What the heck is this thing??
Two of the leads measure 100 ohms and the other two measure 9.5k

I have another that measures 97 ohms and 3.7k

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I'd be guessing here. It looks like either a voltage regulator or some sort of nixie valve.

Hi Brad,

Some more info.

The 'bead' at the center has 2 wires coming out the top and 2 wires coming out the bottom and a further 2 wires that seem to be each end of a winding around the outside of the bead.

One top and bottom wire connect to one of the posts, the other top and bottom wires connect to the opposite post.

The 'winding' ends connect to the other two posts.
The 4 posts are 90 deg. apart from each other, forming a square.

The 'winding' measures 100 ohms and the 9.5k is across the other two posts.

Looks like a Daddy Long Legs trapped in a glass envelope!

Cheers,
Bob

This may be a daft idea but could this be some sort of delay-relay? The 9.5K bit forming a slow warmup time heater. The 100 Ohms doesn't fit the theory unless this bit is faulty I.E. not open or closed. Sorry if I'm wrong.
John

My first thought because of the suspended mass was an accelerometer. However because it appears to have a heater, being the lower resistance coil, Brad's idea of some sort of regulation device seems more likely.

The red marking suggests Mullard. Suppose nothing is legible.

Hi crew, thanks for the ideas so far. There can be no such thing as a daft idea when trying to work out what this thing does!

Most certainly the 100 ohms is a winding around the outside of the bead.
Under good light and loupe the turns are clear to see - about 10 - 15 turns of what looks like nichrome.

There is evidence of slight discolouration of the bead in both of them, which supports the theory put forward that the 100 ohms is a heater.

There is a clear marking on one of them - B53.
The B is fairly evident on the other, but is followed by what looks like 14.

They measure very differently across the high ohms connections [9.5k verus 3.7k]
So assuming they're not faulty, one would expect them to be marked differently.

All other markings have way too much missing to interpret.
Will try to get a tighter shot on the bead and post it up.

Cheers,
Bob

Here's a medicore close-up of the bead. Will try to get a better res. in daylight lighting.

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Hi Rob D.

I know it may sound obvious but if the device was used in a feedback loop, could it be used in an oscillator, or to control the bias current in a critical stage of some type of amplifier (a transmitter circuit perhaps) ?
I've seen light globes used in oscillators as a form of DC feedback to keep the distortion as low as possible.

It might be helpful to know the resistance between the "heater" coil and the other leads. High would suggest a ceramic bead; low...???

BobShep, yes, I'm also leaning towards some kind of temp stabilised device.

STC830, I can confirm that it is open circuit between the winding leads and other leads.
Also tried reversing the polarity of the meter with no change to any of the readings.

I might try a small amount of current through the heater and see if the resistance of the other connections varies.

Ok, more info to report.
Just 25ma through the 100 ohms winding causes the resistance between the other two leads to plummet to around 12 ohms.
Removal of the 25ma sees the resistance steadily rise back to where it started at around 3.5k.

So, it's at least a very sensitive temp controlled resistance.

I know it's very late in the piece but could the beastie be one of these?

http://www.trademe.co.nz/electronics-photography/other-electronics/electronic-components/sensors/auction-547822415.htm.

Ahhh well, there's our answer.

For those who are unaware, NTC = negative temperature co-efficient, ie: when the temperature rises the resistance falls.

This could be used to switch on cooling fans for example.

If you look in Ballast tubes & Barretters you may find it.

Where in the circuit is it? It is likely being used as a voltage regulator. I have actually handled one of them.

I think there may be one in the Radio Clubs collection, or in a set that a collector had for me to overhaul?

Marc