This configuration similar to many of this site was found in 1965 General Electric documentation. Modern equivalent transistors can be used. LEDs can be used.
This circuit was found in a 1977 Signetics manual. The 556 consists of a 555 double and the...
One of the first transistor amplifiers with transformerless output but using a 45-ohm speaker. This...
With this simple converter found in a 1997 documentation, it is possible to tune VHF stations to a...