[morzh]

One more attempt to understand the L11 coil.

I measured it very accurately, made the drawing and used 3 different formulas. All three approximate square cross-section coil, which this one is not, the length of the winding is double the thickness or the average radius.

However even if the error is 100%, I would know the order of the value.

All three calculators give me Henries: from 2.5H to 4.8H, the third being in between, 3.7H.

So, it is not a filter after all; I think, as McLellan tried to explain in his R-7 Superette, which is very similar, the stage being used as the driver is the 2nd detector (which we know) and it simply lacks the oomph driving a smaller primary inductance interstage transformer, creating lots of distortion, so he used a larger transformer with the core rich in iron. R-7 also uses a choke like this one, but it is 80 Ohms and not 3000 Ohms.
So my impression is, they are trying to use that choke as an additional ballast, sacrificing load driving to get less distortions.


Anyhow, the coil is what it is, it is 3000 ohms of AWG39 (overall d=0.1mm) which makes it around 1100 meters length, and with the average R=9.75mm and N= 17,000 turns with air core this is what it is. A few Henries. At low frequencies it will be a simple divider between the choke and the primary, and since the impedance is low, and the primary reactance is across the load, it will lose a goodly part of voltage on this choke.
At high frequencies this choke will be in series with the leakage and the load. Not sure what the load looks like at, say, 5kHz, but if it is a few kOhms, maybe 10K, and then the choke will be about 15-25kOhm.

However, at high frequencies the effective reactance will be way less due to quite a bit interwinding capacitance - many layers, quite wide.

It is hard to predict without real measurements, which would be interesting to do.