Topband: Bad tower shunt capacitor

[Tom W8JI]

>I have an omega matched 120 foot tower and I apparently have a bad vacuum 
>variable capacitor. Upon applying more than about 300 watts, the SWR goes 
>off scale. Tuning it out and trying again, yields the same thing.
>
> The question is which capacitor is the culprit. These are surplus Soviet 
> caps obtained from the Ukraine and, as I recall, the larger value 
> capacitor is the parallel one, not the series one. I could buy one of each 
> and switch one at a time and have a spare left over. Any suggestions ?

Jamie,

How do you know it is a capacitor and not something else? Normally vacuum 
capacitors are either good, have air, or are shorted.

They short when a plate melts and stay shorted in that position or further 
meshed

They have no return pull tension when they have no vacuum

If the tuning is changing, maybe something else on the tower is arcing, like 
an insulator?