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 circuit is from an English magazine of 1977. The circuit is still current, just using a TIP41...
With a touch of the push button the lamp is switched on. A new touch and the lamp go out, in this...
The transistor for this flashlight brightness control may be the BD135. The circuit is from 1978...