Microwave magnetrons keep failing
A year ago my GE microwave’s magnetron failed. I replaced it and it worked fine for a year and now I again have a short somewhere (loud hum then blows fuse). The magnetron resistances check out OK (<1ohm filament, no conduction to body), but then again, the old one that I had replaced also checked out OK this way, yet replacing it did fix the problem. Not seeing any arcing near the connector or at the antenna. The diode is fine (VF=9V, no cond. in reverse). The capacitor is fine (0.91uF, no shorts). Shorts in the transformer windings seem unlikely; I see no evidence of arcing or burning. Can’t be the door switch (the NC one), since if that was bad it would have blown the fuse immediately, not after a few seconds.
So it must be the magnetron again, but before I buy another replacement, any ideas why they keep failing?