Linking magneto party line phones together as intercom

[JesseCake]

Hi folks,

I found your excellent forum whilst searching for an answer on Google.

I'v done many things with phones over the years, however mostly I've planted my own microcontrollers on the inside, and had them count pulses to action different things (run robotics, switch lights, play sound effects into the earpiece etc) and now I'm looking to link several "party line" phones together (the type with magneto cranks on the front) to form an intercom between outdoor sheds and workshops as well as the house, with the cranks on the front able to make all of the other handsets ring.

In the past I've been able to link together standard phones by putting a 9V battery, 300 ohm resistor inline with either L1 or L2 on a standard 2 wire phone setup which allows simple talking between two phones. But I think that this might be for more modern phones that just have a simple need for L1 and L2 to be hooked up, as well as without a need to ring the other handset.

I now have an PMG 334 MT (I think it's an Australian phone based on an Ericsson from the 1940s or so?) with hand crank magneto instead of dial, and so far I've been able to get it actively ringing another nearby phone (another older dial based bakelite phone) by hooking up L1 and L2 to the corresponding lines on the opposite phone. This is all fine. The problem I then faced is that I realised this party line phone (334 MT) seems to require a separate battery line rather than simply feeding the power through the two main lines according to the schematic on the inside of the phone which I've also correlated with online diagrams (which also showed me I needed to hook up the bells in a certain way also). This is fine, and I did so with the above mentioned 300ohm resistor and 9v battery, which got the transmitter running. So far so good!

My first question is, is there a way of wiring these party line phones so that I can continue to supply a single power source that feeds their transmitters, or do I have to have a battery at each separate phone? This isn't a show stopper if I need a little battery behind each phone, it'd just be handy to have a central power source is all.

My second question is, when hooking more than two together, should they be connected in parallel with a chunky centre point connecting the L1s to each other, and the L2s to each other, or should they be strung in series with each other (L1 to L2 of next phone in large circle)?

I realise this may be something simple for you phone pro's, but I'm only starting out - any help is very welcome and thanks in advance,

Jesse Stevens

[JesseCake]

Hi folks,

I found your excellent forum whilst searching for an answer on Google.

I've done many things with phones over the years, however mostly I've planted my own microcontrollers on the inside, and had them count pulses to action different things (run robotics, switch lights, play sound effects into the earpiece etc) and now I'm looking to link several "party line" phones together (the type with magneto cranks on the front) to form an intercom between outdoor sheds and workshops as well as the house, with the cranks on the front able to make all of the other handsets ring.

In the past I've been able to link together standard phones by putting a 9V battery, 300 ohm resistor inline with either L1 or L2 on a standard 2 wire phone setup which allows simple talking between two phones. But I think that this might be for more modern phones that just have a simple need for L1 and L2 to be hooked up, as well as without a need to ring the other handset.

I now have an PMG 334 MT (I think it's an Australian phone based on an Ericsson from the 1940s or so?) with hand crank magneto instead of dial, and so far I've been able to get it actively ringing another nearby phone (another older dial based bakelite phone) by hooking up L1 and L2 to the corresponding lines on the opposite phone. This is all fine. The problem I then faced is that I realised this party line phone (334 MT) seems to require a separate battery line rather than simply feeding the power through the two main lines according to the schematic on the inside of the phone which I've also correlated with online diagrams (which also showed me I needed to hook up the bells in a certain way also). This is fine, and I did so with the above mentioned 300ohm resistor and 9v battery, which got the transmitter running. So far so good!

My first question is, is there a way of wiring these party line phones so that I can continue to supply a single power source that feeds their transmitters, or do I have to have a battery at each separate phone? This isn't a show stopper if I need a little battery behind each phone, it'd just be handy to have a central power source is all.

My second question is, when hooking more than two together, should they be connected in parallel with a chunky centre point connecting the L1s to each other, and the L2s to each other, or should they be strung in series with each other (L1 to L2 of next phone in large circle)?

Let me know if you need more information or images.

I realise this may be something simple for you phone pro's, but I'm only starting out - any help is very welcome and thanks in advance,

Jesse Stevens

[poplar1]

You can use a single power source for talk battery, but then you would have to run a second pair between phones to carry this power.

Originally, phones on the same party line were connected in series, using one wire (line) with ground (earth) return. However, this requires ringers of very low resistance since when on hook (idle) each ringer is in series with the other phones that are on the line. In other words, the talk path is through the ringers of other phones on the line. The "metallic" line (using 2 line wires rather than one line + ground) was discovered by accident, but proved superior to the former method.

[poplar1]

You don't need a "chunky centre point" to connect them in parallel. Just extend L1 and L2 from the first phone to L1 and L2 of the second phone, then from 2nd phond to 3rd, etc. Some party lines had 20 or more phones connected in parallel over a distance of 20 miles.

[dsk]

Hi, and welcome to the forum.
When you connect the L1 and 2 from one to the other phone you should be able to ring in both directions.   The 2 telephones will need a 3V battery each for powering the transmitter.
You may put a great number of phones on the same line, but you need a battery to each.   If you are connecting many phones they should have pretty equal ringer impedance, if they are not equal, those with lo impedance should be located in the ends of the system.

dsk

[TelePlay]

Jesse,

Welcome to the forum.

I moved your post here from another board and then merged the post (seems identical) from the intercom board. This will allows members to reply in one place to help you connect the phones.

As always, pictures help.

[Jack Ryan]

My first question is, is there a way of wiring these party line phones so that I can continue to supply a single power source that feeds their transmitters, or do I have to have a battery at each separate phone? This isn't a show stopper if I need a little battery behind each phone, it'd just be handy to have a central power source is all.

If you had several Tele 334MT telephones you could use a central battery and an additional wire (a total of three wires) to each telephone. If you have a mix of telephones, that might not be possible - not all local battery telephones use the same compatible wiring.

Personally, I would use local batteries. It is simple, all the phones would then be compatible with each other and if there is a battery fault, only one phone is affected.

My second question is, when hooking more than two together, should they be connected in parallel with a chunky centre point connecting the L1s to each other, and the L2s to each other, or should they be strung in series with each other (L1 to L2 of next phone in large circle)?

The phones would be connected in parallel - L1 to L1 and L2 to L2. If the phones are any distance apart, you can save wire by using a single wire to connect all the (say) L1s together and connect all the L2s to ground. Make sure you join the wires properly (solder them) or you will end up hearing the local AM radio stations better than your correspondent.

(Phones used to be connected in series but that was about a hundred years ago. The 334 and its contemporaries are designed for parallel connection).

Regards
Jack

[Jim Stettler]

Ralph Meyer addresses DIY intercoms  in his book. "Old time Telephones"
  https://www.amazon.com/Old-Time-Telephones-Technology-Restoration-Repair/dp/0070418187

ISTR that he used audio isolation transformer to couple the phones to the line.


Jim S.

[Victor Laszlo]

The original telephones were called "local battery" sets.  Each telephone had its own battery supply to power the transmitter. The telephones were connected in parallel across a dry (unpowered) pair of wires.  The phones' talking circuitry and their ringers are capacitively coupled to the pair.  You lift the receiver, and turn the crank. So-called "off-normal" contacts on the shaft of the magneto close, allowing the ringing current from the magneto to make a metallic connection to the line. All the other magnetos are off-line. All the ringers are connected to the line, via capacitors.

The switch hook contacts close when you take the receiver down, and that action powers the transmitter. When you hang up the receiver, those contacts open, preserving the battery.

So, to make your local battery sets work reliably and prototypically, each one will need its own battery supply, and you must ensure that they are wired and installed according to this scheme.  I'm sure that if you were to Google "local battery telephone" you will find a plethora of info, with diagrams.  Good Luck!

[poplar1]

All the ringers are connected to the line, via capacitors.

The WE 1317 and other local battery sets did not require a capacitor for the ringer. Some were equipped with capacitors, but these were in the receiver circuit, for those lines where some subscribers forgot to return the receiver to the hook (after eavesdropping?). The capacitor allowed the phones to ring even with one or more receivers off hook; otherwise, the lower resistance of the receiver when compared with the ringers would prevent ringing.