Bilateral current source 2 (CB20819E)

We found this circuit in an American publication from the 1980s. Equivalent modern operational amplifiers can be used.

Vox or Sound Switch (CB13609E)
I found this circuit in a 1978 publication. The circuit can be assembled with a BD136 transistor to...
TTL Digital Watch (CB19634E)
This basic TTL watch and minute clock circuit was found in European documentation from the 1970s....
555 Interval (CB20659E)
This simple windscreen wiper interval was found in old American documentation. The relay must have...