Author Topic: Never seen one like this: STC  (Read 464 times)

Offline dsk

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Never seen one like this: STC
« on: March 03, 2017, 02:26:00 PM »
« Last Edit: March 03, 2017, 03:38:48 PM by dsk »

I have even got a regular New York number :-) 646 570 1796

unbeldi

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Re: Never seen one like this: BTMC
« Reply #1 on: March 03, 2017, 02:37:46 PM »
Why do you say BTMC?
It says Standard Telephone & Cable on the front.

Offline dsk

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Re: Never seen one like this: STC
« Reply #2 on: March 03, 2017, 03:39:53 PM »
Good question, I have changed to STC now

I have even got a regular New York number :-) 646 570 1796

unbeldi

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Re: Never seen one like this: STC
« Reply #3 on: March 07, 2017, 06:07:12 PM »
Is this a railroad telephone ?

Just happened to look at the diagram, and that's what it seems to me.

The set uses a selector system for ringing, driven by the dial of another set.
The circuit arrangement with the transmitter and the receiver each connected to their own winding on the induction coil, working like a transformer with the line on the opposing side, is just like the US dispatcher systems worked.
« Last Edit: March 07, 2017, 06:10:19 PM by unbeldi »

Offline AE_Collector

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Re: Never seen one like this: STC
« Reply #4 on: March 07, 2017, 06:50:00 PM »
Basically, how did the Railroad Selectors work?

My guess is:
A bunch of phones connected to the same 2 wire circuit but potentially huge distances between them. A Selector is in or at each phone with a ringer/annunciator of some sort connected to the output corresponding to the station number for that phone. When someone goes off hook and dials all of the selectors operate and the one in the phone that is actually being called is the only one with a ringer or annunciator connected to that output so only it 'rings". When call is disconnected all selectors return to idle position.

Where is power introduced....at each station?

The selectors must operate reliably on very weak and distorted signals considering the miles of wire?

Terry


unbeldi

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Re: Never seen one like this: STC
« Reply #5 on: March 07, 2017, 07:17:11 PM »
Basically, how did the Railroad Selectors work?

My guess is:
A bunch of phones connected to the same 2 wire circuit but potentially huge distances between them. A Selector is in or at each phone with a ringer/annunciator of some sort connected to the output corresponding to the station number for that phone. When someone goes off hook and dials all of the selectors operate and the one in the phone that is actually being called is the only one with a ringer or annunciator connected to that output so only it 'rings". When call is disconnected all selectors return to idle position.

Where is power introduced....at each station?

The selectors must operate reliably on very weak and distorted signals considering the miles of wire?

Terry



Precisely.

Each station uses local battery power for the transmitter and the bells.  The bell circuit is activated via a relay by the selector that receives pulses from the line. It responds exactly as you suggest, each is essentially a step-by-step switch that is fixed to respond for one code only.

Because the line impedance is very high, the induction coil impedance has to be also very high.  In practice that is several kilohms, and for that reason no single way station presents a very high load on the line, so that all station can even be listening at the same time if necessary.   The high impedance on the line side requires the transmitter and receiver to be isolated by the transformer (induction coil).  Each have their own winding on the IC.

The line side operating voltage for the selector system can be very high, I think in US systems it could be as high as 400 V when the lines were very long and had dozens of stations along the line.  Another reason for good isolation between line side and transmitter/receiver side.


Offline AE_Collector

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Re: Never seen one like this: STC
« Reply #6 on: March 07, 2017, 08:38:34 PM »
Thanks for the description. I have seen many railroad phones over the years as well as the selector switches on eBay occasionally but never thought to investigate (or ask) how it worked.

My turn to learn something new today!

Terry

Offline dsk

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Re: Never seen one like this: STC
« Reply #7 on: March 08, 2017, 02:43:54 AM »
I should have mentioned, this phone is not mine, the ad: https://m.finn.no/bap/forsale/ad.html?finnkode=90400437
I am pretty sure about this system has never been used in Norway, but it is an interesting phone.  Here they used magneto telephones with high ohm ringers until they got regular phones.

Still this is an interesting solution.

As you see it is for sale for NOK 2000 (close to $235)

Far more than I like.

dsk

I have even got a regular New York number :-) 646 570 1796

unbeldi

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Re: Never seen one like this: STC
« Reply #8 on: March 08, 2017, 10:33:11 AM »
Sam Hellas has a page for British railway telephone systems on the web and he also covers the STC systems. I learned that STC licensed the Western Electric selector system, and I found several documents for the 4000-series equipment of the 1950s, but I have not found anything about this 3000-series set.

Are there any collector's sites for railway systems in Scandinavia ?


Offline dsk

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Re: Never seen one like this: STC
« Reply #9 on: March 08, 2017, 11:32:19 AM »
https://www.njk.no/

Not much help.

I have even got a regular New York number :-) 646 570 1796