A simple intercom from a pair of old wired phones

Do you have a couple of old telephones in your pantry? - No need to throw them away - make a very simple intercom from them - an intercom. With it, you can establish a wired connection to hundreds and even thousands of meters. All for free and no roaming.
At one time, with a friend, we installed such an intercom between apartments, and wires were passed through the windows. And now it has not lost its relevance: you can establish a permanent connection with a summer house in the garden, with a bathhouse, with a neighboring house, etc. It is also a great toy for children.

Will need

• Two telephones - any: push-button, disk, the oldest Soviet or the newest foreign.
• Wires for connecting phones to each other. If the device is connected through a socket, the wires should be with connectors on the end.
• Battery 9 V type "crown".
• 300 ohm resistor (+/- 10% if not exactly that).
• Insulating tape or heat shrink.

Tool:

How to connect phones and make an intercom - intercom

Everything to the point of banality is very simple! You just need to connect all the elements in series: telephones, battery, resistor. Polarity is not important.
For reference: The usual modes of the telephone network are such that at the moment of rest, the network has a voltage of 60 V, at the time of a call - 180 V and at the time of conversation about 9 V. Here we are using a battery to create a potential of 9 V. in the circuit between the devices.
Take the wire connecting the phones and cut one of the two and make a branch.
In the gap, turn on the resistor and battery. All! The intercom is ready.
We check. If all is well, solder everything to a constant and isolate with heat shrink.
Further, it is desirable to place everything in the housing. After making a slot in it under the wires.
As a result, the intercom has the form:
Check the work:
Audibility is excellent: clear, without jumps and "failures", in general, ideal.
Now you can extend the wire at any distance. It is not necessary to disconnect the battery - if both tubes are lying down - the current consumption is almost zero.
But if you don’t have a crown, take a regular 9 V adapter.
Or 12-15 V, but in this case you will need to make a buck converter according to the scheme:
We assemble and isolate with heat shrink.
Now, if you need to make a conversation with a subscriber, plug the unit into the network and talk.