For those of you wondering how the bass tones are developed on your Farfisa compact (the black notes), they are simply the lowest octave notes sent through a filter. What I mean is, there is not another divider on the oscillator cards for those lowest octaves, those notes are just the same ones as the lowest octave but are routed through a filter before being sent to the outputs.The card with the filter is shown here:
The old high voltage capacitors shown in this picture, below, were completely dead in a unit I recently worked on, and this added a lot of hum to the outputs. These caps need to be high voltage because they filter the power to the tube pre-amp. Apparently the Farfisa used this style preamp because they wanted it to work with their pizo-electric reverb tank, which is discussed on this blog .
This style of tank was used for reasons discussed here.
Since the tank was completely destroyed in the unit I was working on, I did manage to get a more traditional spring reverb tank working in the farfisa, but it required that I add a preamp in the circuit to drive it, not on the recovery side but on the driver side.I also replaced the rectifier, shown here. It is a more modern one and I was ultimately able to attach it to the inside of the chassis for the preamp.