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ID = 77754
Tube type:  Pulse magnetron   SHF/EHF (>3 GHz) 
  Ca. 1925 up to 1945 rare.
Identical to 2J21
Successor Tubes 2J36   2J21A   725A  

Was used by Radar
Filament Vf 6.3 Volts / If 1.3 Ampere / Half indirect

2J21 was the first 3-cm pulse magnetron to be produced in volume. Starting from the 10-cm design, scaled-down prototypes with 18 slots were operated at MIT since the summer in 1941. They gave power peaks in the order of 5 kW but were unstable, generating a confusion of modes. Westinghouse, with the active support of the Columbia University, improved the design reducing the cavities to 12. The resulting magnetron, still unstrapped, was capable of delivering about 10 to 15 kW with an efficiency from 12 to 15 per cent.

The 2J21 was delivered from1941 and discontinued in 1942, replaced by the improved 2J21A and soon later by the 725A. As far as we know, it was only used in the early production of RT-10/APS-3 X-band airborne radar.

Registered to Westinghouse only in December 1945, after the end of war and when it was definitely obsolete.

Information source -- Original-techn. papers.   
-- Collector info (Sammler)   
2J21: Private collection
Emilio Ciardiello


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