I got out the banged up Simpson (Series 6) 260 that I bought well used and decided to check the AC meter on the panel. It wasn't as bad as I thought - just sticky and slow - but reading accurately.

I put the random motion switch on High and centered the gain control on the noise generator. Then I put the Simpson across the panel meter. Watching it and striking a chord, I then lowered the gain control on the Whind side until the noisy note quietened. This ended up being around 2 VAC. (9 VAC is standard, but there's a service bulletin saying to set it to 6.)

The Tremolo is still working so I think I'll be leaving it like this until I work on the generator. At least it gets rid of the warbling tone (on the F# below middle C on Diapason).