The 4720A VCO is a linear V/Hz Oscillator with ramp, triangle, sine, and square outputs. It is designed around a unijunction transistor and has minimal circuitry. This kit was $34.95 in the 1976 catalog.
This is information for the A version
4720A PAiA VCO Manual
4720A PAiA VCO Schematic
4720A PAiA VCO PCB Reference
This is information for the non-A version.
4720 (non-A) VCO Schematic
4720 (non-A) VCO PCB Reference
There are a few minor differences between the revisions that are indicated on this document
These are the bottom traces for the non-A revision.
I upgraded this 4720 to the A revision, upgraded the op-amp, and replaced the jacks. I also added bleed resistors on the output capacitors and upgraded the 748 op-amp to a LM301 (it requires the balance input). Although the power supplies are regulated, the current demand varies with the waveform so the series resistor adds some ripple back into the supplies. I chose to increase the filter capacitor from 100 uF to 220 uF on the VCO modules. The power cable terminates in a 4 pin MTA connector.
These are the four outputs from the VCO.
Here is an article from Polyphony February 1978 on modifications for a super VCO.
The customer wanted me to provide better trimmers for keeping the VCOs in tune. I replaced the Init_Trim trimmer with a 20 turn and brought the Zero trimmer to the front panel also with a 20 turn panel mount.