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[AMPS] SB-1000 mods?

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Subject: [AMPS] SB-1000 mods?
From: Ian White, G3SEK" < (Ian White, G3SEK)
Date: Wed, 12 Sep 2001 22:33:48 +0100
2 wrote:
>>2 wrote:
>>>//   The purpose of the glitch-R is to protect the electron tube from 
>>>failure during an intermittent oscillation condition. 
>>Make that "...from failure due to a current surge occurring for *any*
>//  Please name and explain some other causes of potentially fatal 
>current surges, Mr. White.

You appear to have forgotten that this very subject was discussed at
some length back in January/February. 

Here are a few quotes from the literature.

"Although a very high degree of insulation between two electrodes can be
obtained... by modern high-vacuum technique, it is nevertheless possible
for this insulation to break down spontaneously and completely. This
phenomenon is known by various names, such as... the "Rocky Point
effect", after the American wireless station, which is one of several at
which it has been observed. ...  Time lags [after application of
voltage] can vary between a few seconds or minutes to tens, hundreds or
even thousands of hours." 
Gossling (British GEC), 'The Flash-Arc in High Power Valves', 1932.

"Most power tubes are subject at some time to a phenomenon known as the
Rock Point effect, which derives its name from experiences with power
tubes in communications transmitters at Rocky Point, Long Island.
This phenomenon manifests itself as  an internal flash-arc developing
with little warning on power tubes which apparently are of good design
and operated in a conservative manner... The cause of this phenomenon is
not thoroughly understood..."
Parker and Hoover (RCA), 'Gas Tubes Protect High-Power Transmitters',

"An arc is a self-sustaining discharge of electricity between electrodes
in a vacuum environment...  Since any high voltage vacuum device may arc
at one time or another..."
Eimac, 'Fault Protection', Application Bulletin #17, 1987.

Those are only about the arcs that can occur *inside* tubes. Current
surges can also occur due to HV shorts outside the tube - remember the
earwigs?  These outside surges will not damage the tube but they can
certainly damage the power supply and metering circuits.

As I said, it's best to keep an open mind about the causes, but by all
means protect against the effects.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)

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