The Kalamazoo KEA amp now lives with my good friend Eric. It's become one of his favorite little amps to work with. We both think it's special sounding, very rich and clear. But alas, it still had some annoying issues.
This amp initially was a basket case. Doomed to the "part it out" pile. Missing speaker and all. I wanted to save it so luckily I found deep under the bench at Southside Guitars an old ceramic square magnet 10" that was shallow enough to fit in there. I replaced the field coil, with a 1k 10 watt resistor and yadda yadda, re-cap blah blah the usual.
In the end it became a lovely sounding amp. Impossible to make a buck off it so thankfully Eric wanted the thing.
The volume pot was scratchy so I replaced that. The schematic called for a 500k, but what was in there was actually a 1 meg. I used one of those to keep the integrity of the amp. You need to remove the power transformer to access the pot! Easy enough but it's one of those things where you realize what a genius Leo Fender was!
The pot was worn out but so was the .05 cap feeding it. That was leaking causing some scratchiness so I replaced that. He was stoked cause the pot was getting worse and worse, it only worked in certain positions.....
But it still had some rattle issues. Most were easy: microphonic old RCA 6V6 and very microphonic 6SJ7. Piece of cake!
But then I get that call..... something in the background sounds like a Fuzzface when it's out of batteries. The decay is like an amp that is biased way too cold.
I was praying it wasn't the speaker. We paid good money to have that dead old speaker rebuilt....
So first thing was I re-doweled all of the screw holes. Some were loose after 70 years. That helped. The chassis was vibrating.
But not 100% which is what we're shooting for.
So I figured let's lose that metal speaker grill. These amps likely weren't turned up to 10 back in the day. Those metal grills can cause issues. And we'll replace it with a boss looking vintage grill cloth. This amp sells for less than $500 on a good day so before you scream at me for changing that grill, I'll just say I DON"T CARE! And neither does Eric. This is an amp being used by a pro......
Anyway, that helped! Buy that decay was still bothersome. It didn't happen all of the time but it was annoying when it did.
So, next was more cabinet work. I mean, why didn't I think to glue that big ass crack in the baffle???
Done! Helped! Not perfect!!!!
So at this point I'm ready to throw in the towel. I sat down to lunch and had my Kabab Shack platter (Damn they are good there! 10 year customer!!!) when I had a thought:
On 70's Champs I always remove this one little capacitor that they added during the CBS era. It's a 330pf cap going from the control grid (pin 5) to the cathode (pin 8). This shunts some of the very high frequencies to ground, taming that sine wave if you will. When I worked for Budda we had a similar thing on the plates of the EL84 tubes to ground.
Some Champs I wound up putting it back in. Others not. Why replace it? On some Champs I got this ugly distortion, not unlike a Fuzzface with a dying battery.......
CBS sucked but they did a few things right.
So after lunch I did two things:
I added a 1 Meg resistor from the center tap of the volume pot to ground making it effectively 500K. I figured the schematic had a 500k for a reason. It's also not unusual to see values vary on amps this old. The pot was clearly original to the amp.
Then I also put a 100pf cap across that resistor.
And..... that did the trick! No more nasty distortion getting in the way of Eric's playing! And on top of that the amp just has a warmer tone. It didn't lose any volume or any bite for that matter, it just simply works better.
So now this "one foot in the grave, another on a banana peel" amp is ready to cut tracks. I didn't think I could like this amp more than I already did.
J
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