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Re: Museum Coil Revisited

Tesla List wrote:
> 
> 
> Tesla List wrote:
> >
> > > Subject: Re: Museum Coil Revisited
> >
> > Subscriber: rwstephens-at-headwaters-dot-com Tue Dec 31 09:26:10 1996
> > Date: Tue, 31 Dec 1996 03:57:13 -0500
> > From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: Museum Coil Revisited
> >
SNIP
> > I do wish to buzz MTC higher than 7 kVA soon however
> > and try to go for 4X the 50 inch resonator length in output spark
> > length instead of the only 3X it presently does.  I really think it
> > can!  I'd better try it soon though, Chuck Curran is up to something nearly
> > identical in secondary resonator size, but sporting considerably more inductance
> > and also thicker wire, and a significantly larger topload C.   I don't want to loose
> > my place. : )   Chuck, I haven't heard from you! : )  I spill my
> > construction secrets to you trying to help, and you hide.  Any hardware store
> > merchants on this list in Chuck's area, be on the lookout for sales of heavy guage
> > 200 foot extension cords!  : )  Look out Gerry LaBine!
> 

Robert:
	I didn't think I really had anything too out of the ordinary--100% of
my new coil specs have been already listed!  Yup, I hide--in the
basement working on the primary of late.  Just ask my wife.  She did get
me out on New Years eve though!
 >
 >From here on, with any further increases in power I'm going to have to
 > carefully watch the temperature of my stationary tungsten carbide
pads on the
 > rotary which are merely brazed onto their steel supports.  I don't
want to melt
 > the brazing.  These contacts are operated in high speed air blast
 > from a vacuum cleaner blower with two small directed nozzles for
 > cooling.  So far this has worked faultlessly with the tungsten, but
amazingly
 > DID NOT previously when the contact material was mild steel and all
 > other parameters including power level were identical!  My contacts
would go
 > into thermal runaway, incandesce, and vaporize in a steady shower of
sparks in
 > the blast air stream.  MTC's rotary break is run just like D.C. Cox's
unit, without    > any series quench gaps.
 >
 > I posted my ideas on this a while ago, postulating that
 > the tungsten could operate at a much higher surface temperature from
the
 > getgo without emitting a cloud of vapourized metal ions from its
 > surface, thus preventing the thermal runaway effect.  I believe a
 > very micro-thin pool of molten surface metal instantaneously develops
 > at the end of the switch arc with the steel contacts, and not so with
 > the flying thoriated tungsten/stationary tungsten-carbide interface I
now use.
 >
 	This situation does puzzle me right now.  I have had limited use of my
rotary at high power, but it sure has held up with no priblem in August
and September I was running regularly at over 6000 watts with no
noticeable electrode wear.  The rotary has 12 electrodes--each one is a
3/8-16 stud with 3/8" stainless acorn nuts on either end.  The two
stationary contacts are 1" diameter brass by 1 1/4" long with a taper on
the contact end leaving a 3/8 contact surface.  These are adjusted in
and out on 3/8" threaded rod about 4" long.  Lots of mass and it runs
pretty cool so far.  I effectively have 24 rotating electrodes for heat
absorbtion and the two big brass stationary electrodes that show some
erosion but only a few thousands deep.  I don't know, the new Simpson
analog meters showed a minimum of 20 amps(sometimes 34) at 300 VAC
coming out of the autotransformer Robert and the durn thing held up O.K.
with no cooling fans of any sort.  I'm wondering, are your carbide fixed
contacts/electrodes mounted on smaller diameter rod, less mass to absorb
heat??  Or maybe mine will just go into a delayed melt-down the first
time I fire it up this spring!  I better get back into the basement
now--gotta sand the primary form yet tonight prior to mounting the
primary acrylic supports.  Screwed them up the first time,just too long,
but now they are ready to mount too and then winding the 5/8/" tube. 
Text book coil design, nothing special :-)

Take Care,

Chuck Curran