We found this sophisticated meter circuit in an article in Radio Electronics magazine from June 1959. The article taught how to assemble it. Transistors are common types at the time.
This basic configuration can be found in a lot of articles on this site. In this case, the relay...
This circuit is from American documentation from the 1980s. The transistors are general purpose...
The circuit is simple, as it uses only one transistor and a relay that can be MC2RC1 or MC2RC2,...