We found this circuit in Mullard's 1960s transistor manual. No information about transformers is given. Transistors are germanium types of the time.
These basic filters, the second one being operational, were published in the November 1973 issue of...
Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime...
This servo circuit was found in 1969 Motorola documentation. Integrated circuits and transistors are...