The frequency of each note depends on R2, which must be replaced by a keyboard. The circuit is from Radio Electronics from April 1980. The power supply is 9 V for the amplifier used.
This SCR relaxation oscillator was found in an 80's Electronic Design. It flashes a small...
We found this shield circuit in a 1991 technical documentation. The phototransistor can be...
This circuit for old photo enlargers was found in a 1970s RCA manual. The components are from the...