My German WWii field exchange

[dsk]

Now it is close to complete. Only missing the transport cover to the trunk unit.
This is the field exchange used by the Germans during WWii, and by the Norwegian forces after the war.

It has several similarities to the TA-SB22/PT, at least when you use the SB222 with external telephone instead of the operators pack.

Now I got my trunk unit, and the setup is complete.     
Here at my kitchen table.

dsk

[dsk]

You may see the Norwegian manual here: https://www.scribd.com/doc/44095368/X-Tysk-Feltveksler-SB10T
An interesting documentation of German telephone related stuff here (not mine):  http://tinyurl.com/h9d9v95

dsk

[19and41]

That switchboard looks nicer than the austere can that the SB-22 was.  Ours had no provision for direct operation in a rotary dial network.  That is a nice display you have. 

[dsk]

When I served in the Coast artillery, we used officially the SB22, but we did have on of those pictured over in service too.

The SB22 had a dialpad add-on, but here we were considerably slower with DTMF. The fortress got automatic exchange in 1983, a used one, and rotary only!   

As late as 1975, our "Televerket"   (The Norwegian Ma Bell) started experimenting with telephones with buttons, and in 82 the first std telephone with buttons came.  2 different series, 1 with pulse, and one with DTMF, just to cover all types of exchanges. The layout was calculator, not phone std. 

Back to the ex-German exchange.  It is still extremely reliable, and not as heavy as the SB22, but not modular.  The Germans uses and used slightly different standards from what we do in the rest of the world. The ringing voltage is as low as 60V, and the indicators coil has only 600 ohms resistance. (The same as telephone ringers had in Germany up to maybe 1970) This caused a to high REN load to have the trunk in parallel with another phone.  In addition they had some exchanges connecting one of the wires to ground when the dial was out of rest position. (The only use for the ground/Earth terminal) . They also had some LB exchanges where the automatic ring off detection detected current between ring and tip.  You had to ring up the exchange by cranking the inductor, and have a capacitor in the circuit when speaking. When going on hook, the capacitor was bypassed, and the dc current gave the end of conversation signal.
For me, this is a pretty strange way to solve it, but that are probably related to CB thinking.

dsk

[dsk]

Circuit translated:

[dsk]

It is also made another trunk possibility, a CB telephone with jacks for the cord board. https://goo.gl/MA29SP

[dsk]

I have to admit that the 1933 design of trunks does not fit the design of an modern IP telephone adapter, the REN load is to high.  (xLink copes with it)
an extra 1 uF capacitor in series with the ringer/signal device solves that. 
Even when Europeans has kept on rotary telephones far longer than in North America, you will probably need some sort of pulse to tone converter. (again xLink copes with that too)

(The same does actually be true for the newer German field exchange from the 70'ies)

dsk