Re: Magnifier coupling measurements, new (update) (fwd)

---------- Forwarded message ----------
Date: Fri, 10 Jul 1998 14:31:30 EDT
From: FutureT-at-aol-dot-com
To: tesla-at-pupman-dot-com
Subject: Re: Magnifier coupling measurements, new (update)

Hi Malcolm, all,

Thanks Malcolm,  your suggestion was exactly correct.  I remember 
when you said you had to look for the sweet spot for the probe.  I did 
this and now my waveforms are clear, and I see normal energy 
transfers in all cases, and the results are close to what I had seen in
previous work a few months ago.  More findings and comments below:
> ---------- Forwarded message ----------
> Date: Fri, 10 Jul 1998 09:36:05 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Magnifier coupling measurements, new (fwd)
> Hi John,
>            Thanks for the further measurements of magnifier k's. I 
> have two comments:  Firstly, the overall k of my system was almost an 
> order of magnitude below the driver itself because the driver 
> secondary had such a small fraction of total secondary inductance. 
> Driver Ls was about 350uH and resonator around 7mH if memory serves 
> me sufficiently.

Yes, I was able to simulate these very loose k's only by the use of the
variable secondary tune capacitor.  In my latest tests, I was also able
to use the var sec tune cap to make the k tighter, for 1st RF notch at
3uS corresponding to  k (actual) of 0.33, (driver k = .4).  This agrees
with my work from a few months ago.  Without the variable tune cap, 
I can see that the actual k = 0.2, again similar to what I had seen a few 
months ago.  More below.
> > ---------- Forwarded message ----------
> > Date: Tue, 7 Jul 1998 09:10:48 EDT
> > From: FutureT-at-aol-dot-com
> > To: tesla-at-pupman-dot-com
> > Subject: Magnifier coupling measurements, new
> > 
> > All,
> > 
> > In these tests, I looked at the primary current waveform by using
> > a current transformer attached to an oscilloscope.  These tests
> > provide further verification that despite the tight coupling of a 
> > magnifier driver, the overall coupling of a magnifier is loose, and is 
> > typically within the range of two-coil Tesla coils.  (In my previous
> > tests, I looked at the secondary or extra coil waveforms.)
> > 
> > I used the same old set up with pri, 19 turns, # 12 wire, sec, 1.5mH
> > 6.5" dia by 3.4" high, # 24 pvc, driver k = .4, extra coil = 11.4 (13?)mH.
> > 3" by 12" # 28 formvar, tank cap = 0.0015uF, Fo = ~500kHz, toroid is
> > 1.5" by 4.5", synch gap 8 point series quench type, (4 points used),
> > powered by 10kV, 23ma oil burner ignition transformer.  A variable tune
> > cap (34pF to 167pF range) is installed across the secondary.
> <snip> 
> > Figuring the effective or actual coupling based on a 28uS beat, gives
>> > k = 0.07 which is quite a low figure.  But it compares well with
 > results where his 0.54 driver k fell to k = 0.086 actual overall system k.

Malcolm, I agree that your loose k resulted from the large sec/extra coil
L ratio.  My k without the tune cap is 0.2 due to the smaller L ratio in my
system.  I'm still seeing the 28uS beat (k = .07) when I adjust the sec
var tune cap a certain way.  I think I get a good spark with this adjustment
because it reduces the number of energy transfers, and therefore the 
losses, (but I don't trust this result, spark is long, but total energy in
the toroid seems low).  Now if I could quench (properly) at the other 
tune cap adjustment that gives the 3uS 1st notch...that would be 
interesting, and the spark would probably be stronger.  Especially 
since the secondary energy peak is stronger when adjusted for a 3uS
transfer, than when adjusted for a 14uS transfer (less gap loss due
to fast transfer).  When I change the sec tune cap adjustment from
short 3uS beats to long 14uS beats, the scope RF amplitude drops
from 3 divisions to 1.5 divisions, (probe is not calibrated).

As a final test, I configured the sec var tune cap to give a greater
capacitance range (but lowered voltage capability).  Now an even
longer beat could be produced, such that the 1st RF notch occured
at 24uS, and the quench occured at that point.  This gives a k of
0.04, and the spark output is killed.  This is probably because so
much energy is lost in the gap during the long transfer, that not
enough winds up in the secondary to cause breakout.

In summary, now that I'm seeing the waveforms better, I can see that
some k's are a little tighter than mentioned in my last post, but are
still much looser than the driver k when I'm not using the tune cap.
For instance actual k = 0.2 with driver k = 0.4.  But when the sec var
tune cap is installed, the k can be made much tighter, for instance
k = 0.33, (or looser at actual k = .04), with driver k = 0.4 in all cases.

The sparks were somewhat strong without the var tune cap, and
were somewhat strong with the var tune cap adjusted in certain ways,
but the results are bollixed by the poor gap quenching capabilities.

I don't think I can go any further with these tests without being able
to quench better.  Of course if we could quench better, imagine what
could be done with classic TC's.  (We'd actually get that 4% longer
spark   :-))

Thanks again,
John Freau

> Thanks for an exceedingly interesting post.
> Regaards,
> Malcolm