Re: [TCML] Tube question

[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 <drieben@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
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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