Resistor switch box curiosity question

[Witty]

I bought this resistor box recently on Ebay. It seems to have 3 switch buttons to switch between resistance values, plus an external probe insertion connector.  My goal is always to restore items to original working condition if possible and this appears to be completely intact. I would love to verify it's purpose. It's a very curiosity question. I have attached a photo of the schematic, plus photos of the resistors and the pushbutton controls.
My biggest question; what probe connector would have been inserted into the jack and for what reason.
Any information would be appreciated.
Thanks!
Ken

[RB]

Hi Ken.
I saw that box on ebay.
IMHO...
I would guess it is a line load test box.
Probably used to simulate long line loads.
The jack is probably for a receiver.
My guess would be  , press button 1, can you hear me now?
press button 2, can you hear me now???
That sort of thing.
It should clean up very well.

[Witty]

Thanks RB.
I suspected something along those lines also because of the buttons for switching through the resistors.
I am still curious how it is to be connected to the source.
The S connection appears to be a neutral, or ground?
Not sure how the other two would connect.
Any ideas?
Thanks again for any help.

[Key2871]

ST in central office terms useually means start.
So it may mean to start with that one?
Or in this situation perhaps station?

I once knew an old time telephone guy who used to talk about these, and load coils.
I'm trying to remember what he told me about them, but I think RBs explinaion is the most plauseable.
It just makes sense to simulate a long run or long resistance from the CO to the subscriber to find issue's.

[poplar1]

T R S = Tip Ring Sleeve

[Witty]

T R S = Tip Ring Sleeve

That seems to make sense now. The sleeve is basically the ground and the tip and ring is right and left signals.
The box seems older than that, but I'm not sure when stereo jacks came out.
Thanks Poplar1.
I'll have to do some further research.

[RB]

Ken,
Tip and ring are the line connections.
The third may be a ground???

[Witty]

Ken,
Tip and ring are the line connections.
The third may be a ground???

RB, you are correct.
After a little more research I found that Bell labs were working on binaural signals and the TRS connectors in the early 1900s. I'm thinking WE might have made those 9-A boxes for testing those lines back then but will have to search through more documents. Hopefully I can figure out who made it. The more I read the more interesting it gets.
If anyone happens to run across any documentation please let me know.
Thanks all for your help!
Ken

[Key2871]

With Tip, Ring Sleeve that's for a cord board set up.
But that makes sense. I couldn't get a good inmate of the schematic at first, but then I saw those.

[magicbrain]

Ken,
Here you go - From the 1907 WE catalog - "For Testing Supervisory Relays" - Which I believe were used in switchboards?

[Witty]

Bruce,
That is awesome. I've been looking through the TCI data base files but found nothing yet. It's the exact same one.
I'll post some pics after cleaning it up.
Thanks!
Ken

[Witty]

I got around to cleaning and restoring this unit as close to new as possible. Inside wiring is all intact and contacts all cleaned like new. I did not have to do much internally as all the parts were in excellent condition. Push buttons are all cleaned and buffed back to original condition.
I found the external metal hardware to be corroded over time but found no evidence they were nickel plated, unless they were striped at some time long ago. I polished the brass and refinished the wood enclosure.
I actually like the looks of the polished brass, even though I usually prefer restoring to original condition and nickel plating the hardware if needed.
I've attached some pics before and after.
Now I just need equipment to test it on!

Ken

[Key2871]

I'm impressed, that came out really nice!
Well done, I like to take some thing old and crudy looking and transform it back to what it was supposed to be, and you've done that and did it well. Nice work.

[Witty]

Thanks Ken,
I'm the same way. I've collected old scientific instruments over the years and restored them to original condition, and especially old survey equipment because of my civil engineering background. I got into old phone equipment about 14-15 years ago and wish I had much sooner. I have a lot to learn and am now going through old boxes of phone stuff I acquired back then when I was buying to work on later.
I can do all my own restoration, including plating when needed.
It is so fascinating!

Ken

[RB]

Yes, well done indeed!
The attention to detail is the reward...imho.
I hang my hat on that hook also.
Maybe I am part raccoon???
I just love shiny things!
And that box is a blue ribbon.
Now, Somebody get this guy a 555 board, so he can get the light show going!
"I think a 555 is ok, not certain though...disclaimer inserted here".