This circuit was found in RCA documentation from the 1980s. The circuit uses LDRs of the time and the 50 uA instrument has zero in the center. R1 and R2 may have 2k2 and R3 10k typically.
Suggested by an American documentation for 1969 neon lamps, this circuit provides SCR control with...
This circuit was obtained in a 1976 amateur radio manual. The circuit can be made with a 2N2222...
This circuit was taken from the 1974 Ferranti transistor manual. It is intended to use a common...