Astable 555 (CB21101E)

This 50% duty cycle configuration was found in a Popular Electronics from the 1990s. The operating frequency is given by C1.

Audio Amplifier (CB20021E)
This step of two transistors has a high input impedance due to the use of FET. We can use BF245 for...
Digital Timer (CB17006E)
This digital timer provides timings from 1 minute to 10 hours with indication on a 3-digit...
Sample and Hold LM3900 (CB14218E)
The circuit shown is suggested by National Semiconductor's Linear Applications Handbook. The base...