Signal Tracer and Capacitor Tester (T1241E)

This mains powered two-in-one instrument was found in a Radio Craft from March 1948. The headphone must be high impedance.

Intercom with telephone (CB7829E)
Old phones with dials can be used in a simple home intercom system, as this circuit from Popular...
Transistor audio mixer (CB8759E)
Found in a 90s Popular Electronics, this mixer can be expanded to more channels. Transistors can be...
Grid dip meter (CB8215E)
This sophisticated circuit for several wave bands was found in a QST magazine for radio amateurs....