Magnetophon K4


On Sunday 9 June we got donated most kindly the next shown apparatus.


Current status: 23 June 2024


Part 3  (Since 23 June 2024)




Photo taken in a kind of bird view


Type plate more in details

AEG Magnetophon

Type K4

Nr. 1906

220 V ≈   225 Watt

Year of its introduction 1938

AOB: Photo number 6 further down is giving a date of '8.41' thus it had been accepted (ultimately tested) for its application

(Photo-6   Photo-6return)

We may now draw the conclusion: that it is quite likely - that this apparatus had been manufactured about late 1941 or early 1942.


I consider its shape after 86 years very good


Viewing it from its right-hand side

The signs of fungus inside the lid is a quite frequent nuisance; occurring when there is no or hardly light around.

Normally this can be removed easily, more difficult is it - preventing that it is not coming back again.


We are particularly interested in:

Schematics, and documentation of all kinds,


The genuine Amplifier unit and, maybe, loudspeaker.


(3)    (Since 23 June 2024)

On 21 June 2024

we took a look what is underneath the AEG K 4 Magnetophon tape deck 

I guess that the tape-deck might weight at least 40 kG.


It proved to be quite difficult to demount the Magnetophon deck from its suitcase

Apparent certainly is, that its condition of say 82 years of age that it all seemingly was never seriously touched.


For this occasion I removed the black-box (up) cover plate, as to get an impression of what is inside

Please bear in mind - that this Magnetophon type still relied on DC bias as well as for erasing the foregoing tape content.


Our aim is, to show you as much various details possible

Tape-head assembly being removed.


The succession of the photos is following the sequence of what is being stored at my SD card


Photo taken just from a slightly different position, but nevertheless providing additional information


Please notice that this photo number 6 of today provides the day that this apparatus component had been accepted (= tested and therewith given free for application) on 8.41 thus August 1941!

(Photo-6      Photo-6return)

Google provided the translation of what is being named: 'start condensator' as: Starting Capacitor

I must say, its value of 16 µF is quite heavy.


Viewing it slightly differently


Quite some care for 'forced air cooling' has been taken, which might point at commercial applications

It is apparently provided by means of the capstan motor.


Down the cooling-fan housing we notice a typical mechanical relay often used as a system-break


I suppose that: the far right-hand side head is the tape erasing head

Left of it, I suppose, we notice the recording head and on the far left-hand side

we see the sound monitoring head.

As this configuration would allow final control of what has been recorded.

But, this is only my assumption.


Thus K1 = Wiedergabe Kopf or Play-Head

K2 = Aufnahmekopf  or Recording Head

K3 = Löschkopf or erasing Head

According my perception.


Head arrangement being separated


Head assembly being mounted

It is interesting to notice: that the Germans favoured, for evident reason operating the tape on the outer side; whereas the Americans favoured using the inner-side

My late friend Dick Lucas, was a professional sound recording man, he explained me why operating the active tape tape at the outer side: herewith was it possible to mark the tape-cuts.

This was then simply accomplished by viewing over the head assembly instead of each time having to lower your body as to accurately mark the tape-cut.

Also the way tapes very simply were reel-less mounted was known as 'AEG aansluiting' within the Dutch Radio Organisation; and, of course, all German organisations as well. Storing tapes necessasitated about 1 cm space on a shelve.

The next photo was taken about a decade ago (and is still on display):


Shown is our Telefunken T8 Magnetophon

Year of its production was 1948

and this apparatus once was operated at Radio Nürnberg, for their early FM broadcast test transmissions, since about 1949.

It is evident: that the layout concept is rather equal compared to their pre-war apparatus.

The tapes did not necessitate a tape-reel, as the tape back-side was made such that when winded up it was done steady with a certain torque;

please consider the sound winding-up of the tape.

The central lock was turned 90° and the centre bobbin including its tape could soundly being stored without any other means in their according card-box.



To be continued in due course


By Arthur O. Bauer