Re: Picture tube --> cap?

To: tesla-at-pupman-dot-com
Subject: Re: Picture tube --> cap?
From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
Date: Mon, 30 Sep 1996 11:42:39 -0500
>>From cfrancis-at-infinet-dot-comSun Sep 29 22:03:20 1996
>Date: Sun, 29 Sep 1996 17:57:15 -0400 (EDT)
>From: Chris Francis <cfrancis-at-infinet-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Picture tube --> cap?

       
>I was getting ready to pitch an old tv and started wondering...

>Would the picture tube make a good cap? (aside from the size and breakage
>potential.)

>It should be able to take the voltage.
>Anybody try this?

>Chris

Chris,

Some of the old tv's (and I'm assuming you're not referring to transvestites 
here) had a conductive coating of carbon on the outside of the bell 
which was to contact chassis ground through a spring, copper strap 
etc.  It would work the glass as a capacitor against the inside 
aquadag HV accelerator coating inside the tube, and be used as a DC 
storage/ripple filter for the set's HVDC power supply.  I think you 
will find that the distributed resistance of these deposited 
conductive films may hurt the pulse discharge current available from this tube
being used as a Tesla capacitor.  Before I attempted this test, I would 
carefully let air into the CRT by snapping off the evacuation stem at 
the base connector on the small end where the E-gun lives.  You don't 
want a large vacuum bomb exploding in your face if and (probably) 
when the bell glass punctures from thermal runaway.  You know how 
glass seems to be in Tesla use! : (.  Another way to safely introduce 
air is to use a very sharp pointed metal awl and work a hole into the 
middle of the recessed surface plug on the bell where the HV lead 
would normally attach.  This sheet metal here is really thin.  
CAUTION, always wear at least safety goggles when handling CRT's, 
especially large ones, and gloves and a leather coat or welder's 
apron if you have them while working on a giant glass vacuum vessel.
Always be gentle and avoid anything more than gentle pressure when 
working on one of these tubes.  The glass is already stressed 
enormously withstanding 15 PSI from atmosphere.

Even if this works, it will only be suitable for a relatively small 
coil and the resulting capacitor certainly will not win any awards 
for space efficiency.  But in the spirit of experimentation and 
finding new uses for discarded widgets I encourage you to try this 
experiment.  :-)

regards,

rwstephens