"The Malcolm Test Results" was, 120 bps vs. 240 bps comparison tests

Test results below:

> Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> 
> Hi John,
>          Thank you kindly for agreeing to perform these expts: >snip
>  That might be so if the voltage is too low for the new ROC. Perhaps a 
> bump to keep minimum ROC constant might be useful.    >snip
>  Sounds exactly what the test needs. Many thanks again. I'm looking 
> forward to hearing the results.
> Regards,
> Malcolm  >>

Hi Malcolm, all,

I performed the tests suggested by Malcolm.  Here are the results:
(note: all tests done at 120bps)   Table at end of post.

Test 1.    Using a 3" by 10" smooth toroid with bump to create only 
one streamer, 0.0077uF cap, and 3.6 divisions on the o'scope, the
TC gave 17" sparks to a grounded measuring wire.  The spark hit the
wire occasionally.  Primary tapped at turn # 24

Test 2.    Toroid was replaced with a 6" by 26" dryer duct toroid with
bump, 0.0077uF cap, and 5 divisions on the scope, for a doubling of
the bang size by using 41% more cap voltage.  The spark length 
increased to 22" for a 30% increase.  Sparks were a little thicker and
fuller probably.  (tapped at turn # 33)

Test 3.    For  added insights, I went back to the 3" by 10" toroid, but
used an input voltage of 5 divisions on the scope, this gave multiple
streamers and a 26" spark.  

Test 4.    Finally, as a sort of cross-check, I went back to the 6" by
26" toroid, but used a 0.0147uF cap, with voltage of 3.6 divisions on
the scope, for the same bang size as test 2.  This also gave a 22"
spark, but maybe slightly stronger.  This may be because the 
pri tap is brought back to turn # 25 from turn # 33 in test 2.  (Probably
tighter coupling than in test 2.)  The fact that the tank cap size is 
approx double, and the pri tunes at about the same tap point with
this large toroid as with the small toroid and small cap, suggests
that Cs + Ctop total has approximately doubled with the large toroid.

Conclusion:  These tests suggest that doubling the bang size while
keeping Vo constant gives about a 30% spark length increase due 
to the extra topload current.

It is interesting to note that the spark increases about 50% from test
1 to test 3, which is more than I would have expected.  I expected a
40% gain or less.  It is possible that the coil is not at a sweet spot
in test 1, which might invalidate the results and conclusion to a 
degree?  For instance if we assume that the TC "should" give an
18.5" spark in test one, then the gain in test 2 would be about 20%
rather than 30%, a decrease, but it wouldn't change things much in
the overall scheme of things.

I'm just listing scope divisions rather than voltages in case the scope
is reading incorrectly, but I believe it IS linear, so relative measurements
of this sort should be accurate.  Note that in the last test I seem to have
the sync gap phase set more efficiently, but it doesn't matter, I went by
cap energy at firing, not input watts.

BPS  Div    meter W   toroid     Cp(uF)     spark 
120    3.6      220          10"    .0077          17"
120    5.0      440          26     .0077          22   (30% increase)
120    5.0      430          10      .0077         26  (mult. streamers)
120    3.6      320          26      .0147         22

Comments welcomed,

John Freau