Door buzzer or alarm (CB20492E)

This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose NPN.

Commercial Receiver TS 600 (CB18378E)
This 6-transistor transistor radio was manufactured in Japan in the 1960s. It is a portable...
Signal Follower with Old Transistors (CB12922E)
This signal follower, from a publication from the 1970s, uses old germanium transistors such as...
Crystal variable oscillator (CB9506E)
Found in Radio Electronics from the 90s, this circuit can vary the frequency in small values...