[Thursday] New aquisition

[Chris Prata]

I found a Marconi set with related accessories in the classifieds. It looks like an early 30's or late 20's tube receiver, medium wave but not sure. Working to ID it.

 But also, the set came with two other wooden box accessories. One looks like a nicely done possible homebrew tuner. It has a variable capacitor with a second "vernier" (fine tune) section, two air winded braided wire coils which rotate inside each other - those need work - and a 4-pin RCA diode tube with a 3v (dry cell capable) filament, unknown if good.

Presumably this unit works like a tuneable crystal set with the vacuum diode instead of a crystal.

What band does this cover?  I got to thinking, based on past experiments, and determined that it functions as an LC circuit, with the inductor and capacitor adjustable. Although an LC circuit would be tunable with either side adjustable, I dont know why there are so many 191x - 192x units that have one or more tuneable coils, perhaps for "pre-selection"?

To find out what frequencies this would cover, I plan to test the capacitance range of the plate capacitor and the inductance range of the adjustable wire coil section, and do the LC calculation for a bottom and top frequency this circuit will resonate at.  This is a little more complicated by the 10 position coil tap switch.

The 199 tube filament has a potentiometer (and a fuse) on it as well and the grid pin has a mica capacitor as well.

If I can test the tube, this unit may end up working.

I think the second aux 2-tube unit may even be an audio amplifier but not sure yet.


This may be a good experiment we can do at the museum someday as part of a radio education series.





-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://host194.hostmonster.com/pipermail/thursday_newsm.org/attachments/20190812/1e5ba26a/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20190811_211338.jpg
Type: image/jpeg
Size: 204544 bytes
Desc: 20190811_211338.jpg
URL: <http://host194.hostmonster.com/pipermail/thursday_newsm.org/attachments/20190812/1e5ba26a/attachment.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20190811_211346.jpg
Type: image/jpeg
Size: 252906 bytes
Desc: 20190811_211346.jpg
URL: <http://host194.hostmonster.com/pipermail/thursday_newsm.org/attachments/20190812/1e5ba26a/attachment-0001.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20190812_095902.jpg
Type: image/jpeg
Size: 221843 bytes
Desc: 20190812_095902.jpg
URL: <http://host194.hostmonster.com/pipermail/thursday_newsm.org/attachments/20190812/1e5ba26a/attachment-0002.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20190812_095940.jpg
Type: image/jpeg
Size: 335711 bytes
Desc: 20190812_095940.jpg
URL: <http://host194.hostmonster.com/pipermail/thursday_newsm.org/attachments/20190812/1e5ba26a/attachment-0003.jpg>