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Re: [TCML] Tube question
Ed,
I am not currently metering the grid (or plate) current
in my setup, so I cannot answer the current question. I
am really pretty dumb on vacuum tube coils and this one
was based loosely on Steve Ward's 833A VTTC that
is supposed to yield 22" sparks in stacatto mode. The
only difference is that I am using 2 seriesed MOTs
through the voltage doubler circuit, just like Cameron
Prince did on his. As a matter of fact it was my perso-
nal viewing of Cameron's coil's output that convinced
me to take on this as my first VTTC project. Anyway,
I have used two or three different used 833As and always
got about the same output. However, I decided to or-
der a new (Taylor) 833C because Cameron had pur-
chased a used one on eBay and had reported good
results, mainly the plate stays cooler at a given power
level. However, when I tried my new 833C tube in
my circuit, it had a very limited spark length output and
the spark output would not increase beyond about 40%
on the variac knob but would instead start to take on
a "crackly" sound. BTW, the output at this point is only
about a pitiful 6 to 8", in continuous mode! Further ramp-
ing up of the variac beyond this point does not increase the
spark length any further but it is apparent that there is more
plate current as the graphite plate will begin to take on a
glow. BTW, the output sparks will continue to grow pretty
well linearly with increase in the input via twisting up the
variac knob when using the old 833A until I can't really
turn it up much past 60% on the variac knob due to ex-
cessive plate glow (in continous mode), but the spark length
at this point is around 16 to 20". Any more suggestions, I'm
all ears :^)
--
David Rieben
-------------- Original message --------------
From: Ed Phillips <evp@xxxxxxxxxxx>
> You've never mentioned how much grid current you're running and that
> might give you a clue to whether you have enough grid drive with the newer tube.
> [Never have mentioned plate current either and both are of importance.] As for
> emission, boosting the filament voltage a volt might result in big improvements
> without reducing life to the point where you'd notice it, considering how many
> hours you're likely to run the setup. The fact that the carbon anode wasn't
> showing more than a "dull glow" suggests you could use more grid drive. What
> size grid resistor are you using?
>
> Ed
>
> "Hi David,
>
> I don't have much experience with the 833C. I did try replacing
> the 833A's in my 24" spark VTTC using the 833C's, and the
> spark was the same length. I also experimented using one
> 833C in place of the two 833A's and the spark was still the
> same length (maybe 1" shorter). I didn't make any changes
> to the circuit.
>
> I remember Tony DeAngelis telling me that he bought a
> new 833C tube and got only 16" sparks. Then he bought
> another 833C tube of a different brand and got 22" sparks.
> He's not sure if the first tube was defective, or had
> different characteristics, etc.
>
> I don't know if the breaking in of the tube will actually
> help the spark length. I thought the breaking in was
> to help absorb any left over gas in the tube before
> applying peak power and voltages.
>
> John
> ---
>
>
> -----Original Message-----
> From: David Rieben
> To: Tesla list
> Sent: Fri, 19 Sep 2008 9:51 pm
> Subject: [TCML] Tube question
>
>
>
> Hi all,
>
> I finally finished rewinding my VTTC secondary winding that I
> flashed over and ruined last week as the new spool of wire ar-
> rived today. I got the coil back up and running in continuous
> mode with no problems with my old original 833A tube. I'm
> hoping to get my stacatto controller fixed in the near future
> so I can get it to hurling those huge 35"+ flaming swords in
> stac. mode again. However, one issue that I am still having is
> that I justrecently purchased a brand new 833C tube from RF
> Parts to replace (or as a spare for) my old 833A tube. When I
> removed the 833A tube and replaced it with the new 833C,
> the output would only increase up to about 40% on the variac
> dial and then the sparks would start sounding "snappy" but
> would not get any longer with a further twist on the variac
> knob upwards. The tube plate was definitely processing current
> though as even the graphite plate began to take on a dull glow.
> The output would not get any better though and I had to re-
> install the 833A to get back a nice linear increase in output
> with an upwrad twist of the variac knob.
>
> Anyone know why I am experiencing this? The only thing that
> I can think of is that the manufacturer says smething about
> a "break-in" time before you start using them to there fullest
> rating. Could I need to run it for a while at low power to "break
> it in" to get it to function properly at higher power levels? It almost
> seemed like the coil was badly out of tune with the 833C in place
> while it returned to normal operation with the replacement of the
> older 833A. It is my understanding that the only difference between
> an 833A and an 833C is that the 833C has a more durable graphite
> plate. This is correct, isn't it?
>
> Thanks,
>
> David"
>
>
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