1-Ttube reflex receiver (T1555E)

This one-tube circuit is equivalent to the previous one. We find it in a 1924 book by Gernsback, Power is made by batteries.

Instrumentation amplifier (CB7029E)
Found in an Elektor from the 90s, this circuit is suitable for viewing audio signals on an...
Signal Injector (CB16330E)
This project was found in a 1982 publication, using only two transistors. Signal injectors are...
Process control interface (CB8995E)
Found in documentation from the 1980s, this circuit uses components from that time. The circuit is...