Western Electric JAN 725A Pulsed Magnetron
Magnétron en régime pulsé
Impuls-Magnetron

A waveguide-output, external magnet magnetron, fixed-tuned at 9375 MHz. Output was 55 kW. Was interchangeable with 2J21. Used in Philco AN/APS-15 bombing bradar, APS-6, etc. Same as 4J50 except it had smaller magnets to reduce size. Manufactured by WE and Northern Electric. Raytheon made a 725A but redesigned the resonator system to use a vane-type structure which was more adapted to their manufacturing practice.

The 725A became one of the most extensively manufactured tubes, numbering over 300,000 among these three plants. This design led to the matrix cathode, as opposed to the sprayed-oxide cathode. In the first version, the finely divided nickel and Ba-Sr carbonates were mixed and applied and then held in place by a nickel mesh. The final version consisted of a coarse nickel powder and carbonates. The mixture was sintered onto the surface of a machined nickel cathode. This extended tube life from tens of hours to several thousands.

Fiche technique • Data sheet • Datenblatt: 725-A.pdf

 

83 x 140 x 153 mm • 3" 1/4 x 5" 1/2 x 6"

A view of a cut-away 725A magnetron. Note the breaks in the double ring straps, the so-called “halo” loop above the hole of the output resonator, the step in the center conductor of the output coaxial providing the necessary impedance transformation, and the details of the coaxial to wave guide junction.

725A cathode construction. Shown are:
(1) the heater element;
(2) the machined nickel cathode blank;
(3) the cathode blank with the nickel wire mesh, welded or sintered in place;
(4) the mesh type cathode with oxide coating applied, cut away to show heater element in place;
(5) the more recent cathode with sintered, nickel powder, matrix base (uncoated).

 

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