Thanks, Tom. My impression is that UF2 is tightly focused on Ventures discography, rather than on gear and playing, so it was probably the wrong place to raise the question. The members are otherwise very helful. I did ask the same question in three Shadows forums and got very precise answers, including some of the leads I mentioned here. I think that is because the members there tend to play and very engaged in capturing That Sound. I am quite hopeful that the same type of discussion can take place at this forum.
The Fender amp did come with a manual, but it was thick only because it said the same two-page instruction in several languages! On tone controls, all it said was that these knobs adjust the treble, mid, and bass. Not helpful at all!
I wrote Frank Glionna, who runs Music Gallery, a guitar store in Chicago, is very knowledegeable, and has been very helpful on technical points, such as the availability of flat-wounds in the 50s and so forth. I have no connection with his store, but he has supplied guitars to our musical company (The Madeleine Cookie Company) and, recently, a Victoria Victorilux amp. I ordered the "Walk Don't Run" Jazzamaster and '56 Stratocaster that I mentioned elsewhere in this forum through him.
This is what Frank wrote:
"The Fender Re-issue amps, 59 Twin, 65 Twin all have the same tone circuit. This was standard among all Fender amps during that time frame & other amps such as Marshall, Vox etc. This is still quite common with guitar amps. It wasn't until companies like Mesa Boogie & others that offered tone pots that started in the middle & would either boost or cut that frequency.
The Victoria is old school. Just like the Fender amps. The pot might be a little more sensitive on the Victoria making it easier to dial in the tone you like but it works the same way."
As suggested here, there is no substitute to experimenting with the dials, but it is good to know what the baseline is, as Walt says.
My best,
Andy