Re: Advice on secondary

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Steve,

On 31 Jan 2005, at 7:16, Tesla list wrote:

> Original poster: Steve Ward <steve.ward@xxxxxxxxx>
>
> Malcolm
>
> How did you determine the Q of your coil?  Was this measured?  Im just
> curious if you had a nice process for accurately measuring it (since i
> dont know how to take form material into account in theory).

It was measured. The coil was isolated as far as was possible from
the floor, ceiling walls and other fixtures in a classroom here and
base fed from a very low impedance (<1 Ohm) source.

Aside: That source BTW is current limited to several Amps and has a
visual indicator to indicate when the limiting kicks in (which is
when the output impedance deviates from ideal). It has never limited
base-feeding a resonator but easily does so when pumping a resonator
via a primary coil - endaside.

 The electric field was monitored by a probe suspended over six feet
away from the coil and the readings taken on an oscilloscope.
Interestingly I detected (I forget the exact figures but do have them
recorded somewhere) a drop in Q from something like 320 on a very dry
day to about 300 the next day when the humidity had climbed well
above 50%. Needless to say, a number of readings were taken and
averaged to arrive at the final figures with re-reading and checking
for repeatability, errors etc. being standard. There were no readings
that could be regarded as outliers (the readings concurred within a
1% range).

> Just a side comment about cardboard forms.  I used a sono-tube form
> for my big DRSSTC.  I removed the outer layer of paper with the
> writing on it and put 2 coats of varnish on it.  Sanded it then wound
> the coil.  Its 8"x45" and has produced nearly 12' sparks so far.  Im
> very curious to find out the Q of this coil though, as the idea of the
> cardboard form still worries me a bit.
>
> Steve W

It sounds as though you didn't dry yours either but you may have had
the good fortune to have done it during a run of several dry days.
>From a coil winder's point of view, it seems easier to just use PVC
or some other plastic rather than having to go through the rigmarole
of organizing an elaborate drying setup. I've never bothered
preparing coil forms other than a quick wipe with meths to remove
dust and stains and that particular cardboard one was the only real
failure I've had. Small coils I've wound on cardboard inners from
handtowel rolls and the like were never as bad.

Malcolm



>  > I have a spacewound secondary wound on some thickwall sewer pipe >
>  (no previous sealing or other treatment) which has a Q in excess of >
>  300 at 165kHz. With Q's that high, differences in dielectric >
>  dissipation are a non-issue. The only secondary I wound which came a
>  > cropper was wound on some sonotube-type stuff with the tar paper >
>  removed. It was largish, spacewound and its Q barely clocked in >
>  around 40 with powered results to match. It was varnished but I >
>  didn't bother to dry the stuff prior to coating. My fault of course.
>  > > Malcolm > >
>
>
>