Teisco Checkmate 17 - a dangerous repair

An unusual amp came by the workshop, It was in dire need of service, and was actually incredibly dangerous as it arrived. Luckily no one was hurt by this well intentioned little amp, It let us know it was in distress by emitting the most horrendous squealing oscillation as soon as it powered up. Details of the danger to come.

Teisco Checkmate 17 as it arrived.

The Checkmate 17 is a single ended amp using 1 el84 as the power tube. A 6x4 as the rectifier, and 2 12AX7 preamp tubes. It features a cool little piezo reverb and a preamp bias modulating tremolo.

Checkmate 17 rear

Checkmate 17 inspection card

Checkmate 17 serial number. Made in Japan

Cool knobs

Okay now that we've had a look at the outside, lets check out the inside.

This is the thinnest amp chassis I have ever seen, I'm not sure how much money Teisco thought they would save by omitting a few inches of metal, but I do know it was a bad choice.

Chassis

Its not easy to see in this picture, but take a look at the power switch. now look behind the switch. Teisco had to cut out a hole in the chassis just to fit a power switch in, what sense does that make!?

Checkmate 17 internals

Oh boy, here we go!! I believe the fuse holder had been replaced. Although it was done with good intention, the chassis is so shallow, that the end of the power cord is contacting the chassis. This amp came with a 2 prong power cord, so there was a 50% chance of having 120V AC on the chassis!! Guess what else is connected to the chassis? the shield of your guitar cable, and also the bridge and strings of your guitar. This amp was ready to kill, and I'm glad it got into the shop before it hurt somebody.

Power cord shorted to chassis

Lamp holder needs to be replaced

These capacitors have got to go

So the first job was to replace the power cord with a 3 prong grounded cord, and to ground the chassis. Next that fuse holder needed to be replaced with one that could fit the shallow chassis.

New fuse holder with heat shrink and adequate distance from chassis

Now that the basic safety was there, it was time to power up the amp and see what else needed to be replaced.

All the high voltage filter capacitors needed to go, and most of the coupling capacitors needed to be replaced.

New filter caps

reflowed solder joints and some replaced capacitors

Also all the ground connections needed to be tightened, and the lamp replaced.

After all of this, the Checkmate 17 is ready to be enjoyed again.

It has a really nice edge of breakup tone.

Tone is hard to describe, but I would say this amp sounds woody, pleasant and kind of cozy. What the hell does that mean?? Hm... Its not very loud, would be a lovely living room amp. The spring reverb is not as lush as a fender, but it still sounds quite nice.

If you made it this far into the blog post, I thank you for sticking it out! Till next time!

Checkmate 17 ready to go!