Please Help! Trying to tune the primary coil (fwd)

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---------- Forwarded message ----------
Date: Sun, 24 Dec 2006 20:34:19 +0800
From: westland <westland@xxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Please Help!  Trying to tune the primary coil

Hi All:

I've gotten to the stage where I need to tune my primary tap point, and 
I've run into a problem in trying to figure out how to wire up the 
primary coil to find the resonant frequency.    I initially pulled the 
secondary, put it on a plastic base, injected RF from my signal 
generator, and read the response off of my oscilloscope with a small 
antenna set as the input feed.  This worked well, and gave me a resonant 
frequency of 205KHz for a 4" x 22" coil with a 5x16 toroid topload.  
Here are pictures of the setup (sorry for the fuzzy initial picture)

Secondary tuning setup Antenna:    http://www.flickr.com/photos/51115445@N00/331719458/

Secondary base (so it doesn't fall over when measuring):  http://www.flickr.com/photos/51115445@N00/331719464/

Secondary tuning setup:  
http://www.flickr.com/photos/51115445@N00/331719457/

********

So far so good.  So I hooked up the primary and the MMC (which I had 
tapped for 10.2 nF... see pic).  But I couldn't figure out how to wire 
up the tank circuit so that I could get a reading off my oscilloscope of 
the response to the injected RF signal (I tried several configurations, 
plumbing the Internet for sources, but couldn't get anything to work ... 
my voltage rises were all in the over 1 MHz area).

I decided to compute from readings off my RLC meter, and found that I 
needed to tap near the end of my 14th winding (with the 10.2 nF cap) to 
get a resonance of 205K.  But even with this setup, I couldn't get the 
scope to give me any readings at all in the low kilohertz rang.  Here 
are more pictures of the setup.  I also tried to test the complete coil, 
but that didn't work either.

Measuring impedance of MMC:  http://www.flickr.com/photos/51115445@N00/331719460/

Trying to measure resonance of primary coil:  http://www.flickr.com/photos/51115445@N00/331719462/

Measurements for complete Tesla coil:  http://www.flickr.com/photos/51115445@N00/331719463/



Can anyone give me advice on where I am making my mistakes here.  From the descriptions I've read on the Internet, tuning the primary should be straightforward (but no one tells you how to wire up the test setup).  You are looking for two peaks with a valley at the secondary resonance (indicating the secondary is drawing power away from the primary circuit)

Thanks in advance for the help

Chris Westland











-- 
____________________________________________________

J. Christopher Westland, PhD CPA
Professor, ISMT, University of Science & Technology, HK Clearwater Bay,Kowloon, Hong Kong
Tel: 852 2358 7643
Fax: 852 2358 2421
Mob: 852 9528 1745
URL: ihome.ust.hk/~westland
Mobile e-mail: chris.westland@xxxxxxxxxxxx