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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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