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Re: [TCML] Method for attaining CW in VTTC

Hi Chris,

I tried 2 other 833A tubes today just to eliminate that as a possibility. There was no difference in performance so my original NOS Amperex tube is good.

I also experimented with the grid feedback today. I suspect that my grid feedback voltage may still be too high. When I moved the grid feedback coil 1/2 inch higher, the spark length increased by about 1/2 inch. This places my grid feedback coil 3 inches above the top of the primary coil. I am now at the top of the range in height that I can move the feedback coil so I am considering removing some more turns. I started with 20 turns as per Steve Ward's schematic. I eventually removed 2 turns right after I completed the coil to get down to 18 turns so that I could move the feedback coil lower (closer to the primary). I also played around with the grid feedback resistor. 2500 ohms seems to give the best performance.

As you requested here are the differences between my VTTC and Steve Ward's design:

* Primary coil: 27 turns, 8 gauge, 6.5 inches winding height, tapped at turn #25 from top
* Grid feedback coil: 18 turns, 22 gauge, lowest turn of feedback coil is 3 inches above top turn of primary coil
* Grid feedback resistor: 2500 ohms

The spark from the secondary trying to reach the grid feedback coil is very rare. I have only seen it happen twice. When it does happen, it is where one of the feedback coil mounting terminals is at its closest to the secondary coil. This is about 2/3 of the way up the secondary coil.

In CW mode, the VTTC pulls about 19 amps. In pulse mode, it pulls about 16 amps as close as I can read.


----- Original Message -----
From: "Chris Reeland" <chrisreeland@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, March 29, 2018 6:55:12 PM
Subject: Re: [TCML] Method for attaining CW in VTTC

Hi Steve,

I can't say for sure, but I'm starting to wonder about something not being
right with the feedback winding, which is causing the limited current. If I
remember correctly, your grid leak cap and resistor values your using
should normally let quite a bit of current to pass.

Also when you say the arcs/shorts from the secondary hitting or trying to
hit the feedback winding, where are they specifically coming from? From the
bottom of the toroid? From the secondary winding itself? If winding, what
height? From below a bit, straight across, or from a bit upward?

Wish I could see what you have going on there or even be there to try to
figure out what is going on.

I know you have said you feel the tube is good and strong, so I am leaning
towards the feedback winding. A bit bothered that your still having
possible strike issues even with the guard ring in place.

Me, I'm peaking at 17 amps now. Went up 1 amp. This is with the PFC caps in
place. So, I would say without PFC from what I was seeing before the
circuit breaker tripping problems previously about 24+ amps on the 120v
line. Definitely tripping of course...

So I am definitely able to conduct "heavy". My tube during the peak of the
pulse rate that I am currently at, is just getting slightly orange spots
pulsing of course. So my tube is not working too hard.

Could you give some dimensions of all three windings and wire heights that
they are located at? All wire guages and turns, think you said #8 primary,
feedback about 2" above.  I forgot the rest. Tried looking at some past
messages, can't find it yet on the specs. I know it is based off of Ward's,
but some changes.
You have some height adjustment possible of secondary also I think, don't
remember how much.

Trying to get some ideas...


Sent from my LG V20
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