Re: Fritz vs TCBOR -- initial results in...

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

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

Tesla list wrote:
 >
 > Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
 >
 > Hi Ed,
 >
 > I expect you've probably looked at this gap in some detail. Can you share
 > any other details about it? I've been meaning to build something similar. I
 > have about 100 square brass sheets (1.5" x 1.5" x .01") which are perfectly
 > precut. I'm not sure where I picked these up at, but when I saw them, I
 > immediately thought of the old quench gaps. I'm sort of curious on gap
 > spacing. What I've imagined is building 1000V sections where sections could
 > be series'd for higher breakdown potentials. I'm sort of curious on the
 > size of the inner hole (I would think a small hole would be sufficient and
 > beneficial to quickly evacuate the breakdown cavity quickly). I think for
 > mechanical ease and electrical adjustment, series'd sections would be the
 > way to go on something like this.
 >
 > Thanks,
 > Bart

	I have some pictures I took which I could sent you now (may have posted
them in the archives but can't remember), but they are all external
views.  I might be able to find a description of the construction of
this particular gap in an old QST magazine and I'm sure I have quite a
bit of information in old books.  Question of digging it out and
copying.  [I'll try to ignore the legality of that, but when something
has been out of print for 80 years I don't think anyone is guarding its
copying with any energy.]

	If I had the ambition, which I don't at the moment, I could take the
thing apart and take pictures of the construction of the plates and also
measure the gap dimensions more carefully than I have.  Based on faulty
memory the size of the SPARKING electrodes is pretty close to an inch in
diameter but the overall dimensions of the copper plates in which
they're mounted are about 4" by 4", to facilitate air cooling.  I think
I guessed that the separation between the electrodes (air gap, in other
words) is about 0.010" but that part I'd have to check more carefully.
In any event, I think the original spacing was greater but that the
fiber insulating washers have become significantly flattened over the
years.  The basic construction is that of a stack of copper plates with
protruding electrodes on each face, separated by fiber washers and the
whole thing put under compression (lots of it!) to make it air tight.
[Note that the cavities are NOT evacuated, but contain residual air from
which the oxygen has been deleted.  In other words, mostly nitrogen at
slightly less than atmospheric pressure.  I'm sure the air leaks back in
slowly but the oxygen keeps getting removed.] The thickness of the
insulating washers is selected to set the gap width.  What I'm really
having trouble remembering is whether the sparking surfaces are integral
with the plates, or whether they are thicker material inserted into it.
I have seem a number of construction articles in which the author
described machining a plate to produce the individual sections, which
seems incredibly hard to me.  Cutting metal off the flat part of a big
copper plate sounds to me like a really difficult and potentialy
disappointing project?  One thing I forgot to mention is that the
cooling plates actually have a little trough around the edges of the
electrodes to keep the spark from walking over to the fiber!  Someone
must have had a neat manufacturing and assembly technique as these
things were ground out by the thousands for use in
WW1.

	I've printed your note and posted it in the "things to do next" file.
It takes about half a day to take this thing apart, separate the pieces,
take the pictures and measure the dimensions, and then reassemble it.
Also takes a special jig consisting of four steel rods stuck into a
plate over which the individaul plates are strong, with washers in
between.  The plates have holes in them for this purpose.

	While I'm at it I remember corresponding on this list with someone in
England (five years ago?)  who had built some gaps on his own.  Maybe he
can step forward and repost his works?

Ed