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Re: VTTC snag
Original poster: "Area31 Research Facility by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rwstephens-at-hurontario-dot-net>
Try reversing the connection polarity of your grid coil. It may be introducing
negative feedback which would not cause any oscillation and no tube current.
You want positive feedback. You could also swap leads on the plate coil and
achieve the same result but this may not be as convenient or desirable. I like
to have the tube plate terminal at the very top of the tank winding. I would
increase the grid coil to 1/2 to 3/4 as many turns as the tank and locate it
below the tank coil, not above. It will see less e-field down there. It
doesn't need e-field.
It sounds like the small mains current increase you are seeing near the top of
the variac is just saturation current of the MOT. To check this disconnect
everything from the secondary of the MOT and see if this current rise still
occurs. If it does it is normal. They are stingy with the core iron in these
> ----- Original Message -----
> From: <mailto:tesla-at-pupman-dot-com>Tesla list
> To: <mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
> Sent: Saturday, July 14, 2001 14:04
> Subject: VTTC snag
> Original poster: "Sundog by way of Terry Fritz
> Hi All!
> Well, it's been an unproductive few days, in the aspect of sparks.
> here's the delimma. I have double and triple checked my setup, but can't
> the reason it's not working. I should get *something* happening, even if
> letting out the smoke from something. Here's the specs
> 1800v MOT, voltage doubled. it'll easily pull 12A on the 120v line, so
> plenty of power available
> secondary is 21" winding of 26ga wire on a 4A green PVC pipe. unloaded Fres
> primary - 37 turns of 14ga THHN on a length of 6" white PVC (6.5" OD), quite
> few taps on it for tuning
> grid coil is 12 turns of 22ga hookup wire, about 3/4" above the primary - it
> can be moved up or down
> tank cap is a 5nf (4.89 measured) MMC, grid C is a 2.5nf MMC, grid R I have a
> selection of resistors to try. They'll smoke in short order, but it should
> for enough to get a result.
> Running 2v into the variac, I get 16v out of the MOT. I get roughly 32v at
> top of the tube. Mkay. Doubler and whatnot seems to be working okay, I'm
> getting voltage.
> When i crank the variac to about half-throttle, i get *no* increase in
> to the MOT. I shut it all down, short the MOT, then crank the variac to half
> throttle again. Draw is about 7A. Oooookay... Hook the coil back up, and go
> to 5nf for the grid C. Finally I get some current through the MOT, but only
> ~2A :/ I'm going to try 10nf for the grid cap, but I think I see the
> already, - not enough turns for the grid coil. But that's a bit odd, as you
> drive the grid current up to shut the tube off..so the tube shold go full on
> when I begin applying power, but until I went to a larger crig cap, nothing.
> I'm going to resume tinkering. The good thing is that I'm on vacation all
> this week, so I got a whole week to mess with it :)
> Laters Shad