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R: 813 in my vttc...
Original poster: "Vladimiro Mazzilli" <V.Mazzilli@xxxxxxx>
Hi Brett,
With which power supply are you running? Mot? Doubled? With shunt or not?
In my experience I prefer to polarize G2 and bypass it with a capacitor.
Especially in little power tube, to avoid destructive flashover.
Vladimiro Mazzilli
Ricerca & Sviluppo
Aros Srl
Via Somalia 20
20032 Cormano (MI)
Tel. +39 02 66327266 - Fax. +39 02 66327528
email: V.Mazzilli@xxxxxxx
Web: http://www.aros.it
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-----Messaggio originale-----
Da: Tesla list [mailto:tesla@xxxxxxxxxx]
Inviato: lunedì 12 febbraio 2007 5.08
A: tesla@xxxxxxxxxx
Oggetto: 813 in my vttc...
Original poster: Brett Miller <brmtesla2@xxxxxxxxx>
All,
I have gotten satisfactory sparks from placing a
single 813 in place of the 833A in my vttc system.
They are not as long as the 833A sparks, but they look
good and the system draws much less power from the
wall in this configuration. Plus, the graphite plate
runs pitch black until about 130v is reached on the
variac. At full voltage (140v) it gets a cool dark
cherry on the plate, and the amp clamp shows no higher
than 14a. This is significant when you consider that
in the same system with the 833A plugged in, the meter
hit 21a peaks at the 140v setting, while making sparks
which were only about 5-6" longer on the avearage. I
haven't even tried optimizing grid leak resistance
yet, not to mention winding a new feedback coil.
The tube is running as a triode with G1 and G2 in
parallel, and G3 connected to ground through a jumper
to one side of the filament (cathode) connection on
the socket.
Here is the video...which is even pretty impressive in
daylight:
http://www.hot-streamer.com/brett/vttc/14inch813.avi
It's a bit over 8 megs in size...but not compressed
(at least not beyond what my cannon powershot does
already). After the voltage reaches 130v or so the
sparks average about a foot each easily, with sword
streamers exceeding this by a few inches now and then,
however, they diminish when the Yish caps heat up.
This test has shown me that even though the plate is
running cool, the tank cap (2 yish 1.1nf in parallel)
gets quite warm to the touch after even a 45 - 60
second run. This is a major loss point for my vttc
since I have found that the longest sparks occur
during the first 20 seconds or so on the first run
after the Yish caps are cooled off. Then performance
drops off by 2 or 3 inches subtracted from the spark
output.
The Yish doorknobs are inexpensive, great for filter
(and grid leak) caps, and they will work fine if you
are just hungry to get started on your 1st vttc. But
they are no substitute for higher quality caps that
will stay cool. Luckily, I have a big mica on the
way.
Working with the 813 is a lot of fun. It would not
have gone so well if it weren't for the personal help
I received from John Freau on this 813 project.
Thanks John! Also, the project would not have been
possible if it weren't for Dan Williams, who gave me
two new 813's. Thank you Dan.
Cheers,
Brett
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