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Topic: Archaeological Electronics (Read 2090 times) previous topic - next topic

3dprinter

May 08, 2011, 05:39 pm Last Edit: May 09, 2011, 08:00 pm by Msquare Reason: 1
Attached picture. Found it in a junk pile for trash. OK, so before this picture was taken, I sanded it down a bit polished it and so on. And took the insides out. (Sorry about the strong shadow on the left sides) Question: What is it? The sign says
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European
Weston Electrical Instrumentation Co.
Newark NJ.  Berlin
NO. 8843
On the top there is written - very faint, so might read wrong - 300 and 1n on the spots next to each terminal.

My DVM reports opencircuit. The mystery item seems like a number of plates, seperated by mica, where each plate has a wire wound tightly, evenly (a mm or so) apart. It seems they are connected in series by the terminal at each end of each plate

My conclusion is that it is a 1nF capacitor for 300V, but it might be a calibrated resistor or ... ?

AWOL

#1
May 09, 2011, 01:55 pm Last Edit: May 09, 2011, 02:38 pm by AWOL Reason: 1
Does it say "Western" or "Weston"?

Weston were (are) instrument makers, IIRC.

Edit:
http://www.westonmeter.org.uk/thecompany.htm
(I completely forgot about the Weston exposure meter)

The presence of mica suggests (to me) high temperatures.
I would have said some form of rheostat - is there a slider of any sort?

3dprinter

#2
May 09, 2011, 08:00 pm Last Edit: May 09, 2011, 08:03 pm by Msquare Reason: 1
Weston - I'll correct the original post

No - it is very static. The Ohm meter show >10Mohm. Of course there might be a broken wire, and I've tried to probe accross two edges. Still nothing. Occasioanly the DVM showed a few hundred Ohms, but not in a consistent repeatable manner - I may be looking at flakey shorts due to my manhandling it.

Mica is also an excellent high voltage insulator. The cage is steel(?) on 5 sides (the bottom is just a frame holding the cage, but the top lid is wooden. So the cage is for ventillation, not a Faraday cage.

1nF makes no sense. If it was a calibrated (reference) resistor surely the value would be written somewhere.

Thanks for the link. On the other hand I am going to use the box for its decorative exterior and put something silly in the inside - no, not the "leave me alone", but some thing else equally "useless".

Grumpy_Mike

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The presence of mica suggests (to me) high temperatures.

But not from a capacitor. Mica capacitors have a temperature coefficient the opposite of normal capacitors and they are used along with others to make a capacitor with no temperature variations.

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My conclusion is that it is a 1nF capacitor for 300V,

The problem with that is the people didn't use the units of nF in those days its use is relatively new, it would have been called a 1000pF capacitor.


The label is just the manufacturer not what it is.

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it might be a calibrated resistor

But you said:-
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My DVM reports opencircuit.


However 300 ohm is an important resistance, that is the natural resistance between ground and the ionosphere and so a standard design of transmitters in the old days had a 300 ohm feed impedance. So it might be a dummy load for a transmitter. Which brings us back to the high temperature.


3dprinter

#4
May 09, 2011, 08:39 pm Last Edit: May 09, 2011, 08:41 pm by Msquare Reason: 1
Well  your response has made me probe a little more, and I now get a repeatable reading along one "plate" - 1K Ohm. There are 19 or 20 plates and the resistance adds up when I measure accross several. Shame, I liked the 300Ohm theory.

Each plate has the wire and is covered in some black material - laquer or pitch or whatever. I do not think it is intended to run at anything except room temperature. Length 12 cm, height 4 cm. The assembly is about 6cm thick.

I took another picture - better camera - of the innards.

AWOL

Caps don't tend to get that hot, so I can't see the point of the case's ventilation holes - I'm still with Mike.

Caps also tend to use plates, even if they're wound in a spiral, not wire

JChristensen

#6
May 09, 2011, 09:28 pm Last Edit: May 09, 2011, 09:30 pm by Jack Christensen Reason: 1
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The problem with that is the people didn't use the units of nF in those days its use is relatively new, it would have been called a 1000pF capacitor.


"pF" only came into common use here in the US maybe 30-40 years ago. Before that, they used "micro-micro-Farad" instead (e.g. 100 ??F).

Anyhoo, some sort of dummy load, RF or otherwise, would be my guess. I wonder if 8843 is a model number or a serial number. No other identifying marks, dates, etc.? Nice job spiffing it up! Hope you figure it out, I'm curious about it!

The sides are pierced metal, correct? Would not hold liquid? The innards almost look like they could be battery plates, but if that were the case, I'd expect things would have been pretty corroded.

Grumpy_Mike

Check the spiral windings, if it were a dummy load you would find half of them go clockwise and the other half anti clockwise so that any inductance is cancelled out.

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