really?

Question

While repairing some old oscilloscope I studied its schematic a bit to learn how they managed to build it just with 3 tubes (though one of them was double-triode). Here horizontal sweep (scan?) generator is a rough sawtooth using single pentode.

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Here I "unwound" and redrawn it for clarity. I even recreated it (using different pentode - so resistances may not be finely tuned) and it works, with period roughly matching the order of R*C in the control grid part (on the left).

Brief schematic description says it is "designed using transitron scheme". Well, looking at wiki:

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I feel doubt as transitron should have screen grid (second) as the output, while control grid is not used actually.

Here in turn it looks more like tube with fixed screen and suppressor grids is fixed to some kind of bi-stable which is driven up and down by R-C chain feedback from anode to control grid (somewhat similar to NE555 or square generator using opamp / comparator).

Could anyone please direct me to some detailed description of this approach and perhaps comment whether it is good to call it transitron schematic. I'm unsure as wiki says the idea was implemented in several forms by several people so what actually is called transitron - either the whole oscillator with LC part as shown in wiki - or just the tube with screen grid pulled up and linked via capacitor to suppressor grid and, supposedly, demonstrating negative resistance similar in form to that of lambda-diode.

Thanks in advance!

RodionGork · Accepted Answer

As a follow-up, I found few more circuits of the same type browsing oldbooks and googling for "tube oscilloscope" and now I believe the authorof the original description was really confused for supposedly thisschematic is some variant of what is called "Phantastron". Still I hopeto learn a bit more about it and perhaps research a bit more,practically.

really?

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