[Milsurplus] Tuned circuit design question

[J Forster]

I've been asked about reverse engineering a WW II captured set. It's an HF regen
receiver with 4 bands. The front end has a main and FB coil. From a pic, the FB
coil appears to be wound on a bakelite tube that slips inside the main tuning
coil which is wound on a somewhat larger bakelite tube. The main coil is tuned
with a 140 pF capacitor in parallel with it, and the FB is adjusted with a 5 -
35 pF series cap. One end of both coils is grounded.

Now comes the tricky part. Both coils are tapped and there is a bandswitch which
grounds a part of each coil for the higher bands.

The question is, how do you calculate the inductances, when a part of the coil
is shorted out? Do you just assume the flux is totally excluded from the shorted
section and just compute the inductance of the unshorted part or what? Is there
some applicable correction factor?

I think, but don't know, that the coils are both single layer solenoids.

Thanks,
-John