This old 4-channel circuit was found in the December 1994 Electronics Now magazine. The circuit uses a 556 as a modulator. Note the code programming key.
This circuit was found in a 1980s documentation. Q1 and Q2 can be BC548 and SCR a TIC106. The...
This is the circuit of an automotive voltage regulator from the 1970s. The circuit is entirely...
The circuit shown in the figure consists of an amplifier for stereo sources with Maxim's MAX9723...