Wednesday, December 11, 2013

Kalamazoo Model 1

Here is a gritty looking amp that is in my favorite power range, roughly 5 watts from a single EL-84 tube. This amp was in tatters and didn't work when it came in. Needed a re-cap, it hummed. Was missing some parts as well.
These amps are usually a bargain. They boast a 10" speaker and can cost as little as a modern GA-5 or new Champion from Fender.

The screen resitor was burnt, being it's 1/2 watt this is not unusual. It was also melting the anode wire on the output transformer.

You can see how the paint is discolored in the middle. I relaced it with a 3.3k 3 watt wirewound:
This baby will never burn out in a million years. A little excessive yes but I like things that are reilable.

Took out the old filter cap:
And replaced it with 2 axial caps:
These are silicon glued to the chassis. I used to not like this method but after having worked on amps that other folks did this on with no trouble for over 20 years decided it is okay.

Next replaced the missing 150 ohm cathode bias resistor with a 5 watter:
I put a 22 @50 volt cap across it for hum reduction and a better bass response. You can leave it out but I feel like the amp can stand improvement.

Last thing done was to lift the ground on one end and install 2 100 ohm resitors as a hum balance between the heaters and ground. A trick I learned on these from a really thankfully picky and pushy customer. Amp runs quiet now and PACKS A PUNCH!

Play loud, play well! Jef

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