Found in an English publication from the 1980s, this circuit can be built with equivalent transistors such as the BC549. The signal must be applied to an external amplifier.
A little more complex than the previous one, and can now be called a shield, this circuit can be...
Although not using transformers, this amplifier may have difficulty mounting if the original...
This zero-crossing switch circuit triggers an SCR when the input voltage goes through zero. The...