This circuit is from a 1975 RCA tube manual. It appears elsewhere on the site. R5 depends on the voltage of the amplifier with which it is used and can be changed.
This circuit is used to protect an amplifier from excessive power output that would cause problems for...
This circuit was found in a French magazine Toute LÉlectronique from 1978. Transistors are not...
This circuit was found in documentation from the 50's. The circuit uses transistors of the time...