Re: differential probes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Ken,

At 09:53 PM 7/13/2003 -0500, you wrote:
>On Sun, 13 Jul 2003, Tesla list wrote:
>
> > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
> >
> > Hi Jimmy, Finn, and All,
> >
> > This is the present schematic and parts list I have in mind for the
> > differential probe.  I have NOT assembled or tested it yet!
> >
> > http://hot-streamer-dot-com/temp/DiffProbe-5.gif
> >
> > http://hot-streamer-dot-com/temp/DiffProbe-5p.gif
> >
> > It is still just using the basic 150MHz TI  THS4151ID differential
> > amplifier IC and other straight forward parts.
> >
> > One thing I am "trying" to add is a front end that can take a hard hit.  I
> > will have a system ground stud and MOVs at 1800 volts each.  These will be
> > fused with low current but high voltage fuses.  The idea is if you get a
> > say 20,000 volt cap on the input, the MOVs will clamp it and the fuses will
>
>How about some neon lamps or one of those glass or ceramic tubes the size
>of a pencil eraser with metal leads? Both should have a low capacitance,
>and don't conduct until 70 volts or so for neon, and several thousand for
>the larger ones. Maybe put them both in parallel. You probably want the
>lowest possible impedance in a short mode, otherwise the probe or what's
>left of it will dissipate lots of heat, which leads to it blowing up or
>catching on fire. Large energy storage caps are designed this way- to
>short out with the lowest impedance so their energy is dissipated outside
>the cap tank in bussbar and fuses, not inside where the tank will build up
>pressure and rupture. MOVs are basically firestarting kits.
>
>KEN


I have a "bunch" of Victoreen SGCA-2500D spark gaps:

http://hot-streamer-dot-com/temp/P7130038.jpg

The 2500 volt firing voltage is sort of high.  But not a big deal here if I 
put them in parallel with the MOVs...  I am hoping the "fuses" will break 
the current before any fires start...

Jim also mentions the Sidactors.  I think I remember of few of them blowing 
up in my face in the early 90'S :o))  But they are also another great 
possibility in this case!!

Cheers,

         Terry