Bell Antwerp (BTMC) AD51879 railway telephone

[Matilo Telephones]

Picked up this unusual piece of railway telephony last weekend.
I found it in an on line auction on Catawiki and the design of the housing drew my attention. It was made by BTMC (Bell Telephone Manufacturing Company) in Antwerp, in the 1950s. Having never seen this design before, I bought it out of curiousity (and because I could pick it up semi-locally).

It turns out it was part of a railway signalling system and used by the Nederlandse Spoorwegen (Dutch national railways).

The big glas part inside is a Western Electric Type 60 selector, possibly licence built in the UK by STC.
Here is a page by Sam Hallas on this subject:

http://www.samhallas.co.uk/railway/stc_control.htm

The sign at the front reads:

Central Switching Station Zwolle
To call CSP (probably Central Switching station)
1 Listen if the line is free
2 state your name and location
3 wait for the CSP to respond

If the line is not free, hang up the phone and listen again later

call for the station:
A the bell rings and the plate falls
B pick up the phone and respond

All in all the phone is in great condition: paint is still very good (a few chips), no rust, Bakelite nice deep black & shiny, electronics original not it seems as nobody has messed with it. Even the cord is still good.
This is a kind of Phone you do not see every day! :-)

[unbeldi]

What a great find.  Love it.
It would be fun to make it operational again, but you still need a selector key, which seem even harder to find.  But as a substitute the pulses could probably more easily be produced with a microprocessor and relay. Be prepared for high-voltage work! (for the selector)

I would be very interested in measurements of the induction coil. 

[unbeldi]

Have you found any documents for this model?  I would date this to the late 1940s to mid-50s.
Are there any dates on the unit?

Railroad technology was pretty constant for decades, only the style and material details changed slightly.

[Matilo Telephones]

I have not found any additional documents on it. Mine was made in 1952 (capacitor date).

I did find an other one for sale, in a section for railroad collectors and it was called a selector Phone (Selektor telefoon).

I may try to connect it to a normal line and see if it can function as a CB-telephone, although I guess it will not ring without extensive modifications.

[dsk]

Couldn't hurt to give it a try?  If you connect the pots line to red and green, and put in a 1 uF capacitor on the selector terminals 1 and 2 something may happen when you call in.

dsk

[unbeldi]

I have not found any additional documents on it. Mine was made in 1952 (capacitor date).

I did find an other one for sale, in a section for railroad collectors and it was called a selector Phone (Selektor telefoon).

I may try to connect it to a normal line and see if it can function as a CB-telephone, although I guess it will not ring without extensive modifications.

I think you should get the second one too, and make them work together as intended.

Many railway systems used very high impedance hybrids to present a very low AC load to the long lines, which could be hundreds of miles long and have dozens of way stations connected all the time (no hook switch on the line side usually). For example the No. 42 coils in Western Electric systems used about a pound of copper wire and I have measured their impedance to over 10,000 ohms at 1 kHz frequency.

The name "selector phone" makes sense of course, it has a selector in it.  The counter piece to address the selector would be a selector key set. These are desk-top boxes with a lever for each digit to select the number to be called. The selectors are fixed internally to connect the ringer to the line only when the specific code is sent down the line in form of DC pulses, much like a step-by-step system.  Since BTMC used a Western Electric selector, you might be able to use one of their keys as well if a BTMC type cannot be found.

[unbeldi]

Couldn't hurt to give it a try?  If you connect the pots line to red and green, and put in a 1 uF capacitor on the selector terminals 1 and 2 something may happen when you call in.

dsk

I rather doubt that would be very effective.  The instrument has separate coils for the receiving and sending side, they do not function like a normal transformer hybrid, do not share a common core.  So just making the transmitter work, does not get you very far.  Of course one can hook up a ringing bridge to the line directly, which is what your drawing does.

[Matilo Telephones]

I think you should get the second one too, and make them work together as intended.

I don't think my wife agrees with you. :-)

[unbeldi]

I think you should get the second one too, and make them work together as intended.

I don't think my wife agrees with you. :-)

Hmm, put a wreath of season's flowers around it and some scent, and second one in the basement.

[dsk]

Couldn't hurt to give it a try?  If you connect the pots line to red and green, and put in a 1 uF capacitor on the selector terminals 1 and 2 something may happen when you call in.

dsk

I rather doubt that would be very effective.  The instrument has separate coils for the receiving and sending side, they do not function like a normal transformer hybrid, do not share a common core.  So just making the transmitter work, does not get you very far.  Of course one can hook up a ringing bridge to the line directly, which is what your drawing does.

We are talking about using a phone in a different way than it is built for, and without irreversible or heavy modifications.  This should be easy to test, and I believe it will be working better then a hybrid made of resistors. Not perfect, but good enough for having a little fun.

dsk

[unbeldi]

The ringer in these phones is a low-voltage DC ringer, powered by the same battery that is used to power the transmitter. It was not driven by a ringing signal over the line.   The selector activated the bell circuit.

To make it work for an actual conversation, you have to completely replace the internals, or use another set like it.
The unit has two separate isolation transformers for the receiver and the transmitter, so just hooking up the set as shown, does not work.

[Matilo Telephones]

Well, I did as you suggested, Dag.

See pic.

I got dialtone, but it does not ring. Receiver is quite faint, but it may be faulty. Transmitting is fine.

I did notice there was a separate battery mentioned on the diagram, Unbeldi.

I thought perhaps there is enough room to fit a loose bell unit in there. That way I can make a conversion that is easily reversable.

[unbeldi]

Yes, the transmitter will work, that only requires a DC source, and not necessarily an induction coil, as a series system.
The transmitter is faint because there is virtually no inductive coupling between the circuits. You would have to wired the receiver also in series with the transmitter, but then you're sending DC current through it too, which could magnetize or demagnetize it over time.

If you want to hear the phone ringing use a lantern battery of 4.5 or 6 volts and connect it directly to the ringer terminals.

[dsk]

I like playing around and sometimes my odd solutions works.
I made a new suggestion using the battery mentioned, for ringer.  adding a relay for ringing (high ohm and capacitor) removing a link and connecting line a little different. Removing the handset receiver wire, putting in a capacitor 1-5 uF. This circuit will then be pretty equal to a Kellogg phone with a 1 winding coil. The Hence will still be to get the original indicator, and ringer in action, and an acceptable voice circuit. (no anti sidetone)

dsk

[unbeldi]

Are you trying to better Beethoven?

I have to state, that I am a sharp critic of such experiments, "playing around".  Doing it by oneself in private to learn is one thing, promoting it in public is another.  These instruments were for the time highly developed, finely tuned technology, and worked just perfectly in conditions or situation that were technically very challenging. IMHO, it is often quite a bit of a challenge to make them work today the way they were intended to work even without challenging conditions, such as 100 miles of copper wire, ground shorts from wind, ice, and rain.  For example, how many collectors do you know who actually built a properly functioning party line with their phones, whether it is used frequency ringing, polarized ringing, or anything else more sophisticated than a dry magneto line?
Most here probably know exactly how to cobble together a somewhat working telephone from spare parts, working at least under the exact condition during the experiment.... a handset, an induction coil, or even just a resistor and and a capacitor. That's a nice little exercise.  But I don't need to tear into a nice, complete instruments like this to confirm that.  We know how a handset sounds and speaks.  Connecting a battery to the ringer for a test is nice exercise, because ringers don't all sound alike.
But starting to insert components into this circuit to somehow try to get sounds in and out of this box cannot duplicate the experience of authentic operation and one can achieve that by disconnecting the handset set and hooking it up to a working modern phone.  There is even enough room in that box to put a 101A induction coil between the line and the handset. But what is the point of that?

Ok,  this is why I suggested to buy the second phone, a second phone is needed to demonstrate this technology, at least the speaking part.  Signaling is still another story.