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Re: Regulating coil: here's a big one!

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Scott,

On 27 May 2002, at 7:52, Tesla list wrote:

> Original poster: "Scott Hanson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <huil888-at-surfside-dot-net>
> In an attempt to help put an end to the "variable capacitance" debacle, I
> thought I'd add a bit to the "regulating coil" thread.
> Saturday I picked up the largest variable inductor I've ever seen at the TRW
> electronics swap meet in So Cal. Unlike the commonly seen ex-military roller
> inductors, this one is "really big", and utilizes utilizes a pair of solid
> copper "shoes" on a slider to make contact with the windings. The
windings are
> rectangular section solid copper, .185" thick X .325" wide. The coil is
6" long
> X 6.5" in diameter, with 14 turns total. As measured using a Sencore Z-meter
> II, the range of inductance adjustment is from .1uH to 20uH. Weight is just
> under 20 lbs.
> Some photos of this inductor can be seen via the following links. The
files are
> 150 - 200 kb in size, so they may take a little time to load.
> <http://surfboard.surfside-dot-net/huil888/variableinductor1.jpg>http://surfboa
> rd.surfside-dot-net/huil888/variableinductor1.jpg
> http://surfboard.surfside-dot-net/huil888/slider.jpg
> <http://surfboard.surfside-dot-net/huil888/coronaburn.jpg>http://surfboard.surf
> side-dot-net/huil888/coronaburn.jpg
> http://surfboard.surfside-dot-net/huil888/variableinductor2.jpg
> Technically, using a regulating coil "wastes" some of the energy in the
> circuit as its magnetic field is not coupled into the secondary. However,
> loss might be offset by the ability to fine-tune the primary circuit's
> frequency as the coil is actually operating.

If the coil and its core are lossless, it will waste no energy at 
all. It *will* reduce pri-sec coupling as more inductance is added 
in. If the coil is air-cored, wound with large diameter copper and 
the inductance adjusted by winding compression, losses should be very 
low indeed.

> The photos show several views of this massive inductor. An interesting
> is shown in the photo labeled "corona burn". Clearly visible burned into
one of
> the insulating end plates is a flame-like defect originating at a sharp
> of the square slider-shaft. The distance from this corner to the brush plate
> (opposite terminal of the coil) is slightly over 2". It appears that this
> was operated for some extended period of time with considerable corona
> originating from this point.
> As soon as I can rig up a gear motor to allow this to be adjusted from a
> distance, I'll add it to my 6" X 32", 120ma NST-powered coil and see if
> tuning is worth the effort.
> Scott