This circuit was found in a documentation of the 80s, having didactic purpose. For R1 values between 10k to 1M can be used. Transistors are general purpose types.
This circuit is intended to measure the power of a transmitter for the citizen's band (11 meters or...
This metronome can use either a high impedance phone or a crystal phone. You can use a small...
The circuit shown in the figure modulates a low power infrared LED with TTL signals. The circuit can...