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Re: [TCML] Tuning Questions
Matt,
Thank you very much for replying to my questions.
This evening I added the "off axis tuning" inductor and beefed up all
the connections in the primary. As probably everybody else knows
chasing the optimum primary tuning is a bit like shooting at a moving
target because the secondary tuning changes when streamers or arcs
develop. Anyway, I didn't find much improvement here.
I tried a nice tidy "professional looking" nail break out point on the
top load toroid and it it doesn't work as well as the previous
screwdriver hanging over the edge of the toroid.
Then I had a Eureka moment. I raised the primary 1.5 inches and the
coil really woke up. I guess it needed tighter coupling. I need to
redesign the primary and try even more coupling. So, I have another
question for those more experienced coil builders. Is the need for
close coupling a common characteristic of an under powered coil such as
mine? If I parallel a second OBIT will the extra available driving
current lessen the need to tightly couple the primary and secondary?
Thanks
Charlie
K3YA
----Original Message-----
From: mddeming@xxxxxxx
To: tesla@xxxxxxxxxx
Sent: Sat, Feb 13, 2010 1:29 am
Subject: Re: [TCML] Tuning Questions
Hi Charlie,
That is not an unusual drop-off for a one-turn adjustment. Most of the
adjustable coils I've seen can be tuned to 1/6 or 1/8 turn; some finer.
IIRC,
yours is a helical primary so each turn contributes about 4 uH. Your
added
inductor will provide 2 uH , about 1/2 turn effective adjustment- still
a pretty
crude tuning step. Your added inductor will need to be fairly beefy to
not add
significant resistance or to short out between turns. You might want
to check
the archives for "off-axis tuning coils". This is why a majority of
coilers use
space-wound bare primaries to allow for easy optimal tuning.
Humidity does affect the maximum voltage that can be achieved prior to
breakout.
As a rough rule of thumb, 2 KV(rms)/mm is average for a static gap so
your
setting is good. (10 KV=>5 mm)
Matt D.
-----Original Message-----
From: cbroring@xxxxxxx
To: tesla@xxxxxxxxxx
Sent: Fri, Feb 12, 2010 10:26 pm
Subject: [TCML] Tuning Questions
This is my new and first coil that I posted about two weeks ago. To
recap the
specs are a 10kv 23mA OBIT, 3 segment spark gap with a fan, bucket
style salt
water capacitor around 12nF, 35uH 10 inch diameter 9 turn primary with
5 tuning
taps available. 1300 turn 3.5 inch diameter secondary and 18 inch
diameter
toroid top load. I'm getting about 12 inch sparks. The top load, spark
gap, and
primary capacitor are new since my first post
My first question is regarding tuning the primary coil. It seems to be
very
sensitive to tuning. One turn either side of optimum setting and the
streamer
length drops by half. Is this typical and does this have any
significance? I
don't have "half turn" taps available. Is there any reason not to add
in a
small, easily bypassed, 2uH, inductor in series with the primary coil
in order
to provide smaller tuning steps?
My second question, does humidity have a significant effect on streamer
length?
The garage where the coil is located has been seeing pretty dramatic
changes in
humidity (and temperature too). Can I disregard humidity in measuring
streamer
length?
I have one segment of my spark gap shorted out. With 4 segments, the
spark gap
gets significantly louder, but streamer length is unchanged. The total
spacing
or the current 3 segments is only about .180" (4.5mm). This is much
less then I
used with a single gap. Does this sound right?
Last question, if I leave the salt water capacitor in the unheated
garage will I
have a problem with salt precipitating out of solution when it gets
below
freezing?
By the way, over 3 feet of new snowfall over the past week in the
Washington DC
area!
Thanks for any help. I couldn't find the answers in the list archives.
Charlie
K3YA
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