4093 Sine Square Converter (CB26335E)

Found in a Popular Electronics from the 90s, this circuit operates up to about 5 MHz input.

Dip Meter with Tunnel Diode (CB23881E)
This is the circuit for the HM-10ª, an instrument sold by Heathkit. The circuit is from a Radio...
Undervoltage Indicator (CB4988E)
This circuit indicates when the monitored voltage drops below the value determined by the divider...
CMOS Drive for Low Level Activation (CB13778E)
This circuit, from a 1975 Motorola manual, uses a power Darlington transistor of the time. We can...