Re: First VTTC light, and a few questions

["Grayson B Dietrich" <electrofire-at-juno-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

On Fri, 21 Jul 2000 08:11:12 -0600 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: FutureT-at-aol-dot-com 
> 
> Grayson,
> 
> Yes, it might be possible that the RF is simply affecting the meter
> reading, but not really raising the voltage on the filament.  If the
> filament voltage is really increasing, then it should get visibly
> brighter as the voltage rises.  I don't use center tapped filament
> transformers either.  I do use a bypass cap from the ungrounded
> side of the filament to ground.  I used to use a clamp-on ammeter
> and it read 50% higher when it was physically near the TC.

OK, glad to hear that. I had been a little worried about damaging the
filament.

> 
> Are the output sparks long and straight, or kind of fuzzy, just
> curious.  

part way between. I have to decrease the grid resistance to far less than
would run the tube under specs to get them really strait, and yes, they
are longest then. 

I often obtain the longest sparks when they are straight
> and sword-like.  This is affected by tuning and other adjustments,
> as well as by the Q of the secondary it seems.  Are your 811A's
> new or used? 

New!

 If used, they may have low emission and don't 
> have enough emission to ever get red. 

They have gotten red before, when the grid voltage was something higher
than 150 (pegs meter) and the coil was running very badly.

 If you can increase your
> input voltage from the plate transformer, this would help to redden
> them if they have sufficient emission.  Did you try running off a
> 140V output type variac? 

Actually, I wired a MOT in to see what would happen. I can't get as long
of sparks off of the same voltage, but, I can increase the voltage way
above that and get decet operation, with the plate reddening just a
little. Do you think I could safley run the tube (rated at 1500V) off of
a 2200V MOT? I usually don't turn the variac up past 70% ( it is scaled
to 100, rather than a voltage scale), but the arcs are nice and long (4")
when i max it out. The grid voltage is okay then as well as the plate
current. 

 I've never used 811A's myself, so I'm 
> not all that familiar with their capabilities or behavior.
> 
> Assuming you have good tube emission, another way to increase
> the plate current is to reduce the number of turns in the primary
> and use a larger cap to tune.  Higher voltage operation is more
> efficient though.

And so I have seen ;-)   My friend just bought a really nice ($150)
webcam for his laptop...   ...would you think using it to take
video/stills  (it has an adjustable shutter rate, 1/50s to 1/4s!, can see
in near complete darkness) of this coil would be advisable? I would trust
it with a spark gap coil of this size, but, I know that VTTCs give off
more RF energy...    ...what would you do?

> 
> Cheers,
> John Freau

Thanks,

Grayson Dietrich
http://www.electrophile.8m-dot-com


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