Re: Counterpoise and MMC demise

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

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 11:45 20/06/03 -0600, you wrote:
>Original poster: "Finn Hammer by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><f-h-at-c.dk>
>
>Stephen.
>
>I am sorry to hear of your loss, but there is no reason to add to the
>myths, such as that the breakdown voltage of a static gap suddenly
>increases. It doesn`t.


First of all I must admit, you are right. I have no scientific proof that 
my NST died _because_ of overvoltage. It could have been stray RF (I wasn't 
using any kind of filter :( ) or just an old tired NST that was about to 
fail anyway :[

However, I have read a few books and articles on high-voltage physics and 
they all talk about randomness in the breakdown voltage of spark gaps. The 
voltage, and delay time, depend on a whole bunch of things, like 
temperature, humidity, pressure, radiation, etc. The graphs show a voltage 
that varies randomly, so it's as likely to get bigger as it is to get 
smaller. In high-voltage lab experiments they apparently use UV lamps 
shining on the experiment, or a radioactive source, to stabilize the 
breakdown voltage.

Also, even if the individual gaps were totally repeatable, a multi-section 
gap could still cause trouble because the middle sections are floating, so 
the field profile depends on poorly defined things like capacitances, 
corona, and leakage currents in the insulators. If you set it on a damp 
day, it might have a higher voltage on a dry day.

But whether any of these effects were at work in _my_ spark gap, I couldn't 
say. Anyway I don't miss the NST, my new DC power supply has 4 times the 
output and so far none of those 68 diodes has blown :)

Steve C.