Classic cars forum & vehicle restoration.

[pigtin]

We've discussed it at length and I think it's some sort of manual uniselector. It's 4" x 41/2" x 4" and the box is mahogany. On the base it has GPO D.15. D.
234. Possibly meant to be wall mounted.

Can anyone help?


_________________
Due to the onset of my mid eighties I'm no longer sprightly and rarely seen in my Austin special. I have written a book though. https://amzn.eu/d/7rwRRqL

[peter scott]

I think it's a resistance box. I can't quite see the terminals but I think the links at the top probably short out one or other of the resistance sets so that you can select any single value or any combination of two values. I guess the input and output will be the two outer terminals at the top.

I suspect it's meant to be free standing for bench use rather than wall mounted.

Peter
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https://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[pigtin]

That's a possibility, I'll try the AVO on it after dinner... the only things slightly misleading are the brass lugs (can't be seen in photo) obviously for mounting somewhere.

Don.
_________________
Due to the onset of my mid eighties I'm no longer sprightly and rarely seen in my Austin special. I have written a book though. https://amzn.eu/d/7rwRRqL

[peter scott]

Hi Don,

Actually, looking at it again I think I was wrong to suggest that the links at the top short out the selected ranges. I see there is the number 25 in the centre link and probably two other numbers adjacent to the outer links. All the numbers will be ohms and the pegs in the links just short out the values like the 25 and the other unreadable ones. I don't know how the selector knob resistances will connect relative to the links.

Peter
_________________
https://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[pigtin]

Can't find the AVO, must have it at work will take it there tomorrow.
I think you've sussed it out correctly. The two larger screws at the top, each side of the shorting bars are the terminals.
_________________
Due to the onset of my mid eighties I'm no longer sprightly and rarely seen in my Austin special. I have written a book though. https://amzn.eu/d/7rwRRqL

[dalbuie]

I work for BT and maintain the website for the BT Archive collection. I'll send the image to one of the 'oldies' in the group who may be able to help.

[stuchamp]

It reminds me of a model train transformer.

[pigtin]

Hi Stuchamp. I think the principle may be similar to the toy train setup.

Remembered where my AVO was (In the 10/4) and subjected the 'Thingy'
to a good resistive prodding around the terminals. Yes, it would appear to be a box of graduated resistors but with an open circuit from one terminal.

Question remains: what was it used for? I know little about telephone systems but would suppose it nescessary to check for the amount of voltage drop in the circuits used before the invention of Fibre Optics? Over to you chaps.

Don.
_________________
Due to the onset of my mid eighties I'm no longer sprightly and rarely seen in my Austin special. I have written a book though. https://amzn.eu/d/7rwRRqL

[peter scott]

Hi Don,

It was almost certainly used as part of a Wheatstone bridge. One use could be for measuring insulation resistances. The bridge can operate with various multiplication factors. It can also be used for measuring capacitance or inductance. I'm just quoting from "Telephony" volume 1 by Herbert & Procter.

There are pictures of resistance boxes but not exactly the same as your one.
I can scan the text if you would like more info.

Peter
_________________
https://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[pigtin]

Hi Peter,

Can remember using a Wheatstone Bridge while training and actually recall a similar box... but that was 50 years ago and the old memory starts to dim. Seems you have provided the answers. I remember other measurement tools, meters etc' all made to the same standard. Cabinet makers reigned supreme in those days and it was unthinkable to put electrical instruments in a cheap box.

Don.
_________________
Due to the onset of my mid eighties I'm no longer sprightly and rarely seen in my Austin special. I have written a book though. https://amzn.eu/d/7rwRRqL

[dalbuie]

One of the CE (Connected Earth) partners has identified it as an early variable resistance box. Used for testing where you needed to create a specific resistance or where you were balancing a bridge circuit - once the circuit was balanced you read off the value of the resistance.

Porthcurno Telegraph Museum have a number of artefacts similar to this and I'm still waiting on a reply from them.

We've had a look through a series of product and equipment records in the archive and found a reference to "Bridge, Wheatstone non-reactive, ration arms". It shows mark number 234 and the year of 1915 and this could relate to the reference you quoted D.15(being the year) D.234(the model). There is also an associated specification drawing number (TG2038) which we also have in the archive in case this number is on the item anywhere.

Cheers
D

[pigtin]

That's absolutely brilliant Dalbuie, more info than I had ever expected to get... this forum really is the fount of all knowledge.

Many thanks. Don.
_________________
Due to the onset of my mid eighties I'm no longer sprightly and rarely seen in my Austin special. I have written a book though. https://amzn.eu/d/7rwRRqL