You are absolutely correct - My Osc schematic bears little resemblance to the RCA - particularly with regard to the charactaristics of "L1". I simply knocked this simulation together as a quick first thought for evaluating the Armstrong oscillator.
As I see it, the "tickler" winding (L1:B) should have little impact - but I could be completely wrong about this.. my view is that, as long as it is capable of maintaining the required feedback to keep the oscillator oscillating, anything would work.
As I see it, the critical requirement is to get the value of L1:A and the tank capacitance C2 the same as the RCA if one wants the circuit to respond to antenna capacitance (via the antenna EQ circuit) the same way as an RCA.. It is the respective values of the tank resonator and the antenna resonator which should determine this - so I have kept these the same as the RCA..
This oscillator could be changed to work at EW frequencies by changing the values of L1:A (using pins 2-3 rather than pins 1-3 for L1:A) and C2, and replacing the antenna EQ values to those on the EW, for example.
It is only because Uncle Howie seems to think the oscillator design is critical (as in, Armstrong + the same LC arrangement) that I bothered to explore this - And the results are interesting.. This oscillator is simple and seems quite reliable ON SIMULATION.. But I really cannot see anything which particularly places it in any "special class" except perhaps the following:
What my circuit does not emulate is the somewhat strange configuration at the tank capacitors of the RCA - Referring to the above diagrams, it can be seen that my tank capacitors (C2) are taken to 0V, whereas the RCA tank capacitors (C1+C2) sit between the plate and the grid - I do not understand this (someone knowlegable on tubes could perhaps help me out and explain how this is working?).
The other factor I notice about the RCA circuit, which is different to most (if not all) transistor (certainly BJT) circuits I have seen, is that it looks like impedances will be a lot higher.. One has the antenna EQ connected to the tank resonator as expected, the "strange" tank capacitor configuration which, as I see it, has these capacitors connected not to a fixed ground but to an active driven signal which is contra-phase to the signal on the grid, and one has the oscillator connected to the high-z mixer grid..
Apart from the tank capacitors and "losses" to T8(3-4) the whole tank side looks like it could be much higher z than the tank circuits in most transistor designs.
Looking at C1+C2 and the connection to L1:B, (and not fully understanding whats going on) - I can see that the L1:B may be performing a function more than just providing required feedback - and that, in this case, the inductance / ratios etc WRT L1:A could be important.
My Osc schematic does nothing special - it produces a clean sine wave, thats all - IMO, it does not warrant further evaluation as it stands.. The Moog EW Osc is, IMO, a better choice..
The only area which may warrant further investigation is whether my different wiring of the tank capacitors changes anything substantially, and whether it is possible to "copy" the RCA configuration, and whether this has any advantages.
w0ttm.. Thanks for posting that simple RCA Osc schematic - it really helps discussion!