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Re: Gaps

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> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: Gaps
> Date: Saturday, February 01, 1997 1:15 AM
> 
> Subscriber: SSNSanders-at-aol-dot-com Fri Jan 31 22:52:50 1997
> Date: Fri, 31 Jan 1997 08:32:02 -0500 (EST)
> From: SSNSanders-at-aol-dot-com
> To: Tesla-at-pupman-dot-com
> Subject: Gaps
> 
> My gap is a series of brass drawer pulls and its just too much
aggravation to
> keep it clean. They carbon up quickly and have to be sanded then reset. I
> read about a gap Tesla made, something on the order of two blocks of
metal
> with holes drilled in such a way as to cause them to draw air through
them
> when they started heating and it keeps them fairly cool. They are set
close
> together and I believe he wrote that they functioned very well. Is anyone
> familliar with the design? If I can I would like to try it or if needed
have
> a machine shop mill some out.    Stephen Sanders

Stephen,
Thomas Stanley Curtis describes a spark gap somewhat similar to what you
are talking about in his book HIGH FREQUENCY APPARATUS available from
Lindsay Publications.It was originally published in 1916.

Mr. Curtis describes what he calls a Quenched Gap beginning on page 41. It
consists of two LARGE, Heavy, Thick, pieces of metal that are cylindrical
in shape, with the facing ends ground and polished flat. The machined ends
are then placed from 1/1000 to 1/100 of an inch apart. Due to the massive
way it is built it can sink a fair amount of heat. This keeps the
electrodes cool and allows for hundreds to thousands of individual
discharges per AC cycle. This does not affect the resonant frequency, but
does affect the nature of the discharge from the secondary. Mr. Curtis is
lavish in his praise of this spark gap over all other types. He says it
produces a series of "very short, clean, and nearly undamped surges". He
mentions that as it heats up it deteriorates in performance. Today we would
probably force air cool the device. It appears from the description that
there is no need to force air THROUGH the gaps. (They are very close
together!)

By the way, these things were quite heavy and massive, with face diameters
of three inches and more, and thicknesses of about an inch and a half
(minimum), and greater. The sheer mass causes the heat to be removed
rapidly. The large parallel surface area allows for MANY conduction paths,
and thus high RF currents.

I do not have the facilities here to machine such a beast, but there may be
some of you out there who have access to such machinery as large lathes,
etc.  Does anyone know if any Coiler has built such a quenched gap and
reported on its performance? 

I saw a picture on the web recently of one very large coil that showed
something of the spark gap, and it looked a lot like what Curtis described.
It appeared to be convection air cooled. I wonder if, for continuous
operation it could be oil cooled or force-air cooled? Any one out there
have any further info on this?

Another form of spark gap that I have been thinking about would be an
offshoot of the Tesla Blower (The flip side of his Tesla Turbine). It would
consist of a fixed smooth circular plate and a rotating smooth circular
plate in very close proximity. The fixed plate would have a large hole at
its center (it may also use several smaller holes. The idea is to allow a
large quantity of air to flow)

When the rotary plate is spun at fairly high velocities, it causes air to
be sucked in from the stationary plate's center hole and then the air
travels in a kind of spiral out to the periphery. It uses the viscosity of
the air to effect the massive air pumping action. If the two plates are
insulated from one another and from the motor that is rotating the moving
plate, then they may be used to form the two electrodes of a spark gap.
Such a spark gap would have a very large surface area, and the air flow
would not only cool the plates, but it would also break up the sparks and
move them towards the periphery. I would imagine that at very high
velocities this would make an excellent quenched gap for continuous
operation! Personally, I would machine the fixed plate so that the inner
face was slightly further away from the rotating plate for the first inch
or so after the input air hole. This would tend to concentrate spark
formation further towards the periphery, where air flow will be faster and
therefore at greater pressure. The Tesla Blower hybrid is well within the
reach of some experimenters on this list. 

Fr. Tom McGahee