Found in a 1968 Mullard manual, this circuit can function as an infrared audio link. The transistors can be the BC548.
This Philips circuit of the 70's makes use of components of the time. The DZD40 is an uncommon...
This circuit suggested by Motorola can be used as LED high frequency modulator. One possible...
Suggested by General Electric in a 1965 documentation, this circuit can use the TIC106 as an SCR....