An interesting old Coil

[AlanBeckett]

Ah, so, late '20s then.

Alan

[pwdrive]

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

Like you said, stray C, self capacitance etc, there's also antenna loading as mentioned in the link below.

Here's the coverage specs for all that assuming a PMG Standard Antenna and a antenna coupling capacitor is used.

http://www.americanradiohistory.com/hd2/...22formo%22

Lawrence.

[AlanBeckett]

That's the Beast young Lawrence, splendid!
12/6d with Base my life. I bet that was a surprise in 1929

Alan

[pwdrive]

I did a specific search on that W.W. archives site for Formo, lots of returns but mainly for their variable capacitors (picture wise)

Apart from wot's already been posted in this thread, that last link is the only other one that shows the coil you have so far as I can find out.

Lawrence.

[pwdrive]

That's the Beast young Lawrence, splendid!
12/6d with Base my life. I bet that was a surprise in 1929

Alan

My first wage when I started in trade in '64 was £2/10s a week, that was a surprise too.

Lawrence.

[Yorkie]

That's the Beast young Lawrence, splendid!
12/6d with Base my life. I bet that was a surprise in 1929

Alan

Good bit of sleuthing by Alan Douglas and Lawrence to have ferreted out the info! Radio was certainly a rich man's game back in the 20s & 30s. 10 shillings in 1929 equates to £28.00 today, and 2 shillings for the base adds another £5.30. It's evident when looking at vintage components that they were made 'up to a standard' - not 'down to a price'. Interesting that the advert in WW infers that the coil and base were cheap, as they may well have been by the standards of the day in comparison to similar items.

http://safalra.com/other/historical-uk-i...onversion/

[AlanBeckett]

Indeed. Even for a DIY Wireless it wouldn't be cheap.
Coil, Base, Valve, Base, Components, Hardware, Phones, HT Battery, GB Battery and Accumulator would set you back quite a bit I would think.

Alan

[Alan Douglas]

Formo advertised their "Screened Grid 3" in January 2 and 16, 1929, Wireless World, and then the components ad appeared every other week, the same ad I photographed. I haven't looked in other wireless magazines. My 1928 WW volumes are bound without ads.

[AlanBeckett]

And then there were two :-)
Not really, as this one is different. The attraction was that it uses the same Base, but didn't have one with it, which is what probably made it unattractive.

           

There's no point repeating waht everybody can see except to say that I interpreted 'SPLIT SEC' as Split Secondary and '1000 - 2000' as the coverage, presumably in Metres.
And it does fit the FORMO Base.

   

So, what's it like Electrically? Actually like this:-

   

That was a bit of a surprise. It's easy to see that there's a smaller Coil between two larger ones, which I assumed were the 'Split Secondary'. What I hadn't expected was that they are two separate Windings.
The two figures for Inductance at the bottom of the Diagram are the two 'Secondaries' series connected either Aiding' or the other way.

So, what's it for?
The individual 'Big' Coils seem too low and connected together too high for what I assumed was the coverage.

Any ideas?

Alan

[pwdrive]

Main tuning (LW) + Tunable notch filter (LW) ?

Lawrence