Posted this many times, and it's not just "nowadays"
I remember one time the magnetron started acting up in the GCA RADAR (NAS Miramar) Man!!! We turned to!!! Yanked the transmitter out of the bay and got it outta there while another tech roared over to the supply to dig out the spare. And........the.......spare.......was............no......damn......good. Of course it cost us a lot of time because we had a tough time convincing ourselves that was actually the problem, and not something else that we'd missed.