Re: new single 833A VTTC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: FutureT-at-aol-dot-com 

In a message dated 12/24/03 1:05:56 AM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

>Also, i know its hard to explain with words, but how red is
>'acceptable redness' ?  I have been letting the plate of my tube just
>noticably get a pinkish glow to it in the center of the plate.


Steve,

The 833A tube specs indicate that the plate will run red/orange
at full power rating.  It's not so much the brightness of the plate,
but rather the color that tells the temperature.  Of course when
the plate is hot like this, it's more susceptible to HV arc-overs.
If the tube is cool it may be able to be run at 6kVAC, but if it's
red/orange it may only withstand 5kVAC.  The tube is rated for
4kVAC, I know you know this but I have to mention it or others
will write to tell me.

>Also, do your notes mention the parameters of your setup? mainly the tank
>cap as well as the level shifter capacitor?


The tank cap value only has significance when considered along
with the inductance.  This was basically my large coil which I believe
is shown at David Trimmell's website.  It's the one that shows two
tubes and gives 33" sparks using staccato I think.  In the tests I
mentioned, I used just one tube and no staccato.  Some of the
values are changed from the schematic and are shown below.
I used two level shift caps for a total value of about 1.8uF or so.
Things were rather critical, for example if I used 0.006uF for the
tank and retuned, I lost 1" of spark length compared to the results
using the values shown below.

Coil specs:
Tank Cap value =  0.005uF
Primary turns = 30 (15 degree flattish primary, 12awg pvc ins.)
Variac setting = 131 volts
Secondary coil is 6.5" diameter polyethylene form wound 22.5"
using #28 formvar magnet wire.  The bottom of the secondary
is level with the bottom of the primary.  Secondary inductance
is about 95uH.  A steel flat cover 10" dia. is used and an anti-
corona shield topload.  It was the top cover from a can of Danish
butter cookies ( ho ho ).
The grid coil is 19 turns of 18awg pvc insulated wire wound on
a 8" x 1.25" form (two winding layers, 10 turns and 9 turns).
Grid resistor = 10k ohms in these single-tube tests.
Transformer = 2300V MOT with level shifter.
No staccato, acceptable tube redness.
Spark length = 22"

It think the small VTTC gave 21" sparks using (1) 833A with
the level shifted MOT and no staccato.  I'd have to check my
notes to be sure.  I took a quick look and couldn't find the info.
I always use a 6" toroid on the small coil because it adds
1" of spark length.



>respectively.  Oh, and how long could you run at 22" and
>non-staccato?


As far as plate-redness, it could run indefinitely.  It's possible
the tube-pin seals would eventually fail, and also the coil
windings themselves got kind of hot.

Just so i have something to go by.  Im sure i could push it

>for about 2 seconds before full redness sets in, but i have a feeling you
>were able to run it for awhile at that power.


Regarding destruction of 833A tubes, I used to arc them often
while I was determining their limits.   This was before I began
using the protective plate lead chokes so the damage was
extreme.  One time the grid wires burnt in two, and another time
the coating was blasted off the plate.  In one case the filament
shorted and was destroyed.  One tube became mirrored inside.
Once the tubes arced like this, they were more susceptible to
further arcing.  I think I destroyed two 833A tubes during this
early work.  Basically if the tubes are red, they can withstand
only 5kVAC.  If they are not red, they may withstand 6kVAC.
I used to supply about 7kVAC to the original (3) 833A coil which
gave 36" sparks.

Someone on the list asked why tubes other than the 833A are not
used.  833A tubes are used because they are somewhat robust
and can tolerate high voltages, and are somewhat readily available
at reasonable cost.  833C tubes can handle almost
double the power of an 833A it seems.  When I built my dual 833A
staccato coil which gave 24" sparks without staccato, I also
tested the coil using a single 833C tube.  This also gave 24"
sparks, but the sparks were not as nice looking, so I went
with the (2) 833A tubes.

Holiday Cheers,
John



>Steve
>
>
> >Steve,
> >
> >Nice results.  I'm reading my old notes from 2/20/98.  At that time
> >I installed a level shifted MOT onto my large VTTC while using a
> >single 833A tube.  This arrangement gave 22" sparks without
> >staccato, and the tube ran with acceptable redness.  The coil
> >drew 15A  at 120 volts.
> >
> >Just previous to my work, Rob Stevens of Canada built a magnifier
> >VTTC using a single 833A and level shifted MOT.  His setup also
> >drew 15A at 120 volts, and gave the same 22" spark length.  It
> >was not a staccato coil.
> >
> >Holiday Cheers,
> >John
>
>_
>