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725A

 
    
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The picture of type 725A is deceptive in that most of what is shown is the pulser and pulse transformer. Only the black disc at the top is the magnetron. The cathode stem of the magnetron cannot be seen because it projects downwards into the (oil-filled?) well of the pulser casing below. Also deceptive is the fact that the most massive part of the assembly, ie. the magnet, is missing. This fits over and round the hub of the magnetron disc.
The magnet is an essential part of the magnetron without which the latter cannot operate. Magnetron and magnet have to be closely matched and are normally designed as a pair although with many types at the end of life a replacement magnetron can be fitted into the old magnet.
Type 725A is a WWII X-Band magnetron operating in the frequency range 9345 to 9405 MHz. Its rated peak output power is 40 kW but this corresponds to an average RF output around 50W. Pretty puny but sufficient for a radar-directed gun.
The RF power is taken out of the valve via a probe into the waveguide. Shown at top right.
The dimensions of the assembly are 178 x 190 x 210 mm.
References: Datasheet.

 

Absolute Maximum Operating Conditions
Magnetron
Vh
Ah
Va
mAa
6.3
1.0
16,000
16,000
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated December05, 2012.
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