Vacuum Variable---- Something Missing Part 2 pics

[N7ZDR]

Here are some more pics

What does the threaded crew do?

[W7TFO]

The screw pulls the bellows out to lower the uuF.  It has to hold it at the value you set it to, and usually there is a turns counter associated for easy resets.

With the wooden parts, something is definitely ersatz so I'd dig around for the real stuff.

73DG

[N2DTS]

The screw pulls the bellows out.
Someone made an insulated (wood?) mount for it, the stock setup has a metal end cap with the screw drive in it, and you would need an insulated mounting bracket for some applications.

[N7ZDR]

Lets see if I got this right---as you turn the crank handle the insulator slides between the opening pulling or pushing on the bellows.
That's the reason why the bolts were loose connecting the wood spacers together.

It looks like the first thing I need to find is a long bolt (all thread) to eliminate that small steel wire?? Does anyone know what the thread size is?

FYI---The inductor in this thing is the size of a 2 liter soda bottle. I think I made a good find

Regards
Larry

[W1ITT]

The thread on that vacuum variable actuator is probably  1/4-28, not the more common 1/4-20.  If you go to your local hardware store you can buy a 1/4-28 nut and check it for fit.  I have also seen some of the larger units with some variety of 5/16 diameter.  If it's one of the European or Russian units it may have a metric thread, but the unit in the picture looks like a good old Jennings Unit.
To see if it still has good vacuum, screw the threaded piece in a few turns then, carefully holding the capacitor in one hand and the actuator in the other, give a strong straight pull and see if the bellows works well.  It should require a manly effort.  If it moves easily in a  woossy fashion, the vacuum is lost.
McMaster.com will have the correct threaded rod once you confirm your needs.

[KD6VXI]

Delrin or nylon allthread makes a dandy threaded insulator if you want to keep the shaft insulated 

--Shane
KD6VXI

[N2DTS]

Vacuum pulls it closed, and the screw pulls it open.
There can be a bit of force on the screw, so I would likely use metal and an insulated shaft coupler.

Not sure its bolt thread but a worm drive thread, not the same....

[Opcom]

the thin wire and T bar is probably original. The wire is to be pulled straight and not cock-eye the capacitor element.

[WBear2GCR]

If you search online for images of Jennings Vacuum variable capacitors you'll likely see a number of similar units with proper adjustment parts on them. You may even find a site that shows an "exploded" parts view, so you can see how they normally work it.

If I recall, the shaft usually has a thrust bearing and when you turn the end (the knob end) the shaft rotates and
pulls the bellows... no telling what that gizmo on the end is supposed to do. But you have the "Rube Goldberg" unit in front of you, it's really hard to tell what's going on from the pix.

                       _-_-

[N7ZDR]

Thank You for all the great replies. This is one of them items will soon be a long lost art. This has really turned into a thread full of great information.
The first thing I did after work was screw it back on and give it a tug    yup she Finley broke loose at about 10 pounds of pull and quickly returned back. Looks like it still good. Now I just need get rid of the Joe Magee contraption it was hooked to. Will need to find a longer bolt (it appears to a a 6x32) and shaft.
Again--- Thanks all
73
Larry

[flintstone mop]

I think the cap is a gonner. Once that screw lets loose the bellows snap and will never be able to reattach.
TRUE? or FALSE??
I think that the cap is even damaged in this trauma.

[Opcom]

seems I saw a cap like that in an old Collins tuner 180L? - goes with an HF aircraft set. There was a srew wit a wedge pulled by a motor or some arrangement like it.

[flintstone mop]

I have motorized two vac variables for remote tuning of a special designed magnetic loop antenna, using a helical winding of a copper strip about 3" wide, instead of the solid copper pipe.
I forget the exact direction where the motor will stall out and no harm to the vac variable. Probably the bellows closed, max capacitance. The opposite direction the remote motor will continually keep turning, unless the designer installs a limit switch to stop the tuning before the screw lets loose. This is using a 12vdc 30 RPM motor as the tuner control. The concept is simple. As the bellows are extended for min capacitance, the shaft of the vac variable cap will push against the tuner motor. And by mounting a micro-switch on a tin mounting plate that is supporting the tuning motor, will open the DC voltage and stop the motor before the screw lets loose.