A Selection of Relevant Magnetophon Patents
Page initiated 11 April 2013
Status: 21 April 2013
Friedrich Engel and some other fellows published an electronic PDF version of a book on the Magnetophon, the name AEG gave to the tape recorder. They invented technology and it is therefore logically that this must be regarded the official name.
This electronic e-book version (PDF) can be ordered at:http://www.beam-ebooks.de/ebook/40085
It is really a treasure having it. Albeit in German language, the many illustrations making it worth buying it, nevertheless!
In the industrial world every major invention is accompanied by at least a patent claim, as to keep competitors off for a while.
I would like to bring some of these patents to your attention.
Please notice: that in respect to patents there are two dates of significance. First the application date and second the date of its granting. In my perception, the moment an invention is claimed is the most significant moment. As from this moment onwards a claim is being covered, even when the claim is dated from long ago. Of course, most patent claims expire after 20 years, but even then those using covered inventions before the date of its granting are still infringing intellectual property, with all legal consequences! It might take sometimes decades, but even then ...
Uncertainty occurred after the hostilities in Europe ceased; German inventions were often regarded as a trophy of war. Some really were, although, most conflicts were later settled in a more or less gentle manner.
Please regard also our special Patent webpage
Please notice, that the patents marked (ap) means that these are curious patent files, which appear in the way the German patent applications were once handled. These patents, as a patent it is, owing to the DRP patent numbers, were sometimes claimed by the 'Third Reich Government', as to the benefit of their country. Since 15 January 1944 marked VO 15.1.1944. They (the applicants) were, nevertheless, getting a compensation for its confiscation! On the other hand, patents were handled by the Allies in post war days (1945 ~ 1949) being ' trophies of war' and many were shipped to the United States. Especially the interesting inventions were not sent back to the Germans before decades have passed. My guess, after the regular patents have been digitalised the German Patent Office started to scan-in these strange files, as to bridge the many gaps in their succession of patent numbers. I traced them in February 2006 coincidently (serendipity). In the British Patent Office they were very astonished with this finding! These files were not classified and do not appear in search systems. How have I traced them? The Allies ordered the Berlin Patent Office to make abridgements of all German patent applications between about 1928 and May 1945. Most carry, of course, an application number only, though, some does carry a granted patent number (~ 10%). Viewing, however, the microfilms the gaps only showed: This Patent Is Not Available. Even today, when you enter these numbers on the European Patent Website, the result will be negative! These orders resulted in so-called 'Blue volumes' which cover all German patent applications. These volumes are available at the British Patent Office (thanks to Tom Going who brought these books to my attentions in 1996), and I went through all patent series of interest several times. I also accessed German patents on different ways. Eventually, I brought home in the 13 years of engagement many thousands of patent copies.
CH227880 Claimed by Braunmühl and Weber of a stereo tape head. They invented the real HF bias technique; which was nonetheless claimed in the US before, though having a complete different nature. Both men also provided in a scientific way on what principle this technique relied upon.
DE500900 On behalf of Fritz Pfleumer, claiming what should become the well known basic recorder tape.
DE663413 Early tape recorder patent. Using a head with a tiny slit.
DE664759 The application of a capstan and also regulating the brakes of the two additional motors.
DE693664 On behalf of Weber.
DE700696 IG Fraben. Claiming an improvement on recording tape.
DE702298 Stereo head for tape recorders. Succeeded by (Zusatz zu) DE877370.
DE712759 AEG claiming a new way of theoretical play- and recording theory.
DE714053 Tape reel, which is having a time- or duration scale; this does make only sense when the tape speed is known. However, estimating tape length might also have been possible.
DE714123 von Braunmühl and Weber, claiming that a divided spectrum can be stored on two tape channels (like single channel stereo).
DE721198 4 slit rotary head, for expanding or reducing the audio pitch, to the Tonschreiber b!
DE732592 A very clever method fixing tapes on reels. Was especially used in combination with the wartime Tonschreiber apparatus (b + c + d + f?).
DE743186 von Braunmühl and Weber explaining the theory of the HF bias for sound recording heads. Their invention was challenged by an earlier US claim, though this guy did not gave the valid theoretical explanations.
DE743411 von Braunmühl and Weber, claiming HF bias and how it interacts.
DE745849 A very important patent, which shows a way how the tape centre-locking can be accomplished. This technique was used, for instance, by the Dutch Broadcast Service until the tape era came to a conclusion. Interesting is, that tapes are being stored without a reel in a special cardboard box. Certainly a very handsome method, maybe not for those being careless.
DE746940 AEG, a receipt for the material on recording tapes.
DE750777 A rather curious patent, claiming a tape which is having on both side magnetic layers. Please notice for what VO 15.1.44 is about.
DE751532 ap IG Farben. A push-pull technique for replay. By the way, this patent was not victim of VO 15.1.1944! (This patent is meant for sound films)
DE755431 ap (VO 15.1.1944) On behalf of Schallband-Syndikat (Tefi-Apparatenbau Dr. Daniel K.G.) Endless tape player, allowing free access to one of the tape tracks (multi track technique)
DE758309 Frequency dependable echo sound.
DE877370 Stereo head. Improvement (Zusatz zu) DE702298
DE882956 Synchronising non perforated film- and tapes by means an additional track utilising synchronisation signals as to keep mutual synchronism.
DE883836 Synchronising non perforated film- and tapes by means of the mains frequency (such as 50 Hz).
DE891465 Special off screening for tape-play-heads, as to prevent for hum induction. This techniques is also being used in our T8 Magnetophon.
DE971917 A method adapting the actual sound strength (pressure) onto the deepness of the record cutting.
DE972166 The basic patent for erasing tapes completely (removing at once its content by inductive means).
DE973824 Telefunken, HF recording head bias.
To be proceed in due course
By: Arthur O. Bauer
Please notice also: Patent-Auszüge!
Please continue, or proceed with the British post war report: BIOS 915
Please continue, or proceed with: Magnetophon Project