Re: [TCML] Tuning Questions

[mddeming@xxxxxxx]

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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