[Thursday] New aquisition

[Chris Prata]

Hi Dave that is the same unit and I realize that you may have just taught me something which I did not know - that the filament voltage can be varied to adjust the gain between the Grid and plate, if I'm understanding what you said correctly.

I would like to see a curve on that, as there must be a beginning and an end and a curve in between to how far you can go with that.

Chris




On August 12, 2019 11:27:15 AM David Crowell <ka1edp at yahoo.com> wrote:

I've never seen tuning knobs like those in the first photo. They are almost always black and sometimes brown (A-K), but not white. Also, the vernier knob is unusual. The coil switch is typical of 1920's sets. I have a couple of home brew sets with switch contacts like that. This set might have been home built from a kit of parts. A factory built set of that era would most likely have had a Bakelite front panel.

I'm guessing photo 2 is not the inside of the box shown in photo 1? The rheostat in the center would have been to adjust the filament voltage to adjust the gain. It is usually easy to trace the wiring in simple sets like these and draw up a schematic diagram.

DC







On Monday, August 12, 2019, 10:06:13 AM EDT, Chris Prata via Thursday <thursday at newsm.org> wrote:


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.





_______________________________________________
Thursday mailing list
Thursday at host194.hostmonster.com<mailto:Thursday at host194.hostmonster.com>
http://host194.hostmonster.com/mailman/listinfo/thursday_newsm.org

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://host194.hostmonster.com/pipermail/thursday_newsm.org/attachments/20190812/b7001898/attachment-0001.html>