Danish Phone Find

[dsk]

upps - did not realise that a reply was allready posted :-)

Thank you for that additional info, and the nice catalogue.
dsk

[Jack Ryan]

As a "Rule of Thumb", most of the time when a discreet button is on an old phone it is there to provide  a momentary ground reference .
Jim

Jim,

That rule of thumb only applies for CB telephones. On an LB telephone, a ground usually has no effect.

Jack

[countryman]

Thanks for the responses, and the document linked!
In fact one of the closing contacts shorts the induction coil, like the mentioned "Lauthörtaste" on a German OB05.
I still have to investigate upon the second closing contact - though the function of the phone is simple enough, understanding how it's wired is not 
When cranking the magneto with the handset on hook, the bell won't ring anyway, and the voltage between L1/L2 easily exceeds 100V. That should be enough to call a remote office!
With the handset off hook, the bell rings and the voltage is somewhat lower. Pressing the button when cranking mutes the bell by shorting  it out and the magneto as well. I don't think this is an intended function.
The phone has a 5 wire mounting cord. "EK" and "L2" are connected inside the plug.
As far as I understand L1 and L2 are the line wires, Z (battery zinc contact) and K (coal carbon contact) are - and + of the mic supply. But what is EK?

The pics show the 2 closing contacts, both operated by the single button, the hookswitch, the terminals in the phone, and the plug which is an older version of the one posted by DSK, also with the "J" (Jord, ground) contact unused.
The 4-prong plug in the first pic connects the handset to the phone. It is seen frequently on this type.

[Jack Ryan]

Here we have some different traditions on magneto phones depending on the countries or even telco's standards.  Pretty often magneto telephones in the Scandinavian countries had a button for "bad lines" when you hold that button in, you shorted the induction coil, and the receiver was the only part across the line, in on-hook position, the button disconnected the ringer, and all the energy from the magneto-generator was sent out on the line.  I do knot know if that was on this phone pictured, but here in Norway that button was standard until anti sidetone came on magneto telephones.
dsk

That type of phone is not usual here (Australia but also the UK and US) but they are used in noisy environments. As you say the transmitter is disabled so that local noise in not transmitter to the other party but more importantly, does not cause a loud sidetone masking the other party.

Another reason magneto telephones have a button applies to party lines. For example:

1. Pressing the button while cranking the magneto can be used to send a party code.

2. Pressing the button while cranking the magneto can be used to signal the operator rather than another party line subscriber.

If the phone posted was used by JYDSK, I suspect the button disconnected the bells while cranking. Some KTAS telephones used a button for party line use.

Jack

[Jack Ryan]

As far as I understand L1 and L2 are the line wires, Z (battery zinc contact) and K (coal contact) are - and + of the mic supply. But what is EK?

In English, K means carbon but what you say is correct. EK is the bell wire which is normally connected to L2. It could be connected to ground for selective party line ringing or an extension bell could be connected between L2 and EK to put the bells in series.

Jack

[countryman]

I now separated L2 and EK in the plug. The ringing voltage now only is on EK. When depressing the button, it also is on L2.
So the button, as you stated earlier, may be used to send the ring voltage in a differnet way, e.g. on party lines provided the system is wired so. Thanks for your thoughts, they really helped me to understand how this phone is set up.

By the way, the phone does not tell anything about it's age on the inside. No marks, stamps, dates at all. I guess "around 1920" is the closest I can date it.

[ma_xyz]

i remembered to have seen some day a diagram of a danish phone of that type, found it again after some googling: http://museum.vintageelectronics.nl/Telephone/KTAS%20-%20M1920/Kjøbenhavns%20telefon%20aktieselskab%20-%20M1920,%20strømskema.pdf

this diagram shows only one contact on the button, but perhaps still helpful

(i believe the text says that if installing it on a party lin then remove connection A and switch label to show the text)

[Jack Ryan]

(i believe the text says that if installing it on a party lin then remove connection A and switch label to show the text)

Yes, that one is for party line. The text on the reverse side of the label says to check the line is not busy before making a call.

Jack

[dsk]

May this be understandable?

[countryman]

Thanks DSK, this makes clear that they were frequently used on party lines. My set has the tiny screws for the label but there is none attached. Obviously it was on a single subscriber line.

[Jack Ryan]

Thanks DSK, this makes clear that they were frequently used on party lines. My set has the tiny screws for the label but there is none attached. Obviously it was on a single subscriber line.

Actually the label was always fitted and is double sided. By default, the label shows KTAS. It is reversed when used on a party line and then says "check the line before calling" (or thereabouts). If it is missing, someone probably wanted it elsewhere.

Jack

[Key2871]

 :Well I've never seen the innards of one of those sets..
Thanks for the good pictures!