Found in a 1970 EEE, this circuit can be applied to TTL ports. The supply is 5 V and the frequency, which depends on the crystal, can be between 1 and 3 MHz.
This decoder filter was found in a 1975 documentation. The integrated circuits can be 741. The...
This circuit is from an Electronics World of 1968. The transistors are of the time and the power...
This circuit uses a not easy to find IC these days. The circuit sources 15 W to a 4 ohm load and...