Friday, May 24, 2013

Teisco Checkmate 60--A First Look

Busy times--too many distractions prevented me from posting about the vintage Teisco Checkmate 60 amplifier. But here it is, in all it's worn glory. I'll keep this post mostly a preview, and not include too much detail...

First off, two of the front-panel knobs are missing. It's easy to spot the "stunt knobs" in the photo. The front panel itself is very clean. The tolex is decent.

Here's the back. Sorry, these aren't glamor shots--not enough free time currently. But decent enough resolution, compared to any other web photos.

It's not perfect. Plenty of imperfections. A coating of mouse piss (or is it?) inside to clean up. Some rust, too. The handle is missing.

Let's be straight, right off. The one significant disappointment is the output transformer, which is non-original. More--MUCH more on this later.

But it works, as-is. EVERYTHING works--reverb, tremolo, both channels, all the switches. Even the replacement OT works. Again--more later. And it sounds GOOD.

Whaaa.... That's pretty nasty. Note that some of the crud has already been scraped off the chassis. Luckily, the underside "guts" of the chassis are pretty clean. The chassis itself has an unusual in-cut or inset corner (on right of the photo). On the inset are jacks for the reverb and tremolo footswitchs. The high corner steel panel in the inset is unusual, too--maybe the footswitch and cable tucked into the inset for storage. For some reason, the steel panel has been bent and will need attention.

No way! That's NOT an output transformer for a 60 watt pair of EL34s in push-pull configuration. Nope, it's only attached with one screw--it's too small to reach the second hole in the chassis. The original was definitely larger. But it does provide proof-of-functionality (again, more later). 

The residue around the OT is wax, probably from the current or the previous transformer, which was likely potted. Since the original is gone, it's the primary suspect.

By the time I'm writing this, I've made progress. This amp is COOL.


Here's a chart of the chassis, top side. The tubes and major components are labeled. There are four 12AX7, two 12AU7, and a 5AR4 rectifier. There are three multicaps, a reverb tank and the reverb driver transformer.

Power tubes? The Checkmate 60 uses a pair of 6CA7 tubes (EL34). I suspect this IS the original power tube complement. Other sources reference a pair of 6L6 tubes, but I offer as evidence a blurry enlargement from the '68 catalog:

While it incorrectly lists only one (two are required for 60 watts), it clearly does reference the 6CA7, which wouldn't be used in a guitar amp for anything but a power tube (there's also something X 2, but it's nearly illegible--might be a measurement, almost looks like "30cm"). The two power tubes are mounted on a small "daughter board" set into a rectangular hole in the chassis.

The back panel image is below. "Tremolo" and "Reverb" are footswitch jacks. The rest is self-evident. There's some weirdness with the speaker jack wiring, but I'll detail that in a later entry.

Incidentally, a historical Yen-to-USD online calculator indicates that 90,000 yen in 1968 equals $889.90 USD (or 687.98 EUR). Adjusted for inflation, that converts to a value in 2013 dollars of $5,946.25. For both the amplifier and the cabinet, of course. If purchased separately, the cabinet was 32,000 Y, about 35% of the total. You do the math...

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