Posted this on Reddit, thought I would put it here too cause why not.
https://www.reddit.com/r/AskElectronics/comments/1pzrlwb/vacuum_tube_oscilloscope_project_what_does_this/
Anyone have good knowledge on vacuum tube scopes? There is a 2 meg pot on the plate of the 884 that I don't really understand.

This is a very crude X-sweep sawtooth oscillator made of 884 thyratron tube and adjustable RC network. R is 300K + 2M potentiometer, C is selected with a rotary switch.

So, 2M resistor adjusts X-sweep rate within selected timing capacitor range.

The circuit is generally nothing more than a classic NE-2 neon lamp flasher, except the fact that 884 allows ignition voltage threshold control by a grid voltage (go google a 884 datashhet) and thus having X-sweep to sync.

2M resistor simply adjusts capacitor charging current (from 450V bus) for sawtooth.

BTW there is a small error in your circuit. You are missing a comma for 884 cathode bias voltage value. It is 6.5V, not 65V as on your schematics, though 20K / 650 Ohms values for bias voltage divider are correct.

@RRK
Thanks so much, I think there is a decimal point between the 6 and 5 but the quality is so horribly low that it isn't very visible.

Good luck building this. The circuit is of course not overly complicated, and may be some fun. IMO, the major obstacle is to find some suitable transformer with necessary output voltages. I'd try to use some modern off-the-shelf DC/DC HV converter modules, though impulse noise requires some care, as it can spoil the circuit!

Thanks! I actually already found a working used transformer on Ebay that was almost exactly what I needed. Except one of the windings that needed to be 5V was 6.3, but it was just for a rectifier so it was easy to replace the type 80 that it asked for in the schematic with a 6AU4 I had.

The transformer also has another winding of probably over 1kV, and I fried my cheap meter trying to measure it  . It isn't used here since the 902 CRT operates at a maximum of only 600V. This transformer was almost certainly used in a scope in the past.

You should consider this a lucky find, I was restoring a Soviet tube scope, somewhat local clone of Tek 310, out of nostalgic reasons. Brought most of the circuitry to working order by replacing all of the paper capacitors and some other minor parts around, CLAing the switches, but was stuck with half-dead power transformer having deteriorating paper insulation. Original transformer has circa 12 windings (!) about four heater windings, ~three anode ones and two high voltage.  So far the oscilloscope works on "the external life support" feeding substitute voltages from some extra transformers outside but that is far from complete restoration.

From what I have heard from my limited experience in the VT community, a dead transformer on a rare device is practically a death sentence in terms of a restoration. I wish they made standard transformers with incremental plate winding voltages to make them just a little more interchangeable.

I was ecstatic when I found that transformer on Ebay, if I didn't find it I would definitely not be doing this project.

The schematic also calls for a 30H filter choke, which was prohibitively unobtainable. I am hoping that with a ~50uF cap instead of an 8uF cap I will be able to get away with a 2.5H choke that I have. It theoretically shouldn't hurt the rectifier since it is after a resistor, first filter, and choke, but we will cross that bridge if we get there. We shall see.

In the Soviet time, there was a great series of local TA/TAN/TPP universal transformers intended for anode, anode/heater combo and low voltage semiconductor devices, respectively. Even D series of standard inductors. Naturally, hundreds of types. A feature was multiple secondaries sometimes with taps, allowing to combine them to get pretty whatever voltages you need. Still, many NOS or removed transformers from these series circulate. Some even made today, but as most were made in Nikolaev, Ukraine, the supply is mostly cut-off.

I believe this was pretty unique in the world, almost everyone who did electronics in Soviet or early Russia (and around) was familiar with these universal pre-made transformer series and had many, including me. I picked a 4x 6.3V heater transformer for my scope restoration, for example.

As for modern inductor substitute, yo can use a high-voltage MOSFET as a source follower trick. Until input ripple is not extreme, you can use a passing MOSFET with a gate grounded via some capacitor and some resistors/zeners around. MOSFET will drop some voltage, slightly larger than ripple peak-to-peak, and provide a clean voltage at source. Okay, this can be done with a tube too, but in a bit more complicated way

Sometimes you can also use high voltage zener to regulate/stabilize a voltage, as I recently did with a string of 50V/1W zeners. Really high voltage zeners in the 300-400V range do exist too, but usually are quite noisy/bad-behaving in practice.