This circuit is from a 1969 Electronics World. The transistors may be modern general-purpose equivalents. The circuit is for frequency ranges between 250 Hz and 250 kHz.
This circuit was found in an old Popular Electronics. With it we can check the operation of a...
This circuit triggers a relay when the set temperature is reached. The circuit is from an old...
Suggested by General Electric in a 1965 publication this circuit uses a light bulb. Can be changed...