RE: 60kV 50MHz HV Divider Completed

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

Original poster: "Mccauley, Daniel H by way of Terry Fritz <teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>

 > Hi Dan,
 >
 > I couldn't tell from your schematic what type of caps were
 > used for the 82
 > pF compensation caps.  My assumption is that they are ceramic.

Yes, that is correct.  Both Vishay and AVX makes these type of high voltage
ceramic capacitors.  These particular
capacitors are rated 82pF at 10kVDC each.


 > I once attempted to build a purely capacitive HV divider, also using
 > ceramic caps on the HV side.  When I attempted to scope the
 > output of an
 > NST, the resulting voltage was grossly different than what
 > the capacitive
 > ratio should have produced.  I mentioned this on this List,
 > and I think it
 > was Bert Hickman who pointed out that ceramic dielectrics have an
 > unfortunate property of creating a capacitor that's voltage-dependant.

Actually, ceramic capacitors are pretty much the industry standard for
commercial high voltage dividers.  Almost all
your potted high voltage dividers will use these same type ceramic
capacitors.

 > This effect may be less evident if the dominant division is
 > achieved with
 > R's rather than C's, just something to keep in mind (and
 > something that
 > simulation models don't account for).

 > BTW, your Marx generator is BEAUTIFUL!  What did you use for the gap
 > electrodes?  Are the support plates for the electrodes
 > constructed so that
 > they are hinged and may be adjusted in unison?

Thanks.  The spark gap electrodes are the home depot special drawer knobs
which are standard issue at almost any
Home Depot and sell for price of $2.29 each.  (adds up considering i have 24
of them), but well worth it. I was going to
use standard one inch corona balls, but these seemed to mount much nicer in
they have nice flat flange on the back end to butte up against the support.

The spark gap assembly isn't hinged, but does have the bottom and top
support plates which can either be replaced with
longer plates, or spacers installed.  I could have made a hinged design, but
wanted something a little more permanent.  Initially it will be pain to fine
tune the gap widths, but in the long run it will prove worthwhile.

I'm finding out by tomorrow whether I'll be going to Kwajalein Missile Range
(Marshall Islands) for six months, but if I don't i'll definitely be
bringing the marx generator up to Rochester when I see you in August.  Just
beware, my minicoil is growing stronger every day!!!!

The Captain







 > Regards, Gary
 >
 >
 >
 >   -----Original Message-----
 > From: 	Tesla list [mailto:tesla-at-pupman-dot-com]
 > Sent:	Thursday, May 15, 2003 1:45 AM
 > To:	tesla-at-pupman-dot-com
 > Subject:	60kV 50MHz HV Divider Completed
 >
 > Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>"
 > <dhmccauley-at-spacecatlighting-dot-com>
 >
 > I finally got around to completing my 60kV High Voltage
 > Divider.  The design
 > works extremely well (from initial tests) and should serve as a good
 > baseline for others wanting to build hv dividers capable of
 > high frequency
 > measurements.  The frontend features a combination
 > resistive/capacitive
 > divider and
 > a additional box which attaches to the unit to allow fine
 > adjustments of the
 > gain/frequency compensation of the entire hv divider.
 >
 > http://www.spacecatlighting-dot-com/hv_divider.htm
 >
 > Specifications:
 > Maximum voltage:  40kV-60kV (construction dependent)
 > Bandwidth: 54MHz (simulated 3dB roll-off)
 >                     50MHz (measured using impedance analyzer)
 > Ratio: 1000:1
 >
 > Enjoy!
 >
 > The Captain
 >
 >