Oram planned to use a simple op-amp feedback circuit and an external oscilloscope to become the waveform scanning oscillator. This design from an electronics magazine was to become the basis:
I reconstructed the circuit and used it with my analogue oscilloscope and found it to be quite slow and unresponsive. Often it would only scan the top half of the waveform. On interrogating the text a little further, the authors state that it is only good up to about 500 hz. The following image is the scope hood I constructed to test the circuit.
This post by nick's world of synthesizers illustrates the idea working really well using a vacuum tube based photomultiplier like the original Oramics Machine, instead of an LDR like the above circuit.