LMS10 versus CV64
The German, so-called Chinese, copy of the famous British CV64 cavity magnetron
Referring to the British postwar TRE report
T.R.E (TRE) report T. 1858
This report shows that Telefunken must have faced considerable difficulties during the production of the LMS10, which is a (Chinese)copy of the British CV64 cavity magnetron.
TRE proved, that their machining had considerable mechanical shortcomings. This might well have been owed to the wartime circumstances, as these tested samples had been produced in late 1944 or in early 1945.
The use of an additional getter facility, may indicate that Telefunken encountered sealing difficulties. Our own LMS10 (serial number 0587), like all other known samples, has a broken glass envelope due to its (brittle) glass quality.
Three of the tested samples showed, nevertheless, very good parameters and behaved like CV64.
During the Autumn DEHS meeting of 2005 in England, one of the attendees mentioned: that the Germans used linear strapping, maybe due to the lack of understanding of its principle. In my opinion this does not fit with the facts shown in this TRE report.
Bearing in mind, both photographs of LMS10 and CV64 and given the perfect parameters of three out of eight LMS10 samples tested, we have to conclude that his statement does not match with reality. What might have happened is, that the strapping of CV64 had been individually phase adjusted, whereas the Germans (Telefunken) employed not adjusted strapping(pre-fab.). The lack of efficiency of several LMS10 samples, may be owing to incorrect production-techniques (procedures) and wartime circumstances.
Considering the two photograph, the only instant observation to be made is, that it seems that the Telefunken LMS10 magnetron-strapping turned(rotated) in an inverse direction (maybe the opposite side is shown).
Brian Callick mentioned: that the Germans used in contrast a pure copper anode block, which is quite difficult to machine. Bearing in mind the shortage of qualified labour and the structural destruction of Germanys industry (late 1944), there had been, probably, no alternative to increase production quality.
Arthur O. Bauer
New recent discoveries
CV64 versus LMS10
After working on my CAVMAG 2010 conference paper called: The German wartime struggle to catch up with Allied Magnetron Technology; my attention was more focussed on the performance aspect of German power cavity magnetrons. Recently (April 2010), I kindly obtained from Rod Burman an opened version of the famous British CV64 magnetron.
Being firstly particularly interested in the question of "strapping".
During a DEHS autumn conference (DEHS AS05) some years ago, someone who had severed at TRE during and after the war told occasionally the audience: that it was found that the Germans did not understood the theoretical matter of strapping. As their magnetron strapping was straight forward only. Let us first look at the photo of the recently got magnetron device:
Let us compare now the reproduced TRE photo of an open LMS10, taken May 1945
When we compare both photos, we cannot directly see much difference!
When we consider the next CV64 image, which originates from the TRE report, we can clearly see that the straps are really bended and twisted
It is obvious, that in contrast the first two images does not show much of individual strapping
How is it then possible to judge that the Germans did not understand strapping? As strapping was discussed in Karl Fritz magnetron conference talk in March 1944 (please consider my comments down). Both samples, the first shown CV64 (serial number 4705) and the LMS10 which was opened by TRE in May 1945, have only very little signs of individual strapping (if any).
The CV64 serial number clearly is 4705
However, the CV64 strapping photo shown (third image) shows adjusted strapping though, this is not like what actually is visible on image one and two. The serial number of the reference CV64 was, according the TRE document, 1746. Whether this magnetron is the same one shown opened in the TRE document is not clear to me (third photo). We might, however, consider that during production numbers progressed strapping became more a matter of routine. Maybe even routinely mounted such that it prevented the system to jump (pulled) into another operation mode.
This matter got more significance after a new time-document was donated to our website. Containing the integral magnetron conference papers of March 1944, held in Breslau (since May 1945 Wroclaw). Dr. Karl Fritz gave a sometimes quoted, but never reproduced, paper:
Karl Fritz: Neue Erfahrungen mit Magnetfeldröhren bei Telefunken This contribution is from the historical perception very significant! As it deals with the fact that the Germans knew about Samuel's cavity magnetron patent of 1934. Though, also about "Alexejew's" cavity magnetron paper of 1940. In those days, the German-Russian relation was still very good. Fritz also stated that it is most likely that the British cavity magnetron inventors (Randall and Boot) must certainly have known the Russian cavity magnetron design! (p.102, at page 106 a photo of the Russian magnetron is shown). However, for us interesting is, that the Russians apparently used CW (continuous waves) and only applied a tungsten cathode! Consequently, never could have generated very high powers. I just recently found this reference in a DDR publication of 1957: N.F. Aleksejew & D.E. Maljarow: Erzeugung von Schwingungen großer Leistung im cm-Wellengebiet mit Magnetrons. Zeitschrift für technische Physik Band 10 Heft 15 1940, pages 1297-1300*
*Such a scientific periodical existed in Germany, I thus guess that it was a German language contribution.
Let us go back to the implications of the TRE report T1858
That most tested (captured) German magnetrons showed a high degree of failures, has to be seen in the context of the final days of the war. The LMS10 serial numbers are in the range of 853 - 862. This means that they most likely have been produced in the final weeks of the war (say, January - April 1945). Hence, at a time where enormous disruptions took place. As I have never encountered higher serial numbers as these; we might consider being one of the last batches produced. Who produced them, slave labours? A matter of sabotage must also be considered. It was not uncommon practice, that finally these where deliberately made to fail. Whether by German military personnel or otherwise. I believe, that this aspect must be taken into account before we can fully judge the outcome of Brian Callick's investigation.
About the CV64 construction
Karl Fritz also explained that the CV64 cathode mounting was not entirely sound.
We can clearly see that its cathode is off centre
This may be the cause why they have opened it, as it was a defect device anyway. Whether this was caused firstly by a broken glass filament input lead, I don't know) Touching the construction it shows that it at least must be liable to vertical vibrations (wobbling up and down). Not unlikely noticing the quite long cathode/filament mounting rods. I guess, that this mechanical downside has been overcome in successive (improved) magnetron types.
Diemen, 12 May 2010
Arthur O. Bauer
In the meantime (April/May 2010) I have read the very interesting book title: Mikrowellenröhren, Einführung in die UHF-Elektronik, by W.F. Kowalenko, DDR Verlag Technik Berlin 1957. I believe that this maybe is the best book of its kind. In contrast to what one might think, it refers mainly to US magnetron and related devices. I got this publication from Joachim Goerth, who obtained it from the Valvo Library in Hamburg after they had abondoned their valve production.
page 350 4.
Methoden zur Verbesserung der Trennung der Resonanzfrequenzen von Magnetrons
This paragraph deals with "strapping"
Bei einfachen symmetrischen Anodenkörpern von Magnetrons mit mehreren Resonatoren (thus having multi cavities, AOB) liegen die Resonanzfrequnzen so dicht beieinander, daß es nicht gelingt, die Anodenspannung bis zu Werten zu erhöhen, die zur Erzielung des gewünschten Stromes bzw. der gewünschten Leistung notwendig sind, ohne daß die π-Mode in eine andere Mode umspringt (π represents in mathematics a 180° phase difference; the number of cavities in magnetrons is always even. This means, that each boarding or adjacent cavity is having an opposite electromagnetic field. Excitation spikes which rotate around the cathode is always feeding equally polarised cavity slots. What he points, is that mode jumping can be prevented by carefully selecting the anode voltage, which practically is impossible when operating in 'pulse-mode', AOB). Um also die Leistung und den Wirkungsgrad erhöhen zu können, ohne die Frequenzstabilität zu gefährden, müssen besondere Methoden zur Erhöhung der Frequenztrennung bei Mehrschlitzmagnetrons gefunden werden. Zur Zeit gibt es zwei Wege der Verbesserung der Frequenztrennung: die Anwendung von Koppelringen und die Verwendung von Anodenkörpern mit unterschiedlichen Resonatoren. (so-called 'rising sun systems, for which each time both opposite cavities are of unequal size. Their actual operating frequency is the sum of both individual cavity wavelength properties. For say high end magnetrons at ≥ 3 cm, the straps like shown in the above photos are too difficult to handle in those spectra, AOB)
Die Koppelringe (straps, AOB) bestehen aus ringförmigen gebogenen Bändern oder Drähten, die jeweils jedes zweite Anodensegment untereinander leitend verbinden, d.h. der eine Ring ist mit allen geradzaligen und der andere mit allen ungradzahligen Segmenten leitend verbunden. Die üblichen Ausführungen sind einfache zweiseitige Kopplung, wobei der eine Ring an der einen Stirnseite des Anodenblocks und der andere Ring an der Stirnseite montiert ist, sowie doppelte zweiseitige Kopplung, bei der an jeder Stirnseite je zwei gegenpolige Ringe angebracht sind. (thus, on each side of the anode block, AOB) Bei der π-Mode addieren sich die Ringkapazitäten (strap capacitances, AOB) zur Schwingkreiskapazität. Dadurch wird die Wellenlänge der π-Schwingungen bei Vorhandensein von Koppelringen erhöht. (The existence of straps is thus increasing the overall cavity wavelength resonance, thus lowering its frequency, owing to the introduced strap loading, AOB) (The π-Mode is owing to the strapped lines moving or converted to the lowest frequency spectrum possible, AOB)
Die Anwendung der Koppelringe in Röhren für Wellenlängen von 3 cm und weniger verursacht erhebliche Schwierigkeiten bei der Montage, und die kleinen Abstände zwischen den Ringen führen zu großen HF-Verlusten und Verschlechterung des Wirkungsgrades. In diesen Wellenbereich wird darum von der anderen Möglichkeit zur Frequenztrennung Gebrauch gemacht, der Anwendung von unterschiedlichen Resonatoren im Anodenkörper. (The quintessence is, that it does not make sense to use straps for very short wavelengths such as for say ≥ 3 cm, strapping is too complicated and is causing too much energy loss. Here the rising sun magnetron technology is favourable, AOB)
In the meantime (2005), Rod Burman sent me some photos of a test rig, of which the thinks that it was used for: cold-strapping-tuning
Regard also, or go back to: Boot and Randall's famous cavity magnetron patent of 1941
Consider also, or go back to: J. Sayers strapping patent US2546870
Regard also, or go back to: H.J. Fischer's contritubion on strapping theory
Consider also the famous MIT paper on: Strapping technology
Back to: Berlin FuG 224