FS: WW II Magnetron GL-5J29 marked Classified, NOS

As I recall the eBay listing, it was stated that the magnet was not included. Of course that means the cavities are also missing. You are correct that what is left isn't a magnetron.

Don

What's the point of having cavities in your magnetron if the glass gets in the way of the electerons?

DNA

I've got 2 tubes that look just like this sitting in a cabinet in my office. They were there when I moved in, so I'll have to ask someone what they are. I'll have more info tomorrow.

-

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

-----------------------------------------------

--
http://www.r-type.org/exhib/aac0088.htm

And the qaulityof the copper is imporant too.

Graham

This is better.

Certainly not a *resonant cavity magnetron*.

Graham

Hi,

It is a split anode magnetron with the filament (and its tensioner) visible just under half way along from were the pipes enter. From there it passes through a disc that is designed to stop electrons being sprayed out onto the glass envelope and then into the space between the two anodes. The thick pipe is both for tuning and water cooling - one of the filament connections being visible next to the water inlet. The reason there is usually no magnet with these tubes is that it is left behind in the equipment.

This type of tube was known before WW-II being developed by both the Germans and the Japanese. There are no cavities in it, the anode being made of two blocks with semicircular cutouts allowing room for the electrons to swirl around under the influence of the magnetic and electric fields; operation being rather similar to the well known cyclotron. Randall and Boot's cavity magnetron didn't really come onto the scene until about 1940.

Cheers - Joe

Thanks Joe - nice tutorial!

Andrew VK3BFA.

Well of course it is. The cavity (or cavities) are part of the magnet assembly.

Don

"Joe McElvenney" wrote

===========================

R & B's cavity magnetron was developed at Birmingham University in the midst of the air raids on that industrial city. We can imagine R & B having to hide under the workbench whenever a descending bomb was heard, culminating in a loud bang and broken glass.

The ingenious device generated a peak pulse power of 50 kilowatts at

3000 MHz. Pulse repetition frequency 400 Hz. Pulse width 1 microsecond. So far as I can remember there were 6 or 8 cavities milled into the copper block. Alternate anodes surrounding the cathode, and close to it, were strapped together at their ends via copper bars. The block diameter was about 2" and about 1" thick. The magnet was a U-shape with pole-pieces which closely fitted the flat ends round the block such that the magnetic field was parallel to the cathode.

Because the luftwaffer in 1940/1 had more bombers than the RAF, and in view of its potential as a war weapon, Churchill personally banned installation in RAF aircraft in case the top-secret device should be shot down over Germany and fall into the hands of German scientists and engineers.

So Churchill handed the cavity magnetron to Roosevelt as a free gift in return for 50 rusty, old, WW1 destroyers. The manufacturing capacity of the US radio industry far exceeded that of the UK. Not to be outdone, the Americans soon produced a 10,000 MHz version.

I first held one in my hands in 1945 by which time centimetric radar had been installed in RAF Catalina and Sunderland flying boats on convoy-escort duties in the Battle of the Atlantic. By 1945 German submarine crews were on suicide missions like kamikazi pilots, only 1 U-boat in 10 returned to base.

There are more than 100,000 merchant ship and U-boat crew-members sharing Davy Jones locker at the silent bottom of the North Atlantic Ocean.

Once having detected a centimetric radar beam, and being accurately located themselves, submarine commanders preferred to remain on the surface, uncover the guns, and fight it out, day or night.

During most of the war there had been little effect on German industrial production by RAF raids. Many bombs fell on open fields and sometimes killed cattle. But by 1944 RAF navigatigators had maps of rivers and cities laid before them. More than a 1000 heavy bombers, Lancasters, could be put into the air, night after night.

With radar they couldn't miss whole cities and individual districts. Nevertheless on one occasion more than 100 bombers, complete with crews, failed to return to base. Such occurrences greatly exceeded the capacity of factories to produce them and to train aircrews.

During the last 12 months of the war, radar equipped RAF bombers killed more German civilians than died in the concentration camps. Hiroshima and Nagasaki, which came shortly after, were just chicken feed. Air Marshal "Bomber" Harris was never knighted for services rendered.

The main beneficiaries of R & B's invention of the cavity magnetron, done amid the high-explosives and incendiaries falling on Birmingam, have been the Japanese and other Far Eastern peoples who have manufactured many millions of cheap, reliable, microwave ovens.

And of course the many millions of people like you and I who benefit from daily hot meals. I detest barbiques.

There was held in the Kensington, London, Science Museum, the original prototype of the cavity magnetron without its magnet. It was in a securely locked mahogany and glass case and looked, as I recollect, like a small dirty can of baked beans with things sticking out of it. It may still be there.

Makes a change from so-called SWR meters.

--
Reg, G4FGQ.

Your research is incomplete.

Don

I read in sci.electronics.design that Reg Edwards wrote (in ) about 'FS: WW II Magnetron GL-5J29 marked Classified, NOS', on Fri, 23 Sep 2005:

They were a very great deal better than not having them.

I think that's a bit off-beam. The 3 cm device was a joint UK-US effort. But, to a very large extent, once the principles, in particular the cross-strapped anodes for mode suppression, were established at 10 cm, the 3 cm device was a matter of dividing the dimensions by 3.33.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Wrong Don !

Graham

There's something I've wanted to ask since the microwave portion of USAF tech school. It didn't come up, because my specialty was ECM (Electronic CounterMeasures), and all of the transmitters in that field are intentionally as noisy as possible, since their purpose in life is to jam.

But for, for example, radar, does a magnetron normally put out a relatively "clean" sine wave? One of our jamming transmitters was series-modulated with a 4-400A. (I once checked a brand-new, in-the-box 4-400A out of Bench Stock and gave it to a buddy who built a 20M linear with it. Being a tech in the USAF was kewl. ;-) )

Anyway, I know they're typically pulsed for radar, and a microwave oven doesn't care about the waveform; in fact, probably the raggedier/noisier the better for something like that, but during a radar pulse, is it putting out a clean signal?

Thanks, Rich

Think about it. If it isn't clean, the echo won't be.

--
?

Michael A. Terrell
Central Florida

There are a couple of these in a cabinet in the back of my office. I checked today and one is a 5J29, like the one in this auction, and the other one is a 5J33, which is almost the same, except that there is an extra copper slab that sticks down from the center of the U.

As others have stated, these are all split anode magnetrons dating from just before WWII. The U-loop is the inductance, and the capacitance is between the blocks (there are 2 halves, each attached to one side of the U.) Together this L & C determine the output frequency.

There is a cylindrical cavity milled in the space between the 2 blocks and a filament runs thru that cavity. Electrons are accelerated as in a cyclotron and generate microwaves in the U-loop. The U-loop is extended outside the vacuum by straight pipes which are shorted together at an appropriate distance to tune the magnetron. Microwaves are coupled out of the system by a loop which is coupled to this external line.

There is a good explanaion of this at a British site. Google on "virtual Valve Museum" for more info.

-

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

-----------------------------------------------

I would appreciate that.

Thanks for the confirmation that 1) it *is* a magnetron, and 2) it is a two-anode maggie.

Paraphrase of Jimmy Cagney: "You dirty Copper!".