This narrowband data receiver is from the Philips Databook of 1990. The circuit is powered by 5 V and N1 has 3.21 turns, N2 1 turns with Q = 16.
This is the basic operational amplifier configuration for gain 10. R2 can be changed to other...
Instead of LED bulbs, LEDs with a series 470 ohm 1k resistor can be used in this 80's circuit....
This circuit is from a1970 documentation. R1 may have 10k and P1 47k. The transistors can be BC558...