This circuit is from an old Japanese publication of 1962. The circuit uses two batteries, one for the filaments of the tubes and the other one of high voltage for the plate circuits.
When the temperature rises above the value adjusted by P1 the relay triggers on. The rated voltage for the...
This oscillator for frequencies up to a few tens of kilohertz was found in a 1970s documentation. The...
This small transmitter, found in a 1982 publication, sends its signals to an FM receiver placed...