Please tell me what current amp this TEISCO CHECKMATE 20 is closest to....

[aaron]

Hi guys!

First off, I don't have pinterest so I can't post the schematic. Sorry 'bout that! But if you google "TEISCO CHECKMATE 20 schematic", it's right there.

I have an opportunity to buy this amp for around $100. the owner says he doesn't know if it works or not. I'm trying to get pictures of the trannies to see if they're in good shape. So, before I buy it, if it was in pristine shape, what kind of amp do you think it would sound like?

Is the amp close enough to another amp that exists that with a few mods, I could have a great amp?

I despise Tremolo, and would use Reverb sparingly, so I would consider deleting those circuits. Would you suggest a higher gain amp using the 12AX7's for more gain stages?

Some things I (think) I have surmised:

1. It has a neg. feedback loop
2. It's push/pull
3. The 7189A tubes are VERY EXPENSIVE
4. It's running over 400V at the tubes

Why do think the company is using such a high voltage?

I'd love to hear your ideas on what to do here.

[olddawg]

Sounds like a great deal if it is close to operating. You can mod it to use EL84s. I've never done it but there are people on this board that have. The amp was a cheap alternative to a Fender Deluxe Reverb at the time. A little less power. Not a lot of gain in this amp but will probably like an OD pedal.

[aaron]

thanks for the info

Hmmmm, a Fender Deluxe Reverb...

I'm not sure it's right for me...

For example, someone near me is selling a Fender Hot rod Deville 4x10 pretty cheap. I'm thinking to myself, there's no way I could ever crank it up and enjoy it...I live in an apartment in a good neighborhood.

I probably couldn't crank the Teisco up either....

[Mick Bailey]

When you refer to cranking the amp I assume you're not after a clean sound, and this is a fairly clean amp unless you turn it up and then you'll get more crunch. Think of the clean sound you'd get with maybe a Blues Jr, or even a Pro Jr. The output tubes are fine running at 400v and this gives a little more clean headroom than a regular EL84, though there are amps that run high voltages on EL84s - Traynor, Marshall, Mesa and many others.

The amp is really nice if your playing style fits in with what it offers, otherwise it may be too far off to easily modify. If you're looking for a high-gain amp with master volume this is not the one, unless you heavily modify it out of recognition.

You don't say what you're looking for in an amp, or what genre you're mainly interested in. This amp is more Chet Atkins than Mick Thomson.

[aaron]

thanks Mick.

clean sound is fine, just I can't "afford" to have the neighbors call the police while I wait to get the "crunch zone". That's also what I meant with my Fender H.R. Deville comment. I'd prefer to get to tube distortion before the paint peels off the walls....

Another thing is that I don't need 400V pushing a really strong tube for the sake of more headroom. I also don't know yet if the 7189A's are in good shape or not...at around $50/each, it's not worth it for me.....so, yeah, some mods will probably be in order.

[J M Fahey]

If the amp is already "almost" what you want and needs only very little tweaking, then go ahead.
Don´t try to turn it into something it is not, specially if to begin with you are not interested in almost 50% of the knobs it has (reverb and tremolo) and on the contrary want something it definitely does not have (high gain/preamp distortion).
You will spend tons of money and time to get a half baked thing.
IF that Hot Rod Deville (or any other) suits you as-is, go for it instead.
If your fingers itch to build something, (rebuilding your Teisco amounts practically to that), make an appartment/neighbour friendly AX84 amp ... the high gain one if you wish.

[Mick Bailey]

The amp can use the Sovtek EL84M, but there are some differences in the way the pins are internally connected and the amp may need modification to the socket connections. The 7189A has pins 1,2 & 6,9 internally connected inside the tube. Other than that the EL84M will handle the voltage just fine.

Just bear in mind that an amp of this age will have problems and is highly likely to need a full recap. A picture of the trannies won't tell you if they're any good and the only real way of knowing is to hear the amp working.

When it comes down to pushing an amp, I have a little 1W amp that when cranked annoys my wife watching TV two rooms away in a house with solid stone walls.

[aaron]

Yeah, I'm expecting a full recap and other parts...I like getting my hands dirty!

Is there any way to know what the power transformer voltages should be just by looking at the schematic? (No, it's not written down).

Well as long as I've opened up this can of worms, can anybody tell me from the schematic:

1. The PT is marked "PT-20", and the ouput transformer is marked "OPT-25"...what do the numbers stand for (watts?)?
2. The resistor right after the diode recitifier is marked "5K6P1". The 1 is a subscript. So I assume 5K stands for the resistor value, but what does the "6P1" mean?
3. Someone else on this forum seemed to say that there is a voltage doubler circuit. I'm no expert, but I don't think so...who's right?
4. Some of the resistors say "1/2" after the value...I assume that means it needs a 1/2 watt resistor, right? What do the other resistor watt values have to be?
5. The diodes are marked "5W-05C"...if needed, what would I replace them with?

Thanks for the help!

[J M Fahey]

The Million Dollar Question: have you or have you not bought it?
Be aware that this is not a "$100 amp" but you will have to invest money and effort .

You may think that this 20W amp will be less loud/annoying than the HRD ... think again.
This one can deliver any crunch at all only by overdriving it in full, the HRD has a dirty channel and a Master volume, you can set it real quiet if you wish ... you can not do that with the Teisco.

[J M Fahey]

Is there any way to know what the power transformer voltages should be just by looking at the schematic? (No, it's not written down).

Probably some 140VAC.
And 6.3V for heaters, of course.

The PT is marked "PT-20", and the ouput transformer is marked "OPT-25"...what do the numbers stand for (watts?)?

No, just factory part numbers.

2. The resistor right after the diode recitifier is marked "5K6P1". The 1 is a subscript. So I assume 5K stands for the resistor value, but what does the "6P1" mean?

5k6 is a standard value, P1 *might* mean "Power: 1W"
Notice the output cathode resistor is labelles 130 *ohm* P6 which could mean "Power: 6W".
In both cases the power dissipation indicated is compatible with the position they are in; screen resistor and cathode resistor.

3. Someone else on this forum seemed to say that there is a voltage doubler circuit. I'm no expert, but I don't think so...who's right?

"Someone else on this forum"
Search "voltage doubler circuit" and compare them to what you have there.

4. Some of the resistors say "1/2" after the value...I assume that means it needs a 1/2 watt resistor, right? What do the other resistor watt values have to be?

Probably 1/4W .
Notice the 1/2W resistors are mainly standing high voltage, sometimes they are chosen so not for dissipation but for voltage rating.

5. The diodes are marked "5W-05C"...if needed, what would I replace them with?

Why would you?
But in any case, 1N4007 should do fine.

My main worry with this, and having been burnt countless times, is that when :

the owner says he doesn't know if it works or not.

it *always* means it does not work or at least has a deal killing problem, but since you bought it anyway , you can´t complain and must take the loss on your own.

I would run away.

[olddawg]

If you specifically want a "bedroom" amp that you can crank and don't care about Reverb and tremolo.... I would suggest you look for an Epiphone Valve Jr head (usually around $90 in prime operating condition) and run it through a 1x12" cabinet. At 5 watts it still might be a little loud without a speaker attenuator. But with a boost pedal (and possibly a compressor), it will scream.

[Justin Thomas]

Kustom made a nice little five watt amp a while back, had two channels and a master. For the hundred bucks my cousin payed it was pretty nice. Point being, check out contemporary offerings.

Justin

[rjb]

Point being, check out contemporary offerings.

Speaking of which, does anyone have any experience with these guys?
(I do know "Celestion" should probably be written in quotes, and they use SMT components- so might not be a joy to modify.)

5-Watt, 1x8 Guitar Combo Tube Amplifier with Celestion Speaker
https://www.monoprice.com/product?p_...oaAni9EALw_wcB

[olddawg]

They are all very similar. One 12ax7, one EL84, bridge rectifier. Chinese made. To me the limiting factor is the 8" speaker. I think VJs are better built with less hum (DC heaters), are easier to mod, and have 3 impedance taps. But honestly I have always just used the stock heads with the stock tubes. They are fine with a couple of pedals and will take your face off driven hard, lol.

[Mick Bailey]

Just taken a look out of interest and it is a voltage doubler circuit for the HT.

I hate to say this and will be burned alive, but at low volume I much prefer SS amps with a multi-FX pedal. I can go from Nile Rodgers to Dimmu Borgir in an instant. I find this kind of setup is far more fulfilling than a dry-as-cardboard tube amp turned down so low the background hum and hiss is louder than than what I'm playing. I had a little Zoom pedal recently that was so expressive through a Peavey practice amp I sat for hours and it improved my playing no end in exploring different styles and techniques. I even got feedback at 'dentist waiting room' levels. It's a far more satisfying way to get 'what's on the record' sounds.