Re: async rotory gap?

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

Original poster: "Luc by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ludev-at-videotron.ca>

Hi Duncan

I'm not sure if it's Tesla but I saw plan for a similar gap using
smaller copper disk If I find it I'll post the reference to the plan.

Luc Benard

Tesla list wrote:
> 
> Original poster: "Dr. Duncan Cadd by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>
> 
> Hi Bart, David, All!
> 
> >As you know, with a sync gap we have the ability to fire the gap at
> >concentric points along the AC cycle. The async of course cannot
> >sync and therefore will fire at good and not so good points along
> >the AC cycle. There are a couple basic async gaps. One is an AC
> >motor. This will run at something like 1750 or 3450 rpm's. The other
> >would be a DC motor. The DC motor has the ability to run at
> >variable speeds as a function of input voltage. With DC, you get to
> >play around with the break rates and can find break rates which
> >please spark growth. With the AC motor, you would need to build a
> >circuit to perform this function.
> >
> >I've run all three types.
> <snip>
> 
> There is one further variety, which AFAIK has not seen service since
> Marconi, but maybe there's someone out there who has done it and can
> comment, and I'm posting this in the hope they will step forth and do
> so!  It would be a particularly neat project for 2001 as it was the
> device used in the first successful transatlantic transmission a
> century ago.
> 
> The main problem which the rotary was designed to cure is quenching at
> high power, i.e. the prevention of continuous arc formation.  Whilst
> the rotaries used by most (all?) these days use fixed and flying
> electrodes, which limit the discharges to specific points on the
> timing cycle (or pseudo-random if asynch) Marconi's original idea,
> used in the Poldhu transmitter 100 years ago (the infamous
> transatlantic "S" signal) was to use two (or more) rapidly rotating
> disks spaced a short distance apart, their axes at right angles, with
> the spark taking place between the rims of the disks.
> 
> In this way, from one moment to the next, the spark was taking place
> from a cool metal surface, all the rest of the disk periphery where
> there was no spark was of course cooling quite nicely due to its rapid
> rotation through the air and also its considerable heatsinking ability
> to the main mass of metal.  There was also considerable amounts of
> cold air being propelled through the sparking zone by friction of the
> air with the disk, rather like a centrifugal fan (or even Tesla
> turbine!)  The spark length was adjusted exactly as for a standard
> static gap by the spacing of the disk rims, and the timing of the
> discharges would be just the same as for a static gap.
> 
> I wonder if anyone has tried this with a TC?  In "wireless" service it
> was good for a few hundred kVA with steel disks around a metre across
> and half an inch thick, so a one foot diameter disk should be good for
> a fair few kVA.  The rotary-with-electrodes was only introduced
> apparently because the radio waves generated by the smooth disks were
> insufficiently distinguishable from natural static to give optimum
> reception and the "characteristic rasping tone" from the
> rotary-with-electrodes (especially the synch rotary and a 400 or
> 800c/s power supply) which all TC builders know and love was much more
> identifiable to the wireless op's ears.
> 
> More trivia at:
> http://home.freeuk-dot-net/dunckx/wireless/sparksnarcs/sparksnarcs.html
> 
> Dunckx
> Geek#1113 (G-1)