Vacuum Variable

[K9ACT]

I have been plagued with arcing on my 8000 rig and about to give up trying to find a suitable air variable.

Seems like a vacuum variable would be a good option but I am not at all clear on how they work.

A friend said to make sure the one you buy comes with a "puller".  I have spent at least an hour trying to find info on such a device and find nothing.

All the caps I have been looking at have 1/4" shafts and I have been assuming that turning this shaft changes the capacitance like any other cap.

Not so says my friend... you have to pull on the shaft.

I saw one that actually says it has a rotating shaft for cap adjustment.

Could someone clear this up for me.

Here is a link to one that would seem to do the job.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=390012738246

The seller has not responded to email so I would by one elsewhere but does this type require a "puller"?

js

[Opcom]

The puller is the metal cylinder thing on the front that the shaft comes out of. Inside the thing, the shaft is threaded and there is a nut, so that as you turn the shaft, it pulls the 'plates' apart inside the evacuated container. A bellows on the front of the container, insidethe 'puller' as he is calling it, allows this in and out motion.

http://www.altavista.com/image/results?itag=ody&q=vacuum+variable+capacitor&mik=photo&mik=graphic&mip=all&mis=all&miwxh=all

[K1JJ]

Jack,

Pat did a good job of describing the puller function.  ( I deleted my duplicate info)

Yes, vac caps are the way to go. I don't use bread slicers here anymore except for low level input circuits.


T

[k7yoo]

If you need a Vacuum variable get in contact with me and I will bring it to the Stoughton fest. How many pf? 300-500?
BTW I have the turns counter & "puller" This is a new one on me!!
Skip
k7yoo@yahoo.com

[Opcom]

it makes me want to cry, now I remembered the day a 2000pF 15KV glass vac var rolled off a desk and splatted on the floor. The untimate loading capacitor.

[flintstone mop]

Just be careful with "the puller" or shaft....It will be hot with RF!!!

Fred

[WA1GFZ]

usually you ground the shaft end unless the whole thing is floating then you need an insulated shaft coupler.