Steve,
In my VTTC's I've reduced the number of turns on the feedback coil
if needed so that I could lower the feedback coil to a desirable
position. So yes, I'd say you are correct in your assumption.
John
-----Original Message-----
From: Steve White <steve.white1@xxxxxxxxx>
To: Tesla Coil List <tesla@xxxxxxxxxx>
Sent: Tue, Apr 3, 2018 9:38 pm
Subject: [TCML] VTTC grid feedback coil
Starting out with a 17" spark length, after a lot of adjusting and tweaking, I have finally achieved a 22" spark length on my 833A VTTC based on Steve Ward's reference schematic. I think there may be a bit more though.
My question concerns the grid feedback coil. I started out with 20 turns as per Steve Ward's schematic. Since my feedback coil was at the top of adjustment range of 3" above the primary coil and performed worse as I lowered the feedback coil, I reasoned that the grid feedback voltage was too high. So I have been gradually removing turns until I am now down to 16 turns. Each turn removed slightly increased the spark length but the feedback coil still needs to be at the top of its adjustment range for best spark length, so I assume that I need to remove more turns.
Am I correct in assuming that as I move the feedback coil closer to the primary coil, the feedback voltage increases? Does this imply that the number of turns in the feedback coil can be traded off against the distance (coupling) between the feedback coil and the primary coil? In other words, for the grid feedback coil, can I reduce the the number of turns in the grid feedback coil and then compensate for that by reducing the distance (increasing the coupling) between the feedback coil and the primary coil? My grid feedback resistor is set at 2500 ohms which seems to give the best performance.
I don't want to go too far with reducing turns. I could just rewind the feedback coil if I go too far but I would rather not.
Steve
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