This circuit was found in a Popular Electronics from the 90s. The transistors are general purpose, and the gain depends on the ratio between R2 and R1.
This circuit activates a relay that has a lamp as a load. The circuit is from a Radio Electronics from...
This circuit was found in an English publication from1979. The circuit can be assembled with a...
An oscillator whose frequency can be adjusted between 500 Hz and 5 kHz with the use of a...