We found this circuit in a Popular Electronics of the 90s. The circuit can be easily mounted today, as the components are common. The SCR can be the TIC106.
An oscillator whose frequency can be adjusted between 500 Hz and 5 kHz with the use of a...
This circuit protects the speakers in case the amplifiers have problems. With a continuous voltage...
This circuit is from the 80's and can be implemented with modern equivalent components. R1 is 2M5,...