This simple teaching circuit uses 5 transistors in a monophonic organ version whose notes are individually adjusted. The circuit is from a 1974 publication, but it can be implemented with BC548 transistors instead of the original ones. The 0.05uF capacitors can be modern types of 47nF and the supply can be made with voltages from 6 to 9 V For greater power, using a 8 ohm speaker, change TR5 to a BD135. The number of keys can range from 7 to 14 typically.
