This circuit is from a 1978 Texas Instruments optoelectronics manual. The trimpot adjusts the LED current. Other currents can be adjusted if they are within the capacity of the FET.
This transistorized circuit is powered by a voltage of 6 to 12 V providing high voltage for a neon...
This circuit is from an Electronics World of 1968. The transistors are of the time and the power...
This circuit is from a 1972 German magazine Funkshau. The circuit can use BC548 transistors...