RE: VTTC ponderings. (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 7 Aug 2007 11:21:43 -0500
From: Rich & DJ <rdj@xxxxxxxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: VTTC ponderings. (fwd)



-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx] 
Sent: Tuesday, August 07, 2007 7:52 AM
To: tesla@xxxxxxxxxx
Subject: Re: VTTC ponderings. (fwd)


---------- Forwarded message ----------
Date: Tue, 07 Aug 2007 08:21:17 -0400
Dave , Scott is right on about the filament transformer. It is the one thing
on a tube that has to right. I have some tubes that operate on any where
from about 2000 to 30,000 volts on the plate but the filament must be 5.0
Vac , too low and you loose emissions to high and it shortens the life of
the tube a lot. A question was asked about big VVTC , well if you look at
the Eimac tubes offered on e-bay you are only limited by you pocket book. I
am a ham radio guy and mess with tubes a lot but if you want to go to high
power a pole pig and regular coil is a lot cheaper. I have made my own
filament transformers , it is easy to do.

Rich , Kd0zz 


From: David Speck <dave@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: VTTC ponderings. (fwd)

Scott,

Most folks run their VTTC MOTs from a Variac.  If you were getting your 
filament voltage from a winding on the MOT, then the filament voltage 
would also vary as the HV varies.

Most vacuum tubes work best in a narrow range of filament voltages.  Too 
low, and emission drops way off.  Too high, and life is drastically 
shortened.  Some VTTC builders take pains to keep their filament 
voltages within a few percent of nominal. 

Separate transformers allow a constant filament voltage with a variable 
plate voltage.

Some experimenters have built DC driven VTTCs, but the reported 
discharge pattern is a rather uninteresting bushy hissing corona-like 
display.  Apparently, the intermittent nature of the half wave 60 Hz 
pulsations changes the dynamics of spark development.  The staccato 
circuits have made the display even more interesting, even though they 
actually power the circuit LESS than every other half cycle.  Sometimes, 
more is not better. 

Dave

>   Firstly, why does everybody use a separate transformer for their
filament,