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Re: [TCML] 810 tube coil

Thanks Chris/All - Very interesting thought about the level shifter. I've wondered if it is really necessary in this particular circuit. (I couldn't see your PDF) A lot has happened since my last posting, I was going to report back next week with a new vid. It was time to do some serious research and experimenting on my own. I found I have a few Radio Engineering books from the early 1900's one of which is "Radio Engineering" by Fredrick Terman, this book is wealth information on Amstrong Oscillators and there design, tuning and operation. Many of my questions were answered. First, I was surprised that our VTTC circuit was one of the first tube transmitting circuits, developed just a few short years after Tesla did his thing back in 1899, second the grid coil is used to provide feedback from the PRIMARY coil 90 degrees delayed from the primary, third even with these early experts final tuning was a trial and error task. These old Radio books are worth there weight in gold for our Tesla coil Passion! Knowing that the grid coil couples with the primary only, answered one of my burning question. It does not matter if the grid coil is above or below the primary coil and winding direction does not matter but the polarity of connection into the circuit matters (you only get two choices). The Secondary is separate and does not matter which way it's wound. Trial and error tuning is the only way to get on the air. Now for my coil. I moved the grid coil below the primary to get away from the secondary. I wound a primary with taps every turn and experimented with primary tuning and found that the 36 turns that I was using was way to many, it turned out that ~26 turns seemed to be the sweet spot (I think my building guidance had a typo :) ). Next I was able to win a bid for a Jennings Variable Vacuum Capacitor, 10kv @1.2nF, at a very reasonable price. This allowed me to fine tune wile the coil was running! and quickly saw the point of max out put and minimum plat current, getting better all the time! Next I found a NOS JAN 810 and replaced the tube. Wow that was another problem, my original tube was weak, this new tube is a lot more powerful and can handle a lot more current without getting red! I'm not done fine tuning but already It's up to 12" of spark!
Next week I hope to finish fine tuning and post a vid.


On 1/13/2018 9:32 PM, Chris Reeland wrote:
Hi Dave,

I am pretty positive I have figured out your poor performing coil.

You need to remove the microwave caps and the microwave diode from the MOT.
You need to take the Level Shifter off and run just the AC from the MOT.

And then tune in the coil for this of course...

Let me explain...

A few days ago I did an experiment on a very recently rebuilt coil, built
originally 30+ years ago. Never really worked at all after several tries by
my Dad and me. So I decided to dust it off and try again. Changed a lot of
things, not going into all details...but it is basically an old school very
tall skinny "candle stick" coil. Changed to 2 old 811 tubes with a MOT
using AC normally. And all Mica Caps. (Just a note, these tubes are 811's,
not 811A's. They are somewhat rare precursors. It is what I had on hand.
They are a little different.) Got it tunned up and running pretty good.
10.5" arcs. I'm very happy for a candle stick.

So I started to think about your 810 coil again. Realized finally that you
said your running a Level Shifter, but not Pulsing coil yet. This is the
problem. I watched your 2 videos again to verify. I do Pulse another coil
with LS.

I have never run a coil LS alone, so I decided to try on this coil with no
other changes at all.

VERY POOR. Milliamps climbed extremely fast as I was turning up the variac.
Got to max Ma. for 2- 811's very quickly with way less voltage than before.
Just 3-4" arcs now!!! Ran just like yours in the video!!! Everything
getting hot also!!! Could not run very long!!!

Thought about this some and realized why.

I'm going to put links of several pictures and a video.

Going to link a PDF also of a paper I drew up to explain what is going on,
with a few other thoughts also on it.

Picture of coil.


Running good picture and video.



Running poor picture.


PDF explaining why.



Some thoughts and/or corrections are welcome if I am wrong on any thoughts
on this.

Sent from my LG V20
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