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 filter was found in an 80's English publication. However, it can be implemented with modern...
This circuit, which can be used as a shield, was found in old documentation. The circuit must be...
Found in Philips documentation from 1968 this circuit operates at frequencies up to 10 MHz with 76...