Nachtfee Survey page 3

Page created on 30 November 2011

Status: 21 December 2011


Please notice also: that this webpage is extended with new experiments after 25 December 2011 at Page 3a and on 8 January 2012 Nachtfee Inbetriebnahme (beginning to function). Nevertheless, this page is to be considered first.


Parallel to the investigations on the demounted modules showed in Survey job number 2 in our laboratory, I have started with determining aspects of completely unknown facets of the Nachtfee main chassis (frame).

It is, of course, debatable how one is starting this task but, since everything we have so far thought proved to be different; I strongly believe that it doesn't matter where we start with. The bits and pieces will, Deo volente, filling-in the many gaps encountered later. This apparatus is highly complex; and no information what so ever is mentioned on transformers wires and other means. (only the tubular tar capacitors and resistors indicating their values).

For instance, a servo motor - normally is connected onto a second servo-drive (slave, or Tochter) and is operating at, say, 300 - 500 Hz. There doesn't exist  such a counter device in this system, as there is no provision for it. For what purpose have they then used servos? My guess, that it is used as a kind of goniometer-phase-shifting device. How the system is working is still a mystery. However, it might be that the servo-search-coil is supplied with a 50 Hz signal. Eventually originating from a mains transformer, as one-out-of the two rotor coil wires is directly wired onto the scale-lamps, maybe used as common ground. Using 50 Hz is thus a serious option to be considered. When 50 Hz is employed, then the necessity of a power deflection stage is no longer a problem, only 90° phase shifting is necessary for one of the two deflection voltages or currents. Again, this is only a guess out of my many confusing considerations!

We have so many parameters to count with, that this undertaken seemingly is a bridge too far. As long as we cannot trace more technical information, of course.

Viewing the fact that this system had been built in the final weeks of 1944, and knowing that it was an irregular project (sonder Entwicklung), most components are, most likely, originating from civil part suppliers or stocks. By no means representing German component standards. I guess, that they lacked the chance getting good quality condensers. My experience from bringing one of the 10 channel modules in to working order, the two blocking Cs both failed completely (1x0.1 µF and 1x25 µF). What to expect from switching on the entire Nachtfee apparatus? One might face a smoke screen around it. Thus this way of approaching is out of the question.

Another option might be, trying to use an external power supply, and starting it up with very low HT, eventually supplying 220 V onto the mains transformers as getting the filaments running, as well as the servo supply (when it should operate at 50 Hz). As the HT is obtained by means of valve rectifiers, by leaving them out is ensuring that we have control over HT supply. Eventually with in series a small light bulb (lamp), which will absorb the too high system current. It is also possible, disconnecting the dubious tar capacitors at one end and bridging the gap by means of good quality types, and watching what a circuit is doing. Later the original situation can be restored very easily.

We have though, not yet decided what to do. Leaving everything untouched and never knowing how the system worked, or very carefully trying to discover what circuits are about. Viewing, however, the numerous blocks, most likely being transformers each having 6 pins, is also a challenge. Looking very carefully to some good visible places, after a while it proves often that sometimes is hidden virtually parallel, thus wired exactly underneath it, is (another) interconnection. There are numerous transformers of this kind which are hardly accessible. The only solution would be then - trying to get the circuit working and watching what signal eventually is being generated; and what is being fed onto or coming from it.

Viewing some of its components, there are some signs that the set ran for a while. Whether this had been during- or in post war days remains an open question. One consideration is, however, that some components show the typical signs of the interaction between humidity and high voltages. Often creating a replacement of the tar compound outwards. Aluminium cans are then bursting a bit open, and the tar-compound of roll-capacitors is pressing outwards. This phenomenon is mostly happening after a while. But when this set has become operational in the final months of 1944, there wouldn't have been much time available for humidity penetrating the sensible capacitors. Was this Nachtfee set under considerations for a while in the US, or had someone simply switched it on many years later? We don't know. But the clear signs still remain. I know from experience, that tar capacitors, when not being operated, never show signs of pressing its tar-compound outwards.



My first approach today is finding out what the purpose of this stage might have been. Please consider the previous considerations; and it is evident how dense the wiring around the left four modules is (three transformers and one blocking capacitor. And also the application of the dubious tar capacitors. In contrast the grey Siemens resistors are of quite good quality; and as far as being checked within their value limits


Viewing the wide space left free between the valve socket (G8B) and the top plating a power valve might have been operated. I guess that this might have been a power valve like an EL11 or an EL12. Valve number '14' most likely is a RV12P2000, the general purpose valve used in German equipment everywhere. After having checked pin 8 (the anode) and pin 1 being g 1, we may regard that this stage utilised an EL11 or EL12. My guess is being amplified by the consideration that a certain amount of deflection power has to be generated. Whether an EDD11 will do is for me an open question. Nevertheless, two EDD11s are in the Nachtfee system implemented.

Mr. Helwig Schmied brought up the idea that the CRT above the Order (Command) window might equal the CRT which is in the night fighter aircraft. This CRT is thus indicating whether the 'order' is having the same vector as is having the direction of 'order pointer' which is 1 : 1 linked with the order servo (Drehfeldgeber). In the night fighter aircraft a similar CRT display is (then) indicating what the (visual) 'order' (command) actually is. Necessary is, that both CRT trace-spots are strictly being kept in concert.


Considering the size of the output transformer I guess that the lower power type EL11 had been employed. Please notice that on the left hand side we deal with two transformers each having 6 connections

In the illustration I still have used EL11/EL12 only to signal that both types is to be considered, as they both have equal pin configurations. It might even still be possible, that my guesses are wrong, who knows? Time might bring eventually better understanding.

Quite confusing is the various resistances between several potential points. As to bear in mind that as little as possible should be changed, I would like to disconnect wires only in a few cases. Misleading sometimes is, that the ohmeter is always showing a kind of minimal resistance reading of a few ohms. Causing confusion whether one is looking at (tracing) a particular wire, or that one is measuring across a circuit. So far, transformers had often resistances of, say, 260 ohms; quite high value in my opinion. We have however, to notice that it is likely that quite low frequencies have to be amplified and handled. Asking for a reasonable amount of transformer inductivity.


Giving an impression how we are doing some of our investigation

On the same time, we also investigate the modules shown in the main Nachtfee chassis and in Nachtfee-Survey 2, though, now in our lab. which is located somewhere else; as we have there a far better equipped utilisation.

Again please notice, that determining where wires are running to is extremely difficult, as most wires are having the same colour, which are being bundled in GPO stile (PTT trunk like). Complicating is also, that all transformers I have noticed are having a similar connection layout with a 6 pin configuration, though, their inner wiring might differ. No sign what so ever is indicating a reference number nor a potential number, as is normally utilised in German commercial and military equipment.





On 7 December 2011

 I decided that it would make sense to connect the Nachtfee main chassis onto the 220 V ac mains.


The 220 V ac is connected and switched on. Please notice the safety lamp arrangement which allow us to connect the 60 watt lamp in series with one of the power wires


To be precautious we first inserted an additional safety lamp in series with the power cord. This cord was plugged in to a 'variac' which started up with a few volts ac only. We could do this safely as all valve rectifiers were not installed. The only thing we monitored was whether the 12.6 volt for the filaments is supplied. And it worked all instantly. At 220 V we measured 12.65 volt.



After cleaning some of the central illumination lamp-contacts all four worked as it had been done in early 1945. Please notice in the upper left corner the scale illumination pointing that a control is set at 160. Maybe not very clear but about 'South' the word: Pauke is coaxially written, the German word for attack of start fighting



After we had connected the HT at the chassis I measured that a power resistor was defect likely owing to a capacitor fault


I decided that it does make sense getting the entire electronics of the Nachtfee apparatus working. It proved that 99% of all tar-roll-capacitors are faulty, and that replacing them all is the only way getting circuits responding properly again.



As to access the right hand frame section, for replacing the faulty tar-capacitors, the Nachtfee apparatus has to be brought in the above shown position



Looking from the front we have first changed, call it bridged all questionable capacitors of the left and central frame sections. It is also necessary to handle the faulty tar-capacitors of the right hand chassis section. But this might be the most difficult part of the job, as one side of a capacitor might be accessible, but accessing the other side will cause serious problems


Luckily the number of faulty tar-capacitors is lower there. But bridging the faulty Cs is a demanding job, as each capacitor still has to be kept mounted at a single end. As to allow that all is to be brought back in its genuine state later.



Viewing the scale illumination is giving Dick Zijlmans a me a real thrill


The yellow HT cable clamed at one side of the smoothing choke and the blue cable connected on to chassis ground. It proved, however, that in former days, maybe caused in the US a series of blocking capacitors behind the vertical wires were all faulty and these had blown up in size [due to the interaction of moisture and the dielectric wax (hygroscopic phenomenon) versus HT]. Causing two broken ground (earth) wires. This fact is easing our work, as the eight HT electrolytic capacitors as well as the faulty block Cs are with their common grounds disconnected from the main chassis. Causing thus no critical situations yet. The valve socket on the right hand side is likely for the - 2  to - 4 kV? HT and I guess of the type RFG5. Although, I haven't found its anode connection yet.


I also could prove, that my estimation that an EL11 or EL12 might be concerned is correct. Bearing in mind the size of the small transformer cans I tend to believe that the lower power type EL11 is the one to be considered.


It was also possible, to determine what medium voltage HT (about 250 V) rectifier types is to be used. I tend to believe that it is an EZ11 or EZ12, the latter is the more powerful type. Please notice the two black G8 valve sockets above the smoothing choke. Which, by the way, might be of the so-called swinging-choke type. A system using a choke having a core that tends to become saturated. Well designed, it is acting as to stabilise the (HT) voltage.



On 14 December 2011

Dick Zijlmans and I both continued our survey with bridging capacitors, in the right-hand section of the Nachtfee main chassis.



Viewing from the front this section we look at the right-hand side of the big double beam CRT

It is evident that one side of the capacitor mounting is difficult to be accessed.


Viewing now from an opposite perspective. The difficulties encountered, is particularly getting access to a soldering point + getting at it your soldering-iron + one end of a capacitor-wire + fresh solder + enough light all at the same spot. Sometimes a very difficult job, as I don't like to burn my fingers, by the way!



The 'order compass' (Kommandogeber) being now removed


It was not easy to remove the entire system, as rust was also a hampering factor. Though, also knowing that 66 year old Perspex (Plexiglas) might be a bit delicate.



The 'order' or command scale being extracted

Interesting, which I never had realised before, is that pointing towards 'South' that vertically is printed 'Auto' what its meaning is I cannot judge. Just visible, coaxially printed, is 'Pauke'. Pauke often is meaning 'Attack' or start fighting (please notice our very recently discover British Most Secret A.D.I. (R.V. Jones) report 101 down at the Nachtfee intrtoduction page). It is also understandable why the lower scale region is showing signs of fungus like effects. This likely have been caused by the iron-ring at which the system is mounted inside the Nachtfee frame. The semi-transparent paper is (there) just a tiny bit too big and being touched (pressed) by the rusty metal ring and, I guess, due to the hygroscopic paper moisture creating a good fungus/rust environment. 



This photo has been taken as to notice the way the Servo pointer is being locked

However, interesting is that we just can read on the servo-motor: Fernsteuer-Geber (master servo), Gerät Nummer 127-205 K2A. It appeared that all three servo motors incorporated inside the Nachtfee system is of the same German GAF type.


Finally, the scale viewed with a different light condition


Also the centre locking screw (notice the previous 'order compass' photo) of the pointers is yet resisting our attempts getting it to rotate. We have sprayed some fine oil at it and have to wait until the next week before we will approach it again. We also ordered a special tool called in Dutch language: syfontang. A tool which is having plastic or rubber jaws; by which means the two Perspex (Plexiglas) pointers can be kept fixed in a position; and with some torque the screw being brought to rotate anti-clockwise (count 'o clockwise). A rather delicate job!



On 21 December 2011

we continued with a second attempt demounting the order scale, which is kept in between three Perspex (Plexiglas) circular disks


Dick Zijlmans and the author of this contribution, have decided last week that we necessitated a so-called "syphontang". As to hold grip on the small pointer centre.


It was also understood that a special tube fitting to the size of the servo motor, as well as to the space left between it and the screw-heads. As to ascertain that the arrangement is kept in a stable position during demounting work


Please notice also the rust traces between the large and smaller Perspex disks.


The order scale arrangement is actually mounted at the metal ring. The traces of rust are clearly showing what had happened in the past; the hygroscopic paper had absorbed the metal rust and the sad traces are clearly visible



Please notice the so-called "syphongtang" on the left. The centre locking screw and its attached pointer being removed. However, we could not rotate it against the servo shaft as well as pulling it off


Whatever we tried, no sign of any movement was noticed


We decided to use a three-legs-puller. As to hold grip we used thee metal rings which we put between the large- and small pointers. We also used "freezing spray" as to shrink the size of the shaft a tiny bit. It finally worked well and the small pointer was pulled off.


Both pointers shown together with a kind of rubber ring


Finally, the large pointer is also removed


Please notice the paper-scale which touched the mounting ring and the way rust and paper hygroscopic phenomenon has interacted


It took us some time before we discovered that a rather small screw was locking it against the large pointer shaft.


We finally were about to take the scale off. This was, however, not the real case, as we took this photo after we had cleaned the paper-scale from rusty particle dust originating from the rear side of the large pointer mounding. It also proved for us luckily, that we do not have not to deal with a form of fungus trace


The paper-scale being removed, we are viewing the middle Perspex (Plexiglas) disk. Actually there are two disks, which are being kept together by the rusty centre nut. Please notice also that the mechanism is fixed a bit off centre. As to keep this as was done originally, I decided not to change this situation and leaving it as it is


Paper-scale being photographed from exactly above. As to reproduce it photographically in an optimal manner


We have now several options, use the original scale as it is; or trying to clean it by means of a drawing or photo program. Hampering is, that the scale is illuminated from behind, thus the information, including text, should be kept a bit transparent. As is shown below.



We have not yet decided what the best option would be



To be continued at: Page 3a  (since 25 December 2011)



Please notice also our query page



Please don't forget to use the handsome: Nachtfee Chronology page


And, the PowerPoint progress page (converted into PDF)



By Arthur O. Bauer


Please go back to, or proceed with: Nachtfee starting page (status: 17 December 2011)

Please go back to, or proceed with: Nachtfee survey page 2 (status: 8 December 2011)

Please continue, or proceed with: Nachtfee survey page 3a  (Status: 25 December 2011)

Please go back to, or proceed with: Nachtfee MLK Lab. Survey (status: 13 December 2011)

Please return to, or proceed with: Nachtfee Inbetriebnahme (status: 4 March 2012)

Please return to, or proceed with: Nachtfee evaluation and conclusion page (status: 6 February 2012)

Please consider or go back to:   Nachtfee FuG25a project - investigating how the Nachtfee data was conveyed towards the aircraft display (status: 4 March 2012)

Please go back to, or proceed with: Handbooks papers and product information