DMG 5k




Page initiated: on 29 February 2024

Current status: 14 April 2024

Part 2   (since 8 March 2024)

Part 3   (since 16 March 2024)

Part 4   (since 23 March 2024)

Part 5   (since 30 March 2024)

Part 6   (since 6 April 2024)

Part 7   (since 14 April 2024)


This photo originates from the end of January 2023, when we just received it on a long-term loan



We have moved with the assistance of Hans Goulooze the DMG5k to a place (facility) where it should be possible to undertake an elaborate restoration



The new DMG5k restoration facility is just adjacent our current Nachtfee repair endeavour


 I would still like to let run our opened Nachtfee Console in the repair mode; as to become really sure that the annoyingly repeating deflection faults being since really cured.


The most low plug-in cabinet is the mains controlling module containing on its far right-hand side the two 'Automatic' fuses (Selbst-Schalter)

The grey circle is actually the main-on/off switch, of which the knob is failing.



On this trolley-table we should be able to repair or accomplish our necessary measurements

What, however, we need then first is at least a pair of extension-cables, which Dick Zijlmans promised me to bring along next Sunday (3 March)



Luckily we found a knob which, with some adaptation does fit to the wanted purpose

The on-off switch is in the schematic belong designated with '3' (inside the circle).



Schematic of the module dealt with below

The 220 V mains is to be fed onto the connections 4 and 5



It is evident, that this module has been build quite condensed



Considering it from a slightly different perspective



Please compare the 'pot-core' numbers with the schematic (6a.) above Though:

The painted pot-core numbers do not match with the schematic (6a) of above, but doubtless it concerns just these 6 coils (forming a chain of low-pass filters).



Viewing the 'pot-cores' just from their sides



The finger of the thermo-relay are just visible in the vertical centre



It proved to be quite difficult to access the neon indicator lamp-holder, which 'bayonet-neon indicator bulb ', you might recognise down in the centre

Which is fit with two base-contacts

The lamp is still glowing yellow/red, but it is inside showing a black coloured deposit on inside of the glass-bulb.



(2)   (since 8 March 2024)

Below on the right-hand side we notice that the revised power-switching module had been inserted in the DMG5k frame again

It proved that the manuals we possess does not imply a sound cabling plan as well as is lacking the detailed schematic of the power-supply module.

It becomes necessary to find out these aspects ourselves. The Hans Goulooze and myself have started a new survey.

What and where do we trace the mains connections.

Firstly, we start with checking by means of a simple ohm-meter what the according pin-connections.



Dick Zijlmans necessitate more time than he expected, we still are lacking the according extension-cables. Instead, we are using first an extension cable used in conjunction with the FuG 10 system. Inadequate, but we need only to extend two cable pins.



The extension cable substitute is linking the 220 V connection onto the soundly constructed DMG 5k Michael power-supply


Now we should focus first on the core of the entire system: the power-supply.


After having removed the various module covers, we get some idea of the various shapes of the separate sections




After connecting mains onto this module and no response could be notices; my attention was drawn onto suspected electrolytic capacitors.


We have now noticed the rear of the power-supply from three sides


Soundly build it certainly is!


We found three electrolytic capacitors, but these were mounted at a non-accessible place


We first tried to access them by removing the bottom-plate, though in vain.

Apparently there must exist a different way.

In such cases: do always consider that it concerns: a German type of equipment, and smart mechanical engineering is almost likely involved!

And, indeed, it is!

All proved to be mounted modularly!



AOB: my first approach, is always try to removed first what is easily to accomplish!

The German engineers of the Luftwaffe employ easily to understand systems.

The fixing screws are always being marked by engraved red circles on top.

Only two screws had to be turned anti-clockwise a few turns. These will remain in the module - due to their thread free section.

Please look closely at the upside turned module, and notice on the far right-hand side that the fixing screw is still hold in the base-plate!

Connectors being lavishly employed without causing mall-functioning. 



The forgoing module now viewing it more in detail on its side

You can also now see the two module fixing screws due to their still dead-threat(??) Re-mounting the module becomes very easy!

The tubular capacitors are of the expensive "hermetically ceramic sealed-off" type; these, even after 80 years, will function like these were newly accepted in, say, 1943!



The second module removed is also a sound master-piece!

The two black devices around its centre might constitute  a voltage- or current regulator. The circular device on the right-hand side nay be a current sensitive coil-system; the black square device may constitute a variable current device.

Though, because we still do not yet have access to an integral circuit drawing, quite much is using the experience of my 'grey cells'. 



The number '0' always indicate ground-level



After some experiments, Hans drew the conclusion that these hexagon-extensions had to be removed as well



Voil also this barrier had been accomplished


It is so logically and soundly constructed!


The certainly defect electrolytic capacitors are visible through the lower holes in the bottom-plate



AQs to get really fully access to the three electrolytic capacitors, it is necessary to remove also the heavy transformer

Which is quite easily maintained as the cable-tree-wires being fixed 



The three electrolytic capacitors have to be replaced

We tend to access the aluminium cylinders and insert modern types

  The problem might be, that the specification tells us 550 V average 450 V; whereas most modern types of the 450 V types.



Please bear in mind, we have to cope with the circumstance, that we do not possess a detailed electrical schematic of our power-supply

However, what we, Deo volente, may bring-in is more than half-a-century experience, of tracing faults.





(3) (since 16 March 2024)

Ultimately Dick Zijlmans, very kindly, managed to supply us with a bunch of extension-cables he made

Now we can approach our DMG5k survey more seriously.



  Visible is the way these type of cables are matching together; it is even possible to put 2 extension-cable in series as to widen the space between the unit under test and the system-frame



Looking at a new schematic someone so kindly did copy



The component numbers differ from those noticed on the schematic, though, the wire numbers still do match, and we can trace where various components being drawn on the schematics




We notice above the three electrolytic capacitors, which was to be replaced

As to keep matters as it had been before, we have to remove the content of the inside the Al cylinder.

After all not a too great problem.



Dismantling was unexpected simple

Afterwards we cleaned the inside with hot water, as the electrolytic residues have to be removed.  



Viewing the application of an extension-cable differently



When someone has to access plug-in units under operational conditions, extension-cables are essential



Considering it from a different perspective



Slightly complicating is: that nowadays most HT electrolytic capacitors being made for 450 V max.; whereas our DMG5k, particularly in the start-up stage is passing 500 V by far (max. voltage rate printed at the Al cylinder 550 V

We therefore have decided to implement two electrolytic capacitors in series. As to counter production difference, we will implement low power resistors as to secure that the two electrolytic capacitors being fed with about equal dc voltages.

The bigger two capacitors possessed 16 F and we employ two 45 F capacitors in series, making 22 F and a max. voltage of 900 V.


(4)   (since 23 March 2024)


Hans' aim today is to build-in the former electrolytic capacitor housing

We only possess printed-board electrolytic capacitors of 45 F and max. 450 V

However, the genuine electrolytic capacitor was 16 F, but designed for a max. voltage of 550 V; and preliminary experiments showed us that the unloaded voltage rises up 500 V.

Therefore we have to use a staged arrangement with two 47 F devices in series.

As to keep the voltage division within limits we decided to arrange two resistors of 2.2 MΩ in series, as to force the system to be loaded more or less equally.



Hans is relying upon silicon based insulation sheet (red-colour)

please notice that two capacitors being stagged.



After Hans sealed the Al tube (more or less) we accomplished load measurement

We were astonished with the actual behaviour of the two electrolytic capacitors in series.

Very erratic current was flowing; albeit with reduced currents.

But irregular it remains.

As to look whether this special capacitor type was causing the nuisance, we compared a heavier type though encountered more or less similar phenomena.

The only thing we might have noticed was that after changing to another electrolytic capacitor and returning later to the foregoing sample - it might be that we encountered a bit less erratic current-flowing; but we aren't yet sure that all will later operate correctly.

This unexpected nuisance might have been caused by the so-called 'formateren' (Dutch language) effect. As electrolytic capacitors being based upon an oxide-skin-layer deposited at an aluminium electrode (negative contact) and a positive counter-electrode.

We measured sometimes in the range of 10 - 30 A at a 365 V dc loading.

We dedicated quite some time in trying to understand the many phenomena we encountered; we certainly have to continue these measurements as to get an 'feeling' of what actually occurs.

Might this being caused by the fact, that the modern type electrolytic capacitors differ in their behaviour compared with the old type densely filled with electrolytic liquid?




With some brief skills - the second electrolytic capacitor was more soundly closed than was the first one



(5)   (since 30 March 2024)


On 28 March 2024

We continued our DMG5K endeavour


Testing now the last electrolytic-capacitor replacement

Our aim now was to view what its current leakage at 365 V dc is.

After a while we measured ca 90 A ; but please remember that we additionally integrated 2 x 2.2 MΩ is series, as to keep the centre of the two 22 F electrolytic capacitors being kept at about half of the supplied dc voltage across the two connection wires (black and red). (Roughly 87 A already is flowing through the 2 resistors in series, which equals about what is shows on the current scale of our test setup.   

Its minus (pole) isn't grounded directly and is wired by means of wire number 31 connected onto an outgoing pin connection (please notice the following schematic accordingly).



Viewing a bit more accurately



Hans placed the "Netzteil" (power-supply) at its fixed position, on its carrying frame again



The mounting frame for the additional 3 electrolytic smoothing capacitor demanded careful considerations as to be certain that all being rewired correctly



Please notice the three electrolytic capacitors numbered 68 and 70 being nominally 16 F (in our new case each one  ca. 23 F) and the one left of the foregoing 66 being nominally 8 F (since replaced internally ca. 11 F)

We discovered:  that a modification accomplished according production stamps between July 1950 and 1952; the 8 F capacitor once had been connected incorrectly.

Before demounting them we cut-off the wires but left just some as to notice their according colours.

Wire number 94 doubtless is of red colour and wire number 31 accordingly black coloured; whereas the red capacitor wire was soldered on it! After we did remove the cable cover-insulation we encountered a 'black' cable-marking!



5 = bertrager (transformer) number 5; constituting the loaded 300 V dc; as well as 12.6 V for some of the filament circuits


Considering the wire-connections a bit more in details; though not yet fully insulated

The yellow-coloured wires are fire- or heat resistant of which the yellow shining originating from heavy wounded silk; wound in two counter-rotating spinning. Very nice flexible cables, provided in various strengths. Also the red coloured wires being of comparable favourite qualities. 



The wires being now insulated effectively (using heat-shrink tubing); also the transformer 5 being re-installed again



Everything being refit appropriately and we suppose next to connect 220 V ac on the system

Of course, nowadays we  count with 230 .. 240 V ac mains, but we consider we should operate the system by means of a 'variac' provision adjusted at 220 V ac.

Such a provision allows us to start measurements with rather low voltages.

For security, I prefer to start up by means of a series light-bulb which - when all performs smoothly, can be safely short-circuited.




(6)    (since 6 April 2024)


 On 4 April 2024 we continued our DMG5K survey


Having started, it  became soon evident that - due to the complexity of this technical subject, and the encountered nuisances, that it does make sense to start with my photo series first, and thereafter, I will go into the various technical implications and uncertainties.

Mostly being caused by the very fact, that the main frame wiring schematic is, in some respect, using two different numbering systems. Which I have, designated the old-  and the new numbering.

Why I don't know - but I suppose that for whatever reasons, the DMG5K frames once had been modified. And, consequently, the genuine techniques which remained, maintaining using their old wiring number designations. Whereas the successor system employed a new wiring system, and their according modified wiring numbers.


Our aim today had been: to investigate the behaviour of the 300 V stabilized power supply



As to setup a test of the plug-in number V, constituting the main power supply (some being integrated separately in plug-in module (Roman) VI) - down in the main-frame with the yellow glowing indicator lamp and typical German automatic fuses)



Considering the schematic of this power-supply it was evident that some crucial electronics were not yet understood; which will be dealt with separately, later




We we experimentally interconnected some connections (the wire numbers '30' - '31' and '0'). This erroneous estimation caused quite some implications, which had later to be solved. It proved to be necessary to go quite deep into the nomenclature of a different plug-in units including (Roman) VI

One of the implications can be seen on the next schematic: 



Please notice yourself why we in first instance had to interconnect the lines (wires) designated '30' - '31' and '0'

As we otherwise would not have had any HT at all, as the minus contact of the rectifier-bridge would be open and there could not be supplied HT voltage!

That this proved to be an in-valid estimation, we will later learn more about.

We discovered, however, also that we encountered number series, which did not match together.


But, the kind of surveys (Entdeckungsreisen) we generally accomplish, are also causing a forced learning process; which is really necessary to grasp the essentials of circuitries. As 'misinterpretations'  are necessary to learn about their implications.

Your will virtually remember such matters for the rest of your life.  


The 'variac' transformer has been set at about 130 V only, but the 300 V stabilisers were already becoming overloaded!

And, the filament supply which should be 12.6 V ac did  not reach about 7 V ac!

Thus, there must be something fundamentally wrong in the high-tension (HT) circuitry!

But, let us first follow the line of photographs I took that day.




When you look closely down the 'STV' (Stabilovolt an enterprise owned by Lorenz a substitute of the American ITT) symbol

This was indicating that the HT had reached already ca. 300 V at a system supply of ca. 130 V ac!

It is evident, that the stabilising current flowing through the stabilizers are reaching their limits!



Because, as I already noticed, that we encountered schematics with not matching cable (wire) numbers, we decided to measure each of the wires ('30' - '31' and '0') from point to point separately.

Hans down approaching the mains power section whereas I did read-off the Fluke meter.



Luckily, we possess Dick Zijlmans made extension cables, so I could easily handle the matter by simple means




We really did our best to understand the circuitry, but in first instance, we missed some essentials!


We leave the state of affairs, and remounted the two, removed modules


This is a quite easy job as all fits exactly together and being fixed by two or three market screws together



Screening off the power supply firstly

But, we removed it again after we considered that we should finding out, what the problems actually were causing.



One consideration was: might it be that the problems of too much overloading of the stabilizers was being caused by the lack of current consumption in the system circuitry?

It proved, however, that this wasn't the case.




Viewing it from a different perspective, we notice now that the units on the table being interconnected with the main-frame of the system.




Viewing it differently



After I inserted the RV12P2000 valves in the receiver plug-in module (Roman) II, I started measuring the various anode and screen-grid voltages

These responded as I expected, and therefore left it for the time being.


Thereafter I pulled-out one of the STV stabilisers so that these could not be overloaded and adjusted the filament voltage at about, say, 12.6 V ac.

The HT now rose beyond > 500 V dc!

Then we disconnected the lines marked '30'- '31'and '0'

Now, we had no longer any HT available. We disconnected the line '30' from the connectors

and instead,

we used our universal laboratory HT power-supply.

This was already the state of affairs when I measured the values of the anode and screen-grid voltages of the receiver module (Roman) II.


I would like now to approach the nuisance we encounter with the far too high HT output.

Let us match the three essential schematics together; of which one is the:

First is the power-supply schematic - the second one is the schematic of the mainframe wiring, and the third one is the small mains switching circuitry.

Not yet explaining but to get some feeling of what the problems are about.




Abb 31 (from the wartime ↓ manual) Schaltbild des Netzeingangsteiles


We have already noticed the line (wire) '30'; please jump to first schematic (85a.) and look at the upper bridge-rectifier designated '63' and notice its minus contact line (wire) '30'; please follow the line until it leaves the power module.    Thereafter consider the next schematic within the red circle marked 'b'.  And notice a bit down at the line contact number '12'. Please look now a bit carefully and notice the designation: 'V 30' (it looks a bit like a 'Y' but it should be 'V' as the is pointing at plug-in unit (Roman) V which's schematic we have already noticed firstly.  Though, frame cable (wire) number '30' is now becoming line (wire) number '12'.    I suppose that this might once have been caused due to some modified systems, where the mains input module remained in service whereas the rest had been redesigned. The clue or name it solution is provided by a kind of conversion table in the bigger module (Roman) VI. Thus, on the left you notice the numbers maintained in the old type module, and on the right we notice the main-frame lines (wires) including their (Roman) plug-in numbers (I ... VI).

Please, let us now consider the third module, mounted in the lowest right-hand corner of the main system frame.

It is designated Netzeingansteiles (87a)

Briefly translated: Mains (switching) interface

Let us consider '12' which actually is equal to the line (wire) '30' originating from the negative connection of the HT-rectifier-bridge designated '63'.    But we know (from the wartime manual) that within the mains-interface component numbered '16' constitutes a thermo relay. Such a device normally responds upon heating-up due to current flowing through a coil which heats-up a bi-metallic switch.    But there cannot flow a current as long as the thermo-relay coil isn't loaded with a certain (sufficient) amount of current.     Let us now first consider wire (line) numbered '2'. when you follow the circuitry we notice that the latter line is also flowing, via the thermo-relay coils towards '0' and '0' commonly is the symbol for ground.    Though, let us neglect the other components first; that when the thermo-relay switch being activated the line '30' via wire '12' can flow towards wire (line) '11'. Please return now again towards the red circle 'b" and let us view where line (wire) '11' being wired onto.


Contact '11' (left-hand side) is connected onto VI 80; here we encounter or an printing or drawing error: VI is indicating that we remain in the frame bottom section and is being connected onto power resistor (50 W) designated '14'. I interpret that is printed 10 but it should be number '80'! However, the current flows through the resistor reaching point '81' which is a logical consequence of the foregoing number '80'.    However this also being fed onto another 50 W power-resistor (designated '15') is in the schematic on its right-hand side connected onto '0' thus ground. Now line (wire) '30' being finally connected onto ground. Consequently, when current is flowing that there will be a voltage drop across the two power resistors designated '14' and '15'. Whether this will be sufficient we cannot yet determine.


Please, notice the two high-power resistors (green porcelain) at the rear side of main-frame (on the left-hand side in front); both constituting the resistors '14' and '15' in the schematic (86a) Leitungsplan des Gesamtgertes (within the red circle marked 'a')


The mains-interface module is mounted inside the black box down on the left-hand side.


Let us now take a closer look of what it is about:


The two thermo-relay (vertically mounted) switching contacts-fingers are visible left of the two ceramic automatic fuse/switches

The wire-wound resistor is in the schematic of Netzeingangsteil (87a) designated '17' and, in my perception determining the switching parameter of the thermo-relay.



Finally what is actually causing the thermo-relay to switch on?


Please return again to the second schematic and consider the red circle marked 'b'.

Please, consider in the box Netzeingangsteil VI contact 2 and read off on the outside we notice: (Roman) IV '21' and V '21'.    V '21' is pointing at plug-in unit (frame) of the power-supply (plug-in unit Roman V).    Please consider here fore the first schematic (85a). And line '21' is supplying - 12 V dc, originating from bridge rectifier '76'.    Hence, the thermo-relay is simply being supplied from the main plug-in unit (Roman) V. When the mains switch is being switched to 'On' the - 12 V is heating up the thermo-relay coil. And after some time - it will click in the on position. I suppose, at least delaying the heating-up period of the valves.     When the thermo-relay is being activated the circuitry is keeping it 'on' status.


Whatever someone may think about our today's survey, I hope that you, at least, enjoyed it.   


(7)   (since 14 April 2024)

On Friday 12 April 2024

Our aim today being - to test firstly the 'thermo-relay' in the mains-entrance module.

I would like to repeat the circuitry of the mains entrance module.


Our objective to day was first to look whether the 'thermo-relay' was correctly operating

My screwdriver is pointing at the main 'thermo-relay' contact fingers.


The main fingers is connected onto ground and being wound-around by some resistor-wire

We have measured roughly that the delay time differs between 8 to 10 seconds.


When the bi-metal finger reaches its critical temperature is bents and is causing the contact wires '2' and '46' to inter-connect.

this is causing that relay '18' to switch on and herewith it is causing a current-flow between the wires '12' and '11'; thereafter the circuit keeps itself being operational.


My screwdriver it pointing at the relay and its switching contacts

The next YouTube film is providing a better understanding of what it is about.


Film 000164:    Please notice first the relay and its according contacts in front. The finger-pair, being activated by the relay designated '18'. Please notice the left-hand side taller switching-fingers. The most left-hand side one is wire-wound by some resistance wire; which is heating up the bi-metallic left-hand side finger. In front you see the two sets of switching relay contacts. The bi-metallic fingers are moving, when a certain temperature has reached, to the right-hand side. The adjustable resistor in front is to adjust the switching-on time-delay.    R 1 designated black tube is the housing of the 220 V mains supply neon-indicator. Please view carefully the slowly responding bi-metallic finger towards the right-hand side. The sound of a buzzer is indicating the instant the circuitry being activated.  

I would like to advice you, to view this film more than a single time. Because you notice a progressing process without really noticing that something is moving.


The mains entrance unit has been re-mounted

After we noticed that it operates soundly.


It would first like to recall a foregoing wiring plan


The voltage across the two high-power series resistors '14' and '15' as being shown with circle a

On the left-hand side of resistor designated '14' we notice line (wire) '80' (however you might read '10' but when you view on the right-hand side of resistor '14' the we notice '81'


The two resistors in series are constituting the actual resistor in series with the minus connection of the bridge rectifier designate '63' and particularly wire (line) '30'; on the next following schematic


We encountered a far too high HT level of (measured with one STV 150 pulled out) of ca. 500 V dc


The curious remedy was implementing a series resistor arrangements of component '14' and '15' towards ground.

Let us now notice what is measured at the terminal (wire) 20 of the HT -  as well as at line (wire) '30' connected onto resistor '14' point '80' (inside the red circle designated 'a')




This meter is measuring ca. 230 V dc across point '80' and ground '0' (86a red circle 86a circle 'a')



We are measuring ca. 205 volt across the HT line '20' in the foregoing schematic (85a) against ground '0'

This is ca. 100 V too low, as it should be about 300 V.

Though, as to simulate a kind of operational condition I have loaded the HT line ('20') with a 30 W light bulb. (actually two 60 W bulbs in series as we do not possess a better HT load).


This bulb is only operating at ca 205 : 2 is say ca. 100 V


After we trusted that all is functioning correctly we attached the two demounted modules again

The two silver-shinning glass envelopes are constituting the two two STV 150 V stabiliser devices.

Please compare schematic designated '72'and '73' loading line (wire) '20' (schematic 85a)


Again noticing the mains entrance unit, with a glowing neon indicating the mains being switched on


Again the system is operating quite smoothly now


It is quite astonishing that the system operates after say, 80 years so soundly!

Let use closure today the survey with a second YouTube film


Film 000171:    Again we start with no mains (220 V) being supplied (using a variac transformer) which is adjusted at about 220 V ac supply. (Please be aware that I notice "within the red circle 'b' whereas it should be, within circle 'a', instead!  The 'thermo-relay' delays about 8 10 seconds.   The two meters being not operated at similar sensitivities. The left one being operated via the 1:10 voltage divider (x10)!



To be continued in due course


By Arthur O. Bauer