This circuit is from a 1975 RCA tube manual. It appears elsewhere on the site. R5 depends on the voltage of the amplifier with which it is used and can be changed.
Placed in the vicinity of a telegraphic transmitter (CW), this circuit produces an audible signal on...
This circuit for light data transmission (visible or IR) has a maximum speed of 1 Mbps and can be...
This circuit aims to recover electrolytic capacitors by applying currents higher than normal for a...