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Re: 1/4 wave TC (fwd)

---------- Forwarded message ----------
Date: Wed, 25 Jul 2007 00:37:47 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: 1/4 wave TC (fwd)

Hi Skip,

Can't comment too much on your specs as there is info not listed that 
makes a difference. I'm assuming from the primary spec in relation to 
the secondary size that the primary is helical. If true and there's also 
1/4" edge to edge spacing with the 1/4" tubing, then your looking at a 
primary resonance at 171 kHz. If flat, about 206 kHz with your cap size. 
But that would be odd because the 19" diameter would indicate a 9" inner 
diameter with the secondary at 14". That type of coil would need to be 
placed below the secondary. Thus, I assumed helical.

I noted a 55 kHz change between a double stack toroid and a single 
toroid. That's a huge change in frequency! I can only assume the toroids 
are separated by a good distance? Either that or I have to really 
question the accuracy of the measurements.

The cap size is causing resonance of the NST on the low end. It's 
slightly out on the low end but still receiving a good deal of resonant 
charging. Thus, the voltage is likely far higher than 9kV output at the 
cap at the time of discharge and this explains the safety gap firing. 
Unlike some of the others that responded, I would not open the gap up 
further. The gap is actually self limiting the voltage and has prevented 
the NST from death. If you open the gap up, you'll allow a higher charge 
at the cap which "will" be felt back on the hv coils of the NST. If high 
enough, it will overvolt them. The only solution here I would do is to 
increase the cap value between .05uF and .09uF.

To obtain a single spark channel, the double toroid is not the way to go 
(the stack you show has the same radius of curvature). You'll need a 
smooth toroid which is larger in size. A size of 9 x 30 might obtain 
that condition.

Take care,

Tesla list wrote:

>---------- Forwarded message ----------
>Date: Wed, 25 Jul 2007 12:21:32 -0400
>From: Skip Greiner <skipg@xxxxxxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: 1/4 wave TC
>Hi All
>Well after my capacitor literally exploded and destroyed both the 
>primary and secondary of the first 1/4 wave TC, a new one has been built 
>and is in test. The specs are:
>Primary: 7 turns, 1/4" tubing, 19" in diameter
>Secondary: 390 turns #22ga, 0.050" overall diameter insulated wire, 14" 
>diameter, winding len:19.5", frequency len of wire: 217khz, wire length 
>Measured Resonance of secondary is 210 khz. no excitation
>With 5 x 20 toroid: 205khz
>With two 5 x 20 toroid: 150 khz
>Driver: 9kv x 120ma NST
>Break: SRSG with 2 poles
>Cap: .027
>Some of the test results:
>Variac set no higher than 40 or about 50 volts input
>Spark length:
>No toroid: multiple 12" (+) arcs from top turn of sec
>One toroid: 20" (+) from breakout point
>Two toroid: 27" (+) from breakout point
>Operating freq: with toroids: 140khz
>Operating freq: without toroids: 190khz
>Note that the wire length frequency and the operating frequency with no 
>top load under power are pretty close. I am trying to figure out how to 
>concentrate the discharges into a single streamer without a top load. I 
>seem to be processing a large amount of power and the total amount of 
>sparks with or without a top load seems to be similar.
>Above the "40" setting of the variac the NST safety gaps really fire 
>nearly all of the time and so far I am afraid to open up the gaps which 
>are set to about 0.125". Does anyone have a comment as to the maximum 
>safety gap opening that I might use on a 9kv NST? It looks like this 
>thing will really perform at higher inputs but I do not want to risk the 
>NST yet.