it has 2 speakers which both play different sound at the same time, which makes an interesting sound and it is tunable using the trimmer potentiometers so you could in theory make an accurate scale, the notes are also layed out like on a piano.
Another feature is a potentiometer that controls pitch bend and a rotary switcjh to change the capacitors on the organ, changing the sound.
Step 2: What you'll need
2x 555 timer chips
10k + 100k potentiometers
20 2k trimmer potentiometers
10n, 100n, 47n and 2 10uf capacitors
large perfboard (or you could make a printed circuit board)
assorted wire and battery clip
glue, cable tie and cork
probably desoldering pump/wick
screwdriver for the trimmers
Step 3: The piano circuit
The 100n capacitor is replaced by the rotary switch, with three capacitors connected. the wire from 6/2 goes to one of the middle termnals and other capacitors you want to use are connected to the other terminals of the switch and to ground. I used 100n, 47n and 10n capacitors but you could use more different values.