Vintage Synth Repair

I'm restoring an old (late 50s early 60s?) Univox and I've noticed something odd about the wiring of the capacitors in the thyratron circuit.

From what I can gather from the schematic, it's using a thyratron as a simple AR envelope generator. The timing capacitors are switched in from a rotary switch on the front panel marked Circuit 1 2 3 4. Each 'circuit' has a different value capacitor switched in: 1, 2, and 4 are: open, .47uF, and 16uF. Circuit 3 though puzzles me, as it has 2 electrolytics wired in series - fair enough if they modded it to lower the capacitance, but they have their positive terminals connected together - inverse series. It looks like the original wiring - no sign of recent bodges - the caps are old Hunts cans - half of a 16uF dual can wired in series with a single 8uF axial. They have DC across them - the same as the other caps on 2 and 4.

To add to the confusion, both measure as 18uF on my meter, summing to 9uF in series. These haven't been powered up in years, maybe decades, so maybe there's some strange effect here caused by the drying, or have they somehow reformed themselves to the same value by being connected back to back?

I'm proposing to just replaced them with a single 4.7uF and see how it sounds.

Any suggestions as to what's going on?

Thanks
Susie

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