Norwegian: Elektrisk Bureau 1967

[dsk]

If you did want a wall telephone this was the only solution. (picture from add)
Add: https://www.finn.no/bap/forsale/ad.html?finnkode=190446772
The wall mounted shelf designed for this phone standing in the back of the picture.
dsk

[dsk]

Today I got one with DTMF, a pilot serie never used commercial but a part of the developmen tof the later "tastafon"
From earlier I had a dial with pulse electronics just to compare.

[RB]

Wow! that's a busy board!

[dsk]

Got more diagrams form a fellow collector, not sure that I understand all them:

[dsk]

And more:

[dsk]

...and even more:

[RB]

In pic #3, that DF320, is that how they are producing the tones?
I once saw an Analog arcade monitor...TOTALLY Analog!
The board was ALL transistors. ARG!!!
I could not follow that thing for nuthin!

[dsk]

You may even use these pretty easy as intercoms, by putting up a battery in series with 2 phones and adding a Zener diode with a voltage slightly higher than the half of the battery voltage it will work. e.g. a 48V battery and a zener of 26V, put it all in series and be sure of that you have the right polarity of the phones.

If you reduce to 24V and a suitable zener voltage 13V ish? you may need to use the dial to get enough power trough . If you charge the battery at a higher voltage, the phones may beep, so maybe slightly higher voltage in the Zener?