From: email@example.com (N. Thornton)
Subject: Re: In Need of a 50-KV Electron-Gun
Date: 24 Oct 2002 17:55:09 -0700
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: 25 Oct 2002 00:55:09 GMT
firstname.lastname@example.org (Murat Ozer) wrote in message news:<email@example.com>...
> firstname.lastname@example.org (N. Thornton) wrote in message news:...
> > Alan wrote...
> > > 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
> > electrically tied.
> Murat: The target is required to be at 0 V. The electrons need to be
> accelerated to +50 KV. So, would applying +50 KV to the accelerating
> anode while applying no voltage to the cathode do the job?
The e-beam is accelerated as far as the +50kV 'trode, but then it has
to travel from the +50kV trode to the 0v target: and that will
decelerate the beam back to minimal. So that wont work. If your target
must be at 0v, then logically your gun must be at -50kV.
BUT there is a probablw workaround. Now do check this with someone
before taking my word for it, this is what I believe is so: If one
places an open grid near the target, grid at +50kV, as well as the
+50kV trode nearer the gun, the ebeam will accelerate to the first
50Kv anode, then maintain constant speed as it moves towards the 50Kv
grid, but between grid and target it will only slow to a limited
extent. You end up with most of you +50kV speed, yet a target at 0v.
But please do check this before building anything. There are people
with more intricate knowledge of valves (tubes), you might want to
crosspost to rec.aniques.audio+phono too.