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German WWii tabletop LB with LB/CB possibility / Tischfernsprecher 38 or 39?

Started by dsk, January 15, 2022, 06:32:39 AM

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dsk

This telephone was made in 2 different versions, with or without a battery-box with line terminals etc.

I have problems to find any significant difference except for that box, the handset used and  that the one without battery-box has stamped 4.5V on close to the battery terminals.

I have tried to translate the text on the original German circuit diagram, and added some values.

Answers around  the phone related but non circuit related could be posted here: http://www.classicrotaryphones.com/forum/index.php?topic=25826.msg252972#msg252972

The ringer is pretty surprising: 2x 700 ohms coils in parallel. Or maybe not, because that makes a holding coil of 350 ohms, and still a pretty sensitive ringer.

The REN load in CB mode is measured to be approx 4.5

While writing this it popped in a message to clarify the ringer resistance, and the ringer in OB 38 should be around 2500 to 2800 ohms, so I am slightly confused because mine has no text about battery voltage.  Maybe the wartime made it a little more flexible.

With a high ohm ringer the CB mode will not be working so the 39 version might be an improvement in that direction.

The difference between the 38  and 39 version is that the 38 Version uses a standard field telephone handset plugged in, and the battery box with one single 1.5V battery.  The 39 version are more for fixed locations and instead of the battery box it is intended to be a wall box with 4.5V larger batteries. the handset looks pretty similar, but without press to talk button. The higher voltage makes the need of a different transmitter capsule, probably equal to the SB phone of that era. (like those used in W28 etc)



The info I got about the ringers are here:

countryman

Thanks for the diagram. Where did you find it?
The OB/ZB 38 is mentioned in G√ľnther Mergelsberg's standard work "Das Telefon und seine Entwicklung" (1995), but there's no diagram. It is just mentioned that the setup is varying. Apparently versions for manual CB service existed without magneto.
The book is a comprehensive overview of phones in service of German postal administrations. Possibly existing instruments of this type had a civilian use in post-war shortages?

dsk

The diagram is a modified picture of a diagram fixed under a phone.  You may find it here: https://bit.ly/3KdGifo
Mine has obviously been used first by the Norwegian forces (paint), and late by civilians.(line-plug)

dsk

The circuit also use a term SB, that is not a German version of CB!  (CB = ZB here)

SB describes an abandoned system for automatic ring-off on magneto (LB= OB here)the system worked by having a blocking capacitor used in off hook position, and when you went on hook the capacitor was replaced by a DC circuit. (e.g. a low ohm ringer)
approximately reversed thinking of a traditional CB system.
This is the only reason I can see to use such low ohm ringer.

countryman

That is correct. Hookswitch IV/V is wired in a way that it closes a DC loop over the ringer when the respective terminal is used (diagram is drawn on-hook). This "positive ringoff signal" was widely used at least in German LB systems.
What bothers me is that a third capacitor is used in the receiver circuit (C3). What purpose will it serve here? All DC is excluded from the receiver already by C2.
C3 is not existent in the W/OB 35 which otherwise has a similar circuitry:
https://der-fernmelder.de/fernsprecher-feldfernsprecher/w-ob35-tischapparat/

dsk


dsk

Maybe if you have a unit with high ohm ringer, it will not be able to hold the line in CB systems, but if you short out C2 it should work, and C3 protects the receiver from DC.  (Quite strange theory  :)  )

Doug Rose

Dag....here is a Mix & Genest that looks like yours. Went cheap, I had it flagged to bid but got side tracked.   >:( ...Doug

https://www.ebay.com/itm/313801894390?



Kidphone

dsk

If it was a member who got that, it should even do well in the phone of the year.  :) A really scoop. 

Seen from here in a small country it really looks like like Germany and USA has had the leading position in the development of military phones, often in quite different ways, so if we could have put those together ...  The Germans made their extremely practical and high quality equipment in the planning of the war.. The Americans got after but in extreme volumes, and won the war.

When it comes to these phones in this thread, it was not made many of them they were a strange clone of military and civilian design, where I am most fascinated of the circuitry.
After some discussions around this phone on some Facebook groups, understand how rare they are, and how little knowledge that it is about them. It tends to be extremely attractive in some groups where political issues also is a factor, and that makes me wondering about pretty much non technical things. I try to not take political views into my telephone interests.

countryman

German objects from the 1933-45 period seem to have a strange attraction to some people. I suppose if the seller of the above phone had added certain key words, he could easily have multiplied the price. As sad as it is.
The OB/ZB 38 may have had a possible use in offices to maintain and build trunk cables, or in the railway which had it's own mix of LB, CB and automatic lines at that time. But it's existence is more a proof that the Hitler government planned an aggressive war from the beginning on. This type of material was hoarded to be used in occupied country, to quickly make use of intact or partly intact telecommunication structures for own military purposes.
The spelling alphabets shown are an interesting historic detail. The one on eBay shows the official German version after the so called "Arianization". Before 1934 N was Nathan or S Samuel. These and other names were considered Jewish by the nazis, and were replaced. Some of these changes were reverted post-war, but not all. This was discussed lately and is currently in a revision process : https://de.wikipedia.org/wiki/Buchstabiertafel#%C3%9Cberarbeitung_ab_2019
Your phone which had a second life in the Norwegian forces has the international spelling alphabet with a specific pronunciation aid, which is also of historical interest nowadays.