Re: VTTC ponderings. (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 07 Aug 2007 08:21:17 -0400
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,