Re: Necessity of NST Protection Filters and Safety Gaps

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

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi Luke.

 > Original poster: "Luke" <Bluu-at-cox-dot-net>
 >
 > May I ask why inductors are not used instead of the resisistors since
 > the react with frequency?

Inductors were used in the past. The problems with them was resonances
causing problems.  The RC filter is a proven design.

 >
 > What is a MOV?

Metal Oxide Varister (glorified zener).  In the Terry design they are 1800V
and will conduct 2000 amps.  They will give their ALL to protect the NST.
Failure mode is short.

 >
 > And what is the method to properly set the safety gap?

Safety gap is a 3 terminal gap (outer posts connected to the 2 hot leads
between the terry filter and the main gap, the center post connected to the
NST chassis.  This gap is adjusted with the TC primary and Cp disconnected
from the NST and is adusted to either "just not fire" at no load output of
the NST driven at 120 Vac, or set to "just fire" with the variac set to say
130 Vac.  Once you've done this procedure before run time, you don't need to
worry about setting the main gap too wide.  The safety gap become your
backup.  I usually set my main gap wide enough to where the safety gap fires
occasionally.

 > Are you talking about the safety gap at the Main spark gap or the safety
 > gap in the NST protection circuit?

I believe these safety gaps are one of the same.  Keep it close to the NST
(with the Terry filter) if the NST's are located away from the main gap.

Gerry R
Ft Collins, CO

 >
 > Luke Galyan
 > Bluu-at-cox-dot-net