I just started researching this as you recommended. Is it possible to make one small enough for the lamp project? When I think of a Variac I think of a large Toroidal coil transformer with a large knob on it.

There are some very small variacs. I have one that is only about 3 inches in diameter. Consult E-Bay.

They are usually called "magnifiers" for some reason. People still occasionally build them but it seems that they are needlessly complex and take up more space than standard 2-coil designs. I haven't seen any evidence that they out-perform standard 2-coil designs.

Thanks for that key piece of info lol.

Now that I have something to go off of I have found more information. I even found a thread you posted with an interesting paper about this, that nobody replied to sadly. The paper talks about people continually copying old ideas which really resonates with me no pun intended. I intend to do weird stuff with tesla coils, or maybe I'm not smart enough to know what's a bad idea. At least I'll probably try something nobody has seen before, maybe someone will be entertained by it. I will investigate this extra coil further and see if there's anything to it.

Tesla himself had some interesting theories but of course it's hard to separate the fantastical from the practical; however I am inclined to wonder about things he insists upon based on his track record of innovation, even though a lot of his ideas were proven to be bunk.

Thanks.

Hi Bob. Nice project you got there.

Here are some suggested baby steps, inspired by looking at the datasheet you sent.
Can you connect a regular 120-volt 60-Hz source to both the A and B inputs?
That should make the pointer go to 12:00, or to 6:00 when one pair is swapped.

If that's successful, the next step is to determine the A and B input currents.
If they are really more than an amp, you can measure them with a clip-on ammeter.
Otherwise use a multimeter on AC-amps mode, in series.   Or install a current-sensing resistor and measure its AC voltage drop.

With or without the current measurement, I bet you can make pointer go to a deterministic intermediate phase by putting a suitable capacitor in series with A or B input.  From observed angle with some different capacitors you can learn about the instrument's input resistance and inductance.

Active circuit design can wait till those exercises are successful.
As an alternative to active circuits, one might be able to move your 'scope pointer arbitrarily by properly connecting an AC synchro (selsyn) motor like the demonstration set on a shelf here.

[edit] this reminds me of unfinished project to generate 120 volts AC at slightly nonstandard frequencies, to demonstrate vibrating-reed frequency meters.

https://waveguide.blog/history-tesla-coil-geometries/

This article goes into some detail about it. Tesla seemed to think the third “freely resonating” coil could make “bigger sparks”

Googling this comes up with basically nothing. Was this idea lost? Impractical? A bad idea?

Tesla said it will “be recognized later as a material and beautiful advance in the art”

There are also a bunch of cone Tesla coils he built. Makes me wonder what other unexplored coil geometry might work. In another thread I mentioned I’m going to try different geometries because it’s fun to build secondaries but I need to figure out how to make some self tuning drivers that I can hook up to different coils for testing.

The older onetesla interrupter that I have goes to 150us. No you're not wrong, if you're hitting the OCD increasing the pulse width further won't do anything because the OCD is cutting the pulses short once the limit is reached.