In this video we'll follow the service, modification, and demo of a c.1970 Teisco Express 7, aka the Checkmate 18. Originally this amp had two 7189 power tubes, a 6CA4 rectifier, a 6AV6, and two 12ax7. A previous owner added a 5V transformer and an octal socket for using a 5Y3, 5U4, or GZ34 rectifier. When I got it, it had no tubes and the amp was out of the cabinet. I dropped in a 5Y3 and a pair of old Mullard El-84. It needed several caps anyway, so I just recapped the entire amp. The original caps were mostly Shin-Ei and Rubycon oil caps, so they really needed to all be replaced anyway. Also, the tone was somewhat shrill at first, which I surmised was largely due to the tone stack, so I modified the tone stack with a more Marshall-like bass control and midrange setting and changed some other values to pump up the overall gain. The original Teisco labeled AlNiCo speakers were not really helping, so I changed them to a set of 70s Fender labeled AlNiCo CTS speakers from a Super Reverb. The tremolo and reverb were not working when I got it, but it turned out to be a cap issue.
This amp now has a nice, well-rounded tone with good output and nice breakup when pushed. Excellent note definition, especially with single coil pickups.
Schematic: http://elektrotanya.com/PREVIEWS/63463243/23432455/oldies/egyeb/teisco_checkmate_18_audio_pa_reverb_sch.pdf_1.png