I know exactly what’s inside that shellac varnished wooden phone - a ringing magneto with large horseshoe magnets generating about 100v AC, frequency determined by cranking speed for the ringing current, capacitors to separate the ringing AC and speech DC currents, and what’s called an “anti side tone induction coil” to control the volume of the speech signal. The bells have a rocking armature and a striker to hit the gongs. There will be a battery box with a couple of large dry cell batteries for the speech current somewhere nearby, the speech signal is carried by 3v DC from the batteries. There will also be a push button for sending a dot-dash bell code while hand cranking the magneto.The receiver, an iron diaphragm controlled by an electromagnet, is hung on the side of the box on a “gravity switch” that connects the ringing current to the line when hung up and the speech current when off the switch, and disconnects the battery when hung up. The transmitter, a microphone filled with carbon granules, is on the front of the phone under the bells.
The phone line out is the overhead on one side and the rails on the other. Many primitive phone systems use a single wire with earth return, obtained with long earthing stakes driven into the ground, signal quality varied with the conductivity of the soil. A similar single wire-earth return was used on some country branchlines in NSW to operate electric train staff machines. If the soil was dry and conductivity so poor the staff machines would not release a staff for a train, it was recommended that someone piss on the ground around the earthing stakes (urine is full of useful electrolytes) to reduce the resistance - it usually worked.
I worked on phones like that, and the metal case mining phones that used to be mounted on or near railway signals, best job I had on NSW railways. Now an obsolete skill, like the phones and similar devices it maintained and restored are obsolete.
The old Telephone Workshop at Redfern, like all the workshops around Eveleigh and Redfern, were a great place to make or get made foreign orders like custom motorcycle parts, and there were electroplaters who’d do a great job chroming or nickelling small bike parts too.
All that and a two schooner lunch at the Glengarry Castle Hotel.
A big contrast to the shithole of misery the job has become in more recent years.
> On 11 Jun 2021, at 10:06 am, Mal Rowe mal.rowe@...> wrote:
> On 10/06/2021 17:19, Tony Galloway wrote:
>> It’s the telephone connection to the winding house.
> 7 minutes - typical fast response!
> Yes, it was for a telephone connection to the engine house.
> If you look at the pic (at: https://tdu.to/i/78320) you can see the telephone above the driver's right shoulder.
> The system now uses 'induction loop radios' according to Wikipedia, but the trolley poles are retained as historic artifacts.
> Mal Rowe - who only noticed the telephone when he scanned the old slide yesterday.
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