[TowerTalk] Jenning Capactior question

[Tower]

> What I found is that instead I rotate the shaft there is no
> change at the capacitance. Is this normal, maybe because
> it´s the cap by itself?>>
>
> If you grasp the capacitor body firmly and pull outward hard
> on the blue area, the blue area should move outward like
> working against a spring. That is the air trying to close
> the bellows because of the vacuum in the capacitor. If it
> does not do that, you may not have vacuum in the capacitor.

It should still change capacity though.

In normal use the blue area (cone) what ever you call it, sets on the end of 
the cap.  There should be a threaded rod through the cap with a tiny thrust 
bearing on the end of the cap so the screw (usually 1/4 28 as I recall) 
pulls against the cap and pulls the one half of the inside toward the cap.

As Tom says, it feels like a pretty strong spring.

Even with one that has lost the vacuum it should still be springy, but it'll 
stay pretty much where you put it.

I had some *big* Jennings around here for a while.  Bout 14 to 16 inches 
long and near 6 inches in diameter with a 20 KV rating.

Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
www.rogerhalstead.com

>
> If you turn counter clockwise when the capacitor is fully
> maximum the lead screw unscrews and the blue area gets
> loose, and nothing changes with capacitance. If you turn
> clockwise on the shaft many turns, the screw slowly pulls
> the bellows out against the air pressure and the capacitance
> slowly decreases.
>
> 73 Tom
>
>
>
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