DIY trunk unit for cord board or field exchange (Amtsanschließer)

[dsk]

During some of my last projects, I have been asked how to make a suitable trunk for a field exchange.
SB22 has a std. trunk line, but you need a special dial unit for that one.
The German WWii field exchange has at least 2 different kinds of Trunks called Amtsanschließer and Amtsusaz. these are pretty rare, and (looks unrealistic) expensive (by my opinion) For the moment it is one Amtsanschließer for $1300 ++

OK we make a little box witch will together with a normal phone do what the Amtsanschließer do. And now we may even use touch tone.

Not everybody is sturdy on wiring diagrams and components so I made a double schematics.
This German corboard does not use 6.3 mm (1/4"), the plugs are slightly longer, but it works.

dsk

[RB]

Interesting. So this little ditty will be a trunk for the head end of a CB switchboard?

[dsk]

Both the SB22 and the German trunks uses only capacitors to isolate between the magneto lines and the CB lines. (More modern trunks may use a 1:1 voice frequency transformer) But I go for the simple and well proven solution.

The jack contains a little switch and when you have answered, or called out with your regular telephone you plug in the cord, and the switch disconnects the phone, and put in the holding coil to bridge the line.  That is why the coil has to have a suitable dc resistance, and at same time not should steal all the voice signals. 

The local battery user has to remember to ring off so the operator may disconnect when they are finished. (Exactly as the do with the ordinary equipment.)

dsk

[dsk]

Had aloast forgotten this, but now I just found the unit I made.
It is inspired by the German WWii solution. The jack is under the handset, but still when something is plugged in you are not able to listen, talk or dial, it is just a trunk.   And ofcourse it may dial pulse or tone

This was replaced by an US dialpad for a field telephone on my VOIP line, and a rotary dial to the old pax that does not understand tone signals.

More about that in this thread: http://www.classicrotaryphones.com/forum/index.php?topic=23149.msg247003#msg247003