Hole in magnetron end (melted) - how does this happen?

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RogueRose

Joined Oct 10, 2014
375
I took apart my old microwave and found the magnatron has a 6mm round hole burnt in the copper side/end of the tip. The copper cap is pretty thick too, IDK what gauge but it is pretty solid so there must have been a lot of energy to heat this. I noticed that things heat much faster in my newer microwave, maybe 20-30% faster and it is even rated at a lower wattage by 200w.

I did have an incident a month or so ago while heating a cup of water. There were arcs inside (not visible inside the oven area but noticeable through the venting holes). The inside was almost totally clean and no metal present. The fireproof fibrous shield over the magnetron had scorch marks and after removing it and cleaning it no more sparking. So I thought it was this material causing the sparks. Some posts say that grease on the material can cause this. Obviously seeing the hole made me think it was this copper end being burnt, now.

The inside was basically immaculately clean except for the exhaust fan blades had some dust, so IDK what could have caused this burn-out.

Anyone see this type of thing before?magnetron.jpg
 

SLK001

Joined Nov 29, 2011
1,548
Looks like a hot spot from a standing wave. Probably from operating said oven with nothing in the chamber - very bad things happen to the oven when that is done.
 

ian field

Joined Oct 27, 2012
6,539
Looks like a hot spot from a standing wave. Probably from operating said oven with nothing in the chamber - very bad things happen to the oven when that is done.
Years of subjecting microwave ovens to extreme abuse - never had that happen.

The angled top of the stub creates a corner - I suspect that's what caused the hot spot.
 
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