Intercom (CB21660E)

This good gain circuit was found in a Popular Electronics from April 1967. The transistors are germanium of the time.

Impedance Matcher (CB14462E)
This circuit matches a source of high or medium impedance audio signals with a low impedance...
Telephone extension alert (CB8627E)
Found in a 1993 Electronics Hobbyst Handbook, this circuit uses components that are still common...
555 Pulse Width Generator (CB25959E)
This pulse width-tuned circuit was found in the March 1996 issue of Electronics Now magazine. The...