Greetings.
I would like to show a couple of pictures that I think will be of interest to all.

The first photograph is of a magnetron that I cut into two.
Had I known that they were made of copper, I would never have thrown away all faulty ones I had changed in the past.
Second point of interest is the internal construction. It is not like the diagrams of resonate cavity magnetrons that I have seen in text books.

There is not much that goes wrong with magnetrons. The only odd fault that I recall is of a magnetron that would not oscillate because one of the two magnets had a crack in it.

The second photograph shows three faulty capacitors.
The white capacitor is leaky, in this case putting a short across a resonate circuit, the second cap, an electrolytic, has a corroded positive lead. It is ALWAYS the positive lead that corrodes, never the negative lead. When supercaps first came out, I was sceptical that they were actually batteries. When I came across my first faulty one I removed it form the board, and, you guessed it. The positive lead was corroded.

The third cap. This is a new one to me. Brand new. Never used.
And yet, it has done a Chernobyl. It was alright when I put it into my parts draw.

Download the pictures and expand to see more clearly.

Wayne.

The plasma in that sort of magnetron, I believe rotates like a motor. The PHT is not exactly a modern cap. Its 70's & I am not sure if it is Polyester? The only one I have handy here in that style is marked MHT & is a UCC. It may have been a wrong fitment, as it is not leaking 500VDC.

Positive also gives trouble in batteries as it is the "hot" terminal, & likely why many old British cars used braided positive earth leads.

I had an 11-25 this week with an electrolytic cap leak like that. Still at a loss as to why it was still there when they changed the other one? Not the only error of judgement. Notwithstanding that Electrolytic caps do need a few volts after sitting for over a couple of years. There were a lot of Taiwanese origin caps of the 90's that were made with a stolen Japanese formula, that some smarty had left an essential chemical out of, just for the hackers benefit.

Pretty much, all of them did that and did millions of dollars worth of damage in the process. I have seen motherboards with them & most failed in warranty. All you had to do to see the Mother board fault was look at it and all the little embellishments, on top of the Electrolytic's.

Always a good idea to clean the resin off, some is corrosive & coat joints of dissimilar metals on coils.

Marc

Those white UCC ones are a common sight in old B&W TV's especially in applications requiring a working voltage in excess of 630v DC. I view these with much suspicion as they can be as leaky as old waxed paper capacitors. I have also had some that test fine and still work. I suspect they have either part polyester / part paper or all paper insulation.

One could speculate that the better jacket & sealing would have a direct bearing on the longevity of the cap. Do not however be complacent, I have seen several of the caramel coated polyesters of that era, crack like mud's especially if the fitter failed to put a kink in a wire as a strain reliever where the cap was likely to have very short wires.

This can happen with several & I have even had a Mica suffer similar fate in an IFT and a couple of SM's tear a chunk out of a board as they were placed in stress.

Marc