"Breaking-in" new radar magnetrons 2

[BrianG]

Has anyone out there heard of the need to break-in new magnetrons at reduced power for the first few hours? We recently experienced an early failure in a new radar being built in production, and the magnetron maker said it failed because we should not have used full power so soon!

 

[linacman]

It is usual to run in a new magnetron for a couple of hours at lower power levels, increasing the power level over the run in time. You want to minimize arcing as you get up to your normal operating levels.

 

[BrianG]

Thanks for the reply linacman.
We understand about the need to avoid arcing, but we believed that the magnetrons had at least been partly burnt-in by the manufacturer. I don't think we have been given any specific instrcutions by the manufacturer for burn-in, so the question is how do you know if you are pushing too hard too soon during initial test? Does your usual supplier give you a recommended burn-in power profile?

 

[Markone]

typicaly the magnetron would have been run in by the manufacturer, however this is not going to be in yuor system, so some ageing in your system could be required if this is done by operating at levels where no arcing occurs progresivly incresing the level, but backing it off if arcing occurse you should be able to rapidly get to full power operation

 

[hacksaw]

any high power tube needs to be run up slowly the first time

 

[linacman]

You're welcome, BrianG. I'm happy to toss in my two cents worth.

Our maggie supplier states in their documentation:

"It may be desirable to operate the magnetron initially under reduced input conditions to clean up any gas that may be present and so reduce the risk of excessive arcing. This is particularly important when the magnetron has not been in service for an appreciable time."

So I read that to say that even though they are "run-in" at the factory, after they have been sitting around for a while, they need to be run-in again when put into service.

Regards
linacman

 

[BrianG]

Hi linacman,
Yes, I agree with your comment about magnetrons that have been idle for a while, but in this particular case the magnetron had been delivered hot foot from the manufacturer's production line (late again on delivery!) and fitted straight into our equipment. It then failed unexpectedly after about 10 hours, so my original question remains; how long is reasonable for running in?

 

[linacman]

Hi BrianG

If it ran OK for ten hours, then you did OK at running it in. I have always used the "drive it until it arcs and then back off approach" After about two high voltage hours we usually find the thing is happy to be at the power level we require. There may be the odd arc for the next couple of HV hours.

For a sudden failure like you describe, your supplier owes you a new one. I only recall one such failure in my experience (of about 50 magnetrons). You probably have a 50 HV hour full-replacement warranty. Don't let them try to blame you.

Regards

linacman