This small switched regulator was found in an 60’s Optical Electronics. The circuit uses an integrated from the time, which is difficult to obtain today.
This small transmitter was found in a 1988 publication, but it can be easily assembled today. The...
The frequency of each note depends on R2, which must be replaced by a keyboard. The circuit is...
This circuit is from a 1976 amateur radio manual. The transistor can be the BD136 and the...