Just so you can appreciate how hard it was to create electronic music in 1963, I tried to replicate the Radiophonics Workshop “Keying Unit”. It’s basically a way to trigger each individual oscillator.

The version here has five oscillators. Each column has the OSC, ADSR and filter in the top row. The middle row has knobs for filter cutoff and tuning of the oscillator.
Bottom row is a big button to trigger each oscillator.

The Tape recorder section is basically the same from the previous Radiophonics patch (I replaced the third tape machine with the looper instead).

Here’s some info about the keying unit taken from https://whitefiles.org/rws/r02.htm:
“Dave Young each created a device known as a Keying Unit . This consisted of a rack of oscillators and a small musical keyboard containing the special electronics, the latter containing keys removed from a cannibalised piano. One of these units contained nine Jason oscillators whilst the second, with an extended range provided by twelve Advance oscillators, was used by Delia in the creation of the Doctor Who theme tune.

When a note was pressed on the keyboard, a voltage was applied to a variable-mu pentode valve that fed the output of the appropriate oscillator to the final output. Since instantaneous switching would have been unacceptable, adjustable timing circuits for ‘attack’ and ‘decay’ were provided.

Unlike any other electronic instrument, this device allowed each note to be tuned to a unique pitch, allowing unconventional musical scales to be adopted. And, as a precursor to the future, the variable-mu pentode acted as a form of voltage-controlled amplifier (VCA).”