OB - Einsatz

zum N- und O-Gerät

Manufacturer Gema

Status: 14 September 2015

2 News on the 'Lichtzeiger' (light-beam-marker) projection!


Viewing our recently obtained OB - Einsatz

Also known as 'Sichtgerät'


On the left-hand side we see the OB module

Photo derived from a genuine Seetakt manual

On the right-hand side we notice the range measuring module, also known as Messkette OK

The purpose of this display unit was to measure range, it could, however, also been plugged into an another frame:


Viewing the OB module now in conjunction to Freya (Seetakt) receiver frame (N-Gerät)

In both cases being employed for the same purpose - controlling range accurately. 

Please consider also the application of this module within the Mammut radar system.


Viewing the OB - Einsatz from its front side


Noticing the right-hand side of the OB display module


Shown is the right-hand back side


Looking it from the left-hand back side

The circular hole is constituting the dual-beam CRT base (socket)


Facing it from the left-hand side


Viewing it from the left-hand front side

Never noticed before, also never read about it - is the mechanism in front of the display unit


Looking at it a bit more close

Through the hole a key-like instrument should be inserted and then being rotated (quasi winding the mechanism up)

The handle on the left-hand side is to unlock the CRT base-holder. Without pushing it anti-clockwise the CR tube cannot be pulled out fully.



Viewing the mechanism from the opposite side

Please notice also that the lens holding frame being pulled downwards; both lenses missing in our case

Just popping up in my mind - the left-hand side (rusty) handle being kept locked until the mains switch being set in its - off - position? Which would have made sense - preventing hazards.

Why not reproducing its genuine schematic when it is available?


Maybe not well visible on the far right-hand side, the arm carrying the short-cutting device is also connected onto a vertically mounted rotary switch. The switching provision marked '309' constitutes the mains on-off, and '319' meant for loading by means of a 'bleeder' circuiting the HT separately

(source genuine manual Fu. M.G. (See takt) 40G (gB)

Consequently, our display module being currently set in the off mode; because the 'HT bleeder' being connected onto ground.


Please notice the broad slit in the front part of the mu-metal CRT screening tube

I guess, that hardly one of you knows where it once was being meant for.

Please notice also the 'in the air hanging two wires' and contact-strip, as well as the signs of metal deformation.

In my perception - the two wires were once providing the projection-lamp current ('Sofitte' or tube-lamp, regularly supplied in a 5 W and 10 W version). Such lamps were until quite recently used in cares for interior illumination.

To those not trusting the previous information:

Please notice the genuine Fu. M.G. (See takt) 40 G (gB) manual text:

Genuine reference text:    ..... Um bei Betrachtung des Schirmbildes Paralaxfehler auszuschließen, wird die Nullmarke von hinten auf den Leuchtschirm des Braunschen Rohres projiziert, in dem ein enger Spalt von einer Sofittenlampe* beleuchtet wird. Das durchtretende Licht erzeugt mit Hilfe einer Optik auf dem Leuchtschirm (phosphorous layer, AOB) ein Bild, das durch Schwenken des Spaltes und durch verschieben der Optik scharf eingestellt werden kann. .....



Soffittenlampe C5W 12V 5W

Photo copied from: http://www.ersatzteilbox.com/product_info.php/info/p67429_Soffittenlampe-C5W-12V-5W.html     These lamp types being still available and were (are?) widely used in cars for all kind of purposes. Its advantage, is, that the filament shining being stretched and therefore is illuminating in a broader way. 


For a more comprehensive understanding of what it all is about -

We have to copy some of our Mammut-Wassermann page

For it we view at a drawing to AEG's patent application


 This revolutionary patent DE891577 CRT concept is, in my perception really clever

It was thus meant for projecting at the rear (vacuum) side of the phosphorous screen layer a marker line. For example shown in the next drawing. By the way, this display equals the once we recently have obtained and being discussed on this webpage.


The vertical red line at the CRT screen symbolises such a reference line

The advantage - such a reference is not being generated by electronics; hence, not victim to aging and other instability nuisances.


  For us sadly - the projection provision is lacking

Please notice the two screw on the left-hand frame, next photos will show to us, that there existed a frame construction upon which the light projection system rested.

I was told that my friend once got it from England, most likely formerly owned by late Graham Winbolt.

Please consider our current Jagdschloss setup (of course, reflecting only the modules we possess)



Please notice, that since 10 October 2016 we possess an operational projection facility by our own!

On 13/14 September 2015


Frank Müller very kindly did sent us a bunch of photos unrevealing how the light projection system does look like.

Frank possesses a comprehensive collection on German naval (KM) communication gear. His nickname is therefore "Marine Müller".


Sof. 15 is the housing to the projector light source. Above described consisting of a Sofitten Lampe

(courtesy Frank Müller)

Please consider the zinc-colour or Al like axis on the left-hand side. It looks like that the light-source housing can be tilted side wards to the left-hand side.

The adjustable means is looking quite rusty.


The cylindrical hole construction pointing into the mu-metal screening cylinder contains the optics

(courtesy Frank Müller)

Please notice the rusty 'Stellschraube'; which might move the 'light-beam or slit' a bit more to the left or right. To what I understand, the projected vertical light-line (reference) should be visible at about the centre of the CRT screen. Another option, is, that it might fine adjust the main light rays generated by means of a Sofittenlampe.  

I don't know yet, whether the light-slit being integrated inside the Sofitten light source housing or is integrated into the optical projection system; at an approximate angle of 30 degrees towards the phosphorous CRT screen layer.

I must admit, that I have never encountered such a construction before.


Does this photo imply - that the optical system does not 'dig' into the mu-metal screening slit area?

(courtesy Frank Müller)

This might imply that the optical system being small; I mean its optical system cylinder length. 


The locked-screw in front might be meant for tilting the Sofittenlamp holder (housing)

(courtesy Frank Müller)

I cannot see clearly where the axis face to the front panel is going to. Maybe somewhere accessible from the front section. After having looked closely at a previous photo, it becomes clear that inside this rusty shaft there must exist a loading spring. Hence, this spring-load pushes at the axis centre. Is this providing a rotation against the CRT centre axis?


Maybe a bit more conclusive picture, we can see how the projection lamp holder can be tilted up or down as to adjust the light-slit against the CRT screen centre. It also shows how the lamp holder can be rotated (brought) in a vertical position. Likely for changing the Sofitten lamp. 


This provision might make clear wherefore the loaded spring in front being meant for

(courtesy Frank Müller)

Not well visible, but the implication fits well to the fact that the light source mounting can be moved a bit around a pivot.


What careful viewing at photos can teach you, time and again.   


Maybe Frank Müller can provide additional information.

Though, the big question, how can we make ourselves an operational light slit projection system?

It might be hardly possible finding such an optical arrangement.



Eventually, to be continued in due course