From Newsgroup: sci.electronics.basics
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.
https://imgur.com/a/r4uPTWR
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:
https://en.wikipedia.org/wiki/Dynatron_oscillator#Transitron_oscillator
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!
--
to email me substitute github with gmail please
--- Synchronet 3.21d-Linux NewsLink 1.2