RE: vacuum tube construction. (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 22 Aug 2007 20:42:56 -0400
From: Jeff Fink <revtec@xxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: vacuum tube construction. (fwd)

First, I would like to thank Frank and others for their kind and generous
response to my initial post.

I am presently collecting some equipment for some discharge experiments
aimed at producing short duration unidirectional pulses. I have a 9kv 60ma
Magnetek NST.  I want to assemble a full wave bridge rectifier by putting
1kv 6A diodes in series.  (It seems that 20 diodes per leg will give me
sufficient margin.) This will charge a 3000 pf 40kv doorknob capacitor that
I just got on ebay on the 20th of Aug.  The cap will have a series of 3 7.5
meg 10 kv resistors installed as bleeders across the cap.  The cap will be
mounted axially on the end of a brass assembly serving as the positive
electrode of a spark gap. The negative electrode will be a foot long piece
of 3/8 threaded brass rod.  The tail end of this rod will be wired back to
the bridge rectifier.  A pair of rare earth button magnets will be placed on
either side of the SG to rapidly extinguish the arc.  I plan to power the
rig off a 2KVA variac.  Initial tests will be ungrounded.  I understand that
connecting the high voltage side of this apparatus to house ground is a no
no.

It seems that the SG should fire on every half cycle.  

My initial goal is to see some kind of discharge off the threaded rod.

Do those with HV experience see any flaw in this plan?

Will the cap stand up to this duty?  The only markings on it are:

272Z
40kv
202A



-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx] 
Sent: Monday, August 13, 2007 3:28 PM
To: tesla@xxxxxxxxxx
Subject: RE: vacuum tube construction. (fwd)


---------- Forwarded message ----------
Date: Mon, 13 Aug 2007 12:13:06 -0700
From: Frank <fxrays@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: RE: vacuum tube construction. (fwd)

All this tube is is a simple Geissler tube.
The vacuum levels are not high enough to ever generate X rays.
You need a hard vacuum and a diffusion or turbine pump along with a 
scavenging method to pump the tube down hard enough to be able to 
generate X rays.  Tubes that can be taken apart for cleaning will not 
have seals good enough to hold an X ray vacuum.
Since the tube conducts, it will not work as a spark gap at all, 
basically it is a neon tube type effect and it will just glow as the 
voltage is applied and then turn into a voltage regulator and get 
brighter with more current until the electrodes start to get hot and 
they will out gas and lower the vacuum until the tube stops conducting.

Large mercury arc rectifiers will work as a switch with some 
additional circuitry but are not available anymore. Those were used 
on some of the early wireless transmitters.

Dosimeters are a device to measure radiation over time, basically a 
charged capacitor that is discharged by radiation. Usually they are 
calibrated in REMS and if they ever register, the amount of radiation 
is enormous and you better run!

A CD Geiger counter, Model CDV 700-XX is a good counter to measure 
radiation in small amounts and can be used to detect X rays. These 
are on Ebay all the time.

Frank

>Quoting Tesla list <tesla@xxxxxxxxxx>:
>
> >
> > ---------- Forwarded message ----------
> > Date: Mon, 13 Aug 2007 07:52:30 -0400
> > From: Jeff Fink <revtec@xxxxxxx>
> > To: 'Tesla list' <tesla@xxxxxxxxxx>
> > Subject: RE: vacuum tube construction. (fwd)
> >
> > I am new to this list and ironically this is the first post I have read.
> >
> > Over the years I have been experimenting with massive cold cathode
vacuum
> > tube diodes, looking at the phenomena of PAGD (pulsed abnormal glow
> > discharge).  I was wondering if the tube could be used as the 
> spark gap on a
> > TC.  I understand there could be X-ray production, but would it be
> > dangerous?  Another question: Would the X-rays register on 60's vintage
> > Civil Defense radiation dosimeters?
> >
> > My tube design is incredibly easy to build when you consider that there
is
> > no grid or filament, though some machine shop work is 
> required.  They can be
> > easily disassembled for cleaning and modification.
> >
> > My largest is 12" diameter, using a 12" by 3" long by 1/2" wall 
> pyrex tube.
> >
> > The anode and cathode are 3/4" aluminum plates.  The tube sets into a
> > circular groove on each plate and is sealed with a 3/16" O'rings 
> coated with
> > vacuum grease.  A hole and fitting on the cathode plate provides
connection
> > to a refrigeration vacuum pump sold by Grainger, which developes 
> a very nice
> > vacuum.  The tube lights off on only 600 volts.
> >
> > Jeff
>
>It wouldn't work so well for a TC because TCs have discharge currents in
the
>hundreds to thousands of amps and I don't think a discharge tube would
handle
>that too well for long. Also the 600V firing is kind of low so you
>wouldn't get
>much energy output from the coil.



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