Power switch away from the tone controls as this induces hum, and use a 3 way  (On-Off-On) DPDT toggle switch, to have a standby in the same switch. I decided to use just a simple On/Off toggle switch. Per the site author himself, Miles O’Neal doesn’t feel this is necessary, though old-school thought strongly suggests making the standby switch necessary to prolong tube and amp life, as direct power On causes too much of an electrical shock to the tubes. The practice is to warm up the tubes for a good minute BEFORE turning on the rest of the amp. I dont practice a lot. 🙂 (OK – i may change this to one with a standby option later).

The toggle switch is now in its rightful place, where the fuse used to be on the front (next to the pilot lamp), and that left me thinking where to put the fuse holder.  I decided to “hide” it, away from kleptomaniacs and the occasional knob twister that cant refuse twisting the fuse holder open (and consequently either losing or taking the fuse, and sometimes the fuse cap too). It needed to still be accessible easily, but away from the misguided and curious. Taking out the 2-prong cord revealed the hole it came in thru the chassis. It was another perfect fit! With the top back panel on, its hidden – you have to turn the amp over and look behind the panel to see it, and its still within reach and easy fuse replacement.

The 2 prong AC outlet on the back has been effectively removed, for safety purposes.

And where does the 16-gauge 3-prong cord go thru now? I decided against using a 3 prong receptacle, the kind you see on computer power supplies (and in most modern amps nowadays). Its a perfect fit for where the AC outlet used to be. Its a decent way to replace the cord in case it gets worn or damaged, but the cord is also easy to pull off and lose. A permanent cord will NEVER get lost or forgotten when packing. Not good when your on stage and cant plug in to any electrical outlet. The new 3-prong cord now goes thru where the AC outlet used to be. I still need to put a rubber washer around it to prevent it from moving around the metal. At 16-gauge its thick enough to withstand cuts, but still a good idea to keep it stable. A knot inside prevent its from being tugged out.

EXTEND THAT EXTENSION SPEAKER
Plugging in a second speaker cabinet in the extension speaker jack cuts out the main speaker. Ive always wondered why this was so, spoiling whatever speaker you already have. It should be named Optional Speaker Output. So i decided to jumper 2 of the leads in the jack to keep the onboard speaker on with whatever speaker plugged in.
Then i thought about the other school of thought: Maybe some gitar cabs sound better on its own, and sometimes you just want to use another speaker for testing, recording, or just A/B’ing speakers. I ended up adding a small On/Off toggle switch to facilitate this option. Again, placement was key. I can either drill a hole thru the chassis on the underside, or somewhere easier to get to, like next to the output jack itself (where i have to drill not only thru the chassis, but also thru the top back panel). The less drilling the better. I ended up widening one of the holes that original held the AC outlet in place. This was right next to the power cord. Now if i have a speaker cab, i have the option to use it only, or in conjunction with the main speaker. The way it looks (and sounds), the speakers are in series, so theres no danger to the amp working harder (parallel speaker connection creates a lower resistance, making the amp work harder than it should. For a tube amp, this is dangerous and can lead to premature amp death. Or replacement of expensive output transformers. That’s wallet death).

EASIER CHASSIS ACCESS
This was outlined in the mods that Miles O’Neal wrote for the reverb 12. I didn’t fully understand it until i did the mod on my own, and reread it again.

The handle is fastened to the body (under metal covers) with the use of 4 screws, 2 on each end. These screws extend a good 1/2 inch down. When the chassis is removed, these extended screws prevent it from a smooth pull out. There was a cleaner way that Miles O’Neal described step by step. I Opted for the easy way – snipped them with a pair of metal cutters. I could have used my dremel for a much cleaner cut, but i was out of cut off wheels. After cutting them off, i taped over them with a thick adhesive tape. Theres still a bump, but nothing to fully impede an easier slide out. This beats having to removed the tubes, then the whole chassis, and finding a way to balance it on a table, when you can simple pull it out and start working on the components.

SUMMARY
Other things i did were more cosmetic – cleaned the front face with a damp rag, wiped down the tolex, and applied car dashboard polish to it. Also pulled off the knobs and found it had thick cobwebs behind 4 out of the 6 knobs. Cleaned them out, dipped them in hot soapy water, and scrubbed the remaining gunk out.

Some other things i may do:
– Remove the rust off the metal corners, and possibly spray it with clear rustoleum. Replacement is an option, but i’d like to keep it as stock as possible, with as little cost as possible.
– Replace the rusty back panel screws, maybe fill in some of the threaded screw holes.
– Reseat the grill cloth to make it more taut.
– Figure out a way to get reverb to the extension speaker. The reverb only works when the main speaker is on, nothing when the other speaker is on its own.
– Figure out star-grounding to try and reduce any other hum. With no guitar plugged in, Its quiet up til 11oclock on the Loudness knob. Past it it starts to have a mild hum.

This amp is made to RAWK! On the Volume/Loudness knob, the sound stays clean til 10o’clock, then starts to get gritty at 12o’clock, then starts to really breaks up at 2o’clock. Its the hounds of hell dimed – PURE TUBE DISTORTION! No pedal needed, unless you want to fuzz out more, or do more metal tunes, then a pedal can push it further. But nothing beats playing on simple direct guitar-amp connection.  Ive initially used a Danelectro Transparent Overdrive (used as a preamp) to try and boost the signal. I ended up liking the amps own tube overdriven sound, i ended up using the Dano in reverse, as a “cleanup” pedal – it dials in a cleaner sound with the volume and gain rolled back when its engaged, and when its off it kicks in the amps overdriven sound.  Ive discovered since that this is  one amp ive been able to play that cleans up well using the guitar’s own volume and tone controls, and now i dont use the Dano pedal at all.

The reverb is decent, not overly cavernous, but just right. The tremolo does its effect unexpectedly well. It does a simple soft modulation, and no option for a hard stuttering tremolo effect. Fine by me, because what it does is much better – on an overdriven sound the tremolo is more apparent at the DECAY of the note. You hear the effect more towards the end, instead of throughout the note. Its soft modulation makes it sound “more natural-sounding” too, like a singing voice vibrato when a note is held. I can still use my digital reverb and tremolo pedals, but if i have to use just the onboard effects, i’ll be fine.

This amp’s resurrection from near-death is a joy to think about. It makes it even sweeter that it cost well below what it normally goes for, and its cost of repair and improvement is even less than expected. Its playable again, ready for another 40 some odd years of playing. Im thinking this probably will be played more in the next 10 years than it did the past 40!

CHEERS!