We found this code key or coded keyboard in a publication from the 90s. The circuit uses components that are still common today and is powered by a 12 V voltage according to the relay used.
This amplifier circuit with gain between 0 and 96 was found in the December 1983 issue of Radio...
This power step drains just 3.5 mA from the battery and can provide good playback on a 4-ohm...
This sophisticated circuit with a low, medium, and high treble filter is from 1990 documentation. The...