Re: [TCML] VTTC-tuning. John got me started ;-)

[futuret@xxxxxxx]

Chistoph,

Generally speaking, if the spark length stops increasing at a
certain point as you turn up the variac, this means you need
to lower the tank frequency by increasing the tank C or
using more primary turns.  Probably best to use more primary
turns.

If you can get rid of the multiple streamers that will help
the spark length.  The multiple streamers could be the
cause of the shorter sparks, instead of what I said in the
paragraph above.  But regarding tuning, the primary tank
often has to be considerably lower in frequency than the
secondary frequency, from a calculated point of view.  This
takes care of spark loading effects, and frequency splitting
issues.  Tuning is best done at full power.  You can do this
by trial and error my moving the tap point on the primary
and turning up the power.

You can try using a taller break-out point, that might help
in getting a single streamer.  Tuning can be a factor there maybe,
and also the other fcators I mention above.

Various factors such as the degree of grid feedback, grid
resistance, tuning, main coupling, etc can affect the look
of the spark, and make them swordlike or fuzzy, etc.   It can
take awhile to really optimize a VTTC.

You can probably set the staccato board without a scope
by listening to the sound of the sparks.  When it's set up right,
the pulsing will sound "solid".

Is your main power transformer a powerful one?  That's important
also for tube coils.

Cheers,
John
-


-----Original Message-----
From: Christoph Bohr <cb@xxxxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Mon, 30 Mar 2009 3:55 pm
Subject: [TCML] VTTC-tuning. John got me started ;-)



Hello again.

As you might have followed, I was pretty happy with my VTTC's
output, until "someone" pointed out there was plenty of room for
optomization ;-) I'm just kidding...

One thing on the history of this project. During a first higher power 
run
of the prototype I had a sparkling effekt inside the tube, presumptively
at the cathode. I nedded a second to turn the power off and since then,
the fillament is notably brigher in this spot when switching the 
filament
supply on. With soft-start this is less visible and once the fimament 
is on,
I cant see any difference. However, the tube still lives, but I don't 
want to
break
it.
Currently there are 2 major question troubling me:

1:
One thing I noticed is, that when I increase the pulse rate or power, 
there
is a point at ca 70% from where on I get multiple streamers, pretty 
bushy and
white hot, but the lengts does not increase from this point on.
I sould be around calculated 250KHz, which seems to be problematic from 
what
I have read. Without toroid I could get to 330KHz... would this be 
worthwhile
trying?
Sounds dumb, but the toriod is glued to the secondary ( OK, even dumber 
)
I could of course detatch it, but I'd like to ask first if this makes 
any sense
at
all.
My idea was, that if there was a single streamer instead of multiple, 
it might
be
longer without having to push the tube any harder.

2.: I read I needed a scope to setup staccato. I just made a PCB, 
soldered
everything
together, plugged it in, and it worked... at least I think. I have a 
scope, but
no
idea
what I should set up what can't be done with the controlls available on 
the
fly...

3.: coupling. currently the bottom turn of L1 and L2 are aproximately 
on the
same
hight.
The feeback winding starts 1cm blow the primary and extends 15 turns 
until 4,5cm
below. Does this sound reasonable? I know, its impossible to give exact 
numbers
her,
I just want to see if someone says something is completely wrong....

Enough for now. For extensive tuning I should move over to my parents 
house.
I am living in an appartment which might be asking for trouble with my
neighbours
or the authorities.

best regards

Christoph Bohr


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