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.
This circuit was found in an English magazine from 1981. We can still assemble it using BC548...
June 2017 - The new touch switches C & K KXT series can now be obtained from Mouser Electronics. These...
This oscillator, which can be used as a signal injector, was found in a Popular Electronics from the 90s....