Making our own stylophone

After I saw a design for a DIY stylophone in an electronics magazine, a friend and I made our own. As I recall the original design called for a unijunction transistor for the relaxation oscillator. The UJT oscillator was to get a very short discharge time so that the period would be proportional to the charge time, and therefore controlled by a resistor in an RC circuit. The contact pads which were the "keys" were taps into a resistor chain.

UJTs were expensive so I devised a replacement using a pair of BJTs (conventional transistors). The oscillator was followed by a binary divider to square up the waveform. We made several of these instruments and sold some to friends.

The kid in the first photo is probably my niece. My brother-in-law is at the edge of the picture. In the second photo you see a bit more of the top of the stylophone. The person was a schoolmate whose name is lost to me now.

I remember using my knowledge of the equal tempered scale with its twelfth root of 2 ratio between adjacent semitones to work out the resistor values needed in the chain.

This was probably the first model with a wooden box (cigar or chocolate box). Later versions used a long cigarette pack gift box. Getting hold of suitably sized boxes limited our production capacity.