From: email@example.com (N. Thornton)
Subject: Re: In Need of a 50-KV Electron-Gun
Date: 23 Oct 2002 08:07:37 -0700
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
NNTP-Posting-Date: 23 Oct 2002 15:07:37 GMT
> In normal operation the HV is applied only to the conductive coating
>on the inside of the glass bulb. The highest voltage on the actual
>of color tubes is the approx. 5 kV focus voltage.
OK. So how about running it on its usual 5kV plus adding a separate
50kV accelerating electrode? This is after all sort of how the CRT gun
is designed 2b used. A ring shaped trode would presumably be suitable,
at sufficient distance to avoid arcing. I may be off track... but if
so can you tell me why?
> Instead of trying to remove the gun from an existing CRT, why not buy
>a replacement gun from a CRT rebuilder who rebuilds monochrome tubes?
> Unless the target is very well insulated the gun will have to be run
>at -50kV, which presents major insulation problems for the gun and
>voltage power supplies.
> Regards, Alan.
Presumably either the target is at +50kV, or the gun assembly is at
-50kV, or possibly a grid near to the target is at +50kV but the
target isn't. Either way, its not going 2b substantially different
with a CRT gun than with a more specialist gun. Bear in mind many of
the electrodes would be irrelevant on a CRT gun and could simply be
email@example.com (Rich Grise) wrote in message news:
> firstname.lastname@example.org (Murat Ozer) wrote in message news:
> > email@example.com (N. Thornton) wrote in message news:
> > > firstname.lastname@example.org (Murat Ozer) wrote in message news:
> > > > Hello,
> > > > A friend of mine from Mt. Vernon, Washington is preparing a vacuum
> > > > scattering experiment. He has the vacuum chamber, the pump and
> > > > everything else. The 50-KV electron-gun needed in the experiment was
> > > > lent to him by another friend; but it does not seem to be working. We
> > > > have searched the Internet to find e-gun manufacturers. The guns of
> > > > Kimballphysics are too sophisticated and has astronomical prices. We
> > > > need a simple gun (like those used in oscilloscopes) that will work at
> > > > 50 KV and less (anode-cathode)voltages capable of producing a spot
> > > > (1-2 mm diameter) on a phosphor screen at distances from 30-75 cms. No
> > > > varying current or other functions are necessary. It should have a
> > > > flange with screws to mount it on the vacuum chamber.
> > > > We need your help...
> The only real shortcoming I can think of in using an existing
> electron gun from a TV or scope tube is, well, a couple of them,
> actually - breaking the glass and somehow attaching the glass
> shards to your experiment; pumping it down to a really, really
> hard vacuum after the gun's been in air, and the glass is welded;
Perhaps we can get those 2 in one move. How about...
Attach tubing to the CRT's seal nipple, evacuate the tubing, connect
tubing to a protective gas container (ie no oxygen or water vapour).
Now break the CRT nipple, and CRT fills with protective gas.
Now one can weld glass onto the neck using a piece of glass from
another CRT and a blowtorch / bunsen / etc.
Finally the thing can be cut and handled however a 50kV gun is usually
> driving it with the right voltages, including your makeshift
Really its the focus voltage one would need to supply. Most of the
other trodes can be tied. When the control electrodes arent being
given negative voltage, it would probably be poss for other control
trodes to be tied to 0v instead of +. That often works. If not, a
+400v supply is not so tough.
> designing focusing coils and an ion trap -
Electrostatic focussing is already built in. Focus Vs on modern TVs
are typ a few kV for colour or a few 100s of V for B&W. Nothing
Ion trap is already built in and working.
> in other words,
> it's doable, but an incredible pain in the ass. Either way, whether
> you buy, build, or salvage.
I think its easier than you say - but whatever approach one uses is
going to be a fair amount of work, TV gun or specialist microscope
Now, praps someone can tell me where I've gone hopelessly wrong :)