Re: [TCML] Choice of tubes for first VTTC?

[futuret@xxxxxxx]

Grant,

The 813's are nice tubes.  I did some quick tests in a VTTC and obtained
16" to 19" sparks from a single 813.  I applied about 4000 volts raw AC 
to
the tank circuit.  The 813's are much much more robust than 811A's.
The 811A tubes are rather wimply.  Their plates will get red at the drop
of a hat, and they can't really process much power.  The 813's with
their graphite plates can handle a lot of power.

Staccato operation can be rough on tubes at times and can promote
flashovers inside the tube under certain conditions.  I never tried the
813 with staccato.  Still, it's quite possible that the 813's will work
very well with staccato.  Since the 813's have a screen grid, you have
to either tie the grids together, or run the screen grid from the main
power transformer using a high resistance large wattage dropping
resistor.  Usually folks try to avoid using tetrodes or pentodes for
VTTC's in order to keep things simple and robust.  The thinking
is that the less grids there are, the less there is to short out and
burn up.  A very common tube for VTTC's is the 833A or 833C.
The 833C has the graphite plate.  Using 833A's or C's, one need
not over-volt the tubes so much as is the case with some other
tube types such as the 813, 810, 805, HF300, VT-4C, HF200, 803,
etc.  There are other tubes that can be used such as the 3-1000A
(expensive), and the 4-1000A.  This last tube seems to be subject
to various failure modes, but it has a 6kVDC rated plate voltage.
Then there are water cooled tubes, external anode tubes, etc.
Another interesting tube is the 5868 industrial triode.  Then there's
the 4-125A, 2-250A, and 4-400A tetrode designs.  These are not
as robust as an 833A or C.

I show some tubes and VTTC's at my website at:

    http://futuret.110mb.com

Cheers,
John


-----Original Message-----
From: Grant Visser <freeekyg@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Mon, Jul 13, 2009 6:36 am
Subject: [TCML] Choice of tubes for first VTTC?



Hi all,

Have been thoroughly enjoying my NST driven SG coil over the last few 
months
(pushing 1.3/1.4 m sparks) and would now like to try my hand at a 
decently
sized VTTC.

The only tubes I have found locally so far are the 811A and 813A's. I 
have
seen the 811A's mentioned quite a bit on the list but not a single 
mention
of the 813A. To my heavily untrained eye the 813A looks like a great 
little
tube (3 grids?) but thought I'd ask your advice before I go out and 
blow my
non-existant budget. lol

813A:
DC Plate Voltage = 2250V
Plate Dissipation = 100W
Datasheet: http://www.mif.pg.gda.pl/homepages/frank/sheets/079/8/813.pdf

I'd like to push as much power as possible into a 160mm (6.3") coil at 
300
to 350Khz, with dual or even quad tube configuration, staccato control 
and
possible audio modulation.

Best regards
Grant
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla

_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla