Re: Toob coil questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steven Ward" <srward16-at-hotmail-dot-com> 




> > >16" is a LOT from a pair of 811As... the coil may be designed to drive the
> > >tubes far beyond their ratings... You better watch that the pates DO NOT
> > >get even a bit of color on them.  If they turn red at all, you are pushing
> > >things hard!
> >
> > Oh!!  I did note that the red hot area was sort of a concentrated hot
> > spot...  Thanks!!  Now I know what I am seeing is real and scarry...
>
>         That criterion is a little conservative.  Operating 811's or 
> 812's with
>a red or even orange spot in the middle of the plate isn't going to
>destroy the tubes if you don't run them for more than a few minutes at a
>time.  I've run a pair in a ham transmitter with the plates showing a
>definite orange in the center and never experienced failures.
>
>Ed
>


Well, with VTTCs we have a few things to watch out for.  Red plates promote 
tube arcs from what John Freau has told me.  An arc to a red plate may very 
well destroy it.  Im assuming that since an 811A was not meant to run with 
color on the plate, one should strive for that.  But, with say the 304TL i 
have, which is spec'd to run with a dark red plate, is a completely 
different story.  If the tubes get red quick, it might be a good time to 
look into a staccato controller.  Either that, or get a smaller tank cap so 
that you can up the impedance of the tank and lower the current draw.
Though, you will lose spark lenght.

Steve