An interesting old Coil

[pwdrive]

Alan, there's a Formo (presumably) coil in the Formo Screened Grid Three design, some construction notes and a picture of the coil which bears some similarity to the coil you have, details can be found in the link below, starting at magazine page number 463 (Wireless World) it might take a while to download the PDF.

http://www.americanradiohistory.com/Arch...929-05.pdf

Lawrence.

[Skywave]

L.W. tuning: with a 500 pF variable condenser, (almost the guaranteed value for his vintage), to tune to 150 kc/s requires an inductance of 2250 uH. With that value of inductance to tune to 250 kc/s requires a tuning capacitance of 180 pF.
The 2250 uH is greatly in excess of the total inductance available on that coil; the min. value of the variable condenser is far too high to suggest a straight-forward L.W. tuning arrangement, even allowing for added inductance due to mutual coupling.

Al.

[pwdrive]

Referring to the article I posted, the coil(s) looks similar to Alan's, they might be the same or maybe not, the coil as shown in Fig. 2 seems to me to have more sectional windings than the ones shown in the actual receiver, whicheverways both coil assemblies in the schematic are tuned with a 500 pf job.

I wonder what the band plan was back in the 20's ?

Lawrence.

[AlanBeckett]

Thanks Lawrence. That certainly looks similar. Now all I need is the Aerial version. Perhaps I could make one, that is the one I have without the Reaction Winding.

Yes, it was remiss of me not to measure the actual working Inductances.

So, measuring from 'Grid' to 'Earth' gives 1.53mH for both Coils and 160 MicroHenries for the MW Winding, ie with the LW Winding shorted out.
I also dug out a Baseboard Tuning Capacitor which measures 530pF fully meshed.

   

Assuming that the actual Range of the Capacitor is 30pF - 530pF I make that:-

LW - 743kHz to 177kHz or 404m to 1690m.

MW - 2297kHz to 547kHz or 130m to 548m

Of course that ignores Strays which will change things a bit, more so on MW I would think.

I'll have to look out a suitable piece of Ply, join them together and see where they tune. With an OA91 and a pair of 'phones I might even hear something.

Alan

[pwdrive]

"Daventry calling"

EDIT: Will it be an RF amp + regen det job or just a regen detector, or a germanium diode job ?

Lawrence.

[AlanBeckett]

Slow down a bit Lawrence, the Temperature down the Garage isn't compatible with life.
I'm pondering.

Alan

[Alan Douglas]

A pox on librarians who discarded ad pages. I can't open this volume far enough to scan, but I can take a photo:
   

[AlanBeckett]

That looks like it Alan. I wonder if SG1 and SG2 are the Aerial and Detector versions.
What's the Date of the Magazine and what does it say vertically against the Coil?

Alan

[Alan Douglas]

May 1, 1929 (same issue as the construction article), and high wave, reaction, low wave.

[Skywave]

Quick snippet: a response to Lawrence's post above.

A bit of research indicates that during the pioneering 1920's, there weren't any 'L.W.' and M.W.' bands as we know them today: it was a bit of a free-for-all: less than 100 kc/s to about 1Mc/s (those freqs. are approx.) and continuous throughout. There was a popular broadcasting freq. band (albeit small) centred on 448 kc/s, apparently. The L.W. (Europe) and M.W. freq. bands - as we now know them today - originated in the 1930's.

Al.