Hi, if you are certain the magnetron is at fault contact me via microwave-repairs.co.uk You will need to supply the machines make and model details, or at least the model code from the magnetron. Caution here if you are getting involved in the guts of a machine. Magnetrons run at four thousand volts and machines have been know to store high voltage power in the drive circuit for many months, and are still lethal, so take great care.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix microwaves.