Light test (CB8789E)

This light-sensing probe was found in a 90s Popular Electronics. The circuit detects light sources by triggering a buzzer.

Airflow detector (CB7427E)
Found in a Popular Electronics from the 1990s, this circuit uses components from National...
DC static switch (CB9257E)
This circuit was found in Motorola documentation from 1968. SCRs can be modern equivalents and the...
Noise canceler (CB8774E)
Suggested by the 90s ARRL Handbook edition, this circuit aims to reduce or cancel noise at the...