Teisco Checkmate 45 schematic

Gudmund

Member
2010-02-27 7:13 pm
Please help....a 1960- 1962 Teisco Chekcmate CM45 need repair after having burned a pot for the negative bias ,some caps and the oscillator coil...I have the CM 50 schematic but its not the same amplifier. CM 50 uses a 12AX7 to drive the Piezo reverb-tank.......but the CM45 has the real deal reverb-tank and uses a ECL82 to drive the low impedance 22K reverb...at least I think?


Several cobber-lines has been scratched away on the driver borard, and the amplifier is really a mess inside..more than one wire renewed but in wrong places...thats clear...


Please help with the Teisco CM 45 schematic:confused:


Rgds Gudmund
 

Attachments

  • IMG_20191202_195106[1].jpg
    IMG_20191202_195106[1].jpg
    911.6 KB · Views: 98

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
> not the same amplifier

How different can it be? Look at other Teiscos and Elks for one with a transformer reverb. Compare amp to schematic and note all certain and ??? differences. Use basic troubleshooting and "usual" tube voltages to guess what works OK and what looks wrong.

The CM50 plan attached has a MAJOR error. The negative bias for the output tubes has a dot at the B+ line; this is wrong. Bias comes from the negative supply for the tuning oscillator. If this tuner is bad, get a Casio tuner which is more accurate.
 

Attachments

  • teisco_checkmate_50_pa_reverb_sch.pdf_1.png
    teisco_checkmate_50_pa_reverb_sch.pdf_1.png
    447.9 KB · Views: 93

Gudmund

Member
2010-02-27 7:13 pm
> not the same amplifier

How different can it be? Look at other Teiscos and Elks for one with a transformer reverb. Compare amp to schematic and note all certain and ??? differences. Use basic troubleshooting and "usual" tube voltages to guess what works OK and what looks wrong.

The CM50 plan attached has a MAJOR error. The negative bias for the output tubes has a dot at the B+ line; this is wrong. Bias comes from the negative supply for the tuning oscillator. If this tuner is bad, get a Casio tuner which is more accurate.


Hi PRR


My friend, I am writing this for my friend who tries to repair the CM45......


... thanks for the schematic of the CM50, which we already have. We have noticed the error in the drawing. But you see, we are not educated tech's and have only worked with hifi tubeamps. In hifi tubeamps you don't use a oscillator and a reverb-tank between the amplification stages.

In this CM45 there is a mess inside after some components has burned the oscillation coil, the pot for the negative bias and some of the wires.

Two younger tech's has tried to repair the CM45 without any luck, and it looks like some of the wires has been replaced wrong?

So far my friend have managed to get the ouputstage working and the amplifier plays beautiful tones, with signal input after the reverb-tank. But from the negative supply he think a wire connection is missing to the driverboard. The negative bias works fine for biasing the output tubes 7591, but somewhere on the driverboard a wire from the negative supply is missing....he think's


A original schematic would be very helpful


Rgds Gudmund