28 Jul
2007
28 Jul
'07
7:44 a.m.
It's probably not a bad idea to limit inrush
current, however. A
surgistor will do that trick.
Limiting inrush is useless for nearly every tube made, as the
filaments are made to deal with it anyway. The only tubes I know of
that required some sort of inrush protection were a few of the very
large transmitting types from the 1940s - the kind whose filament
current ratings are in the hundreds of Amps. Some of them even had
specific power up and power down sequences. With some of the huge
tubes later on, there was inrush protection, but that was to protect
the transformer, not the tube.
I seem to remember it's also advisable to let
mercury-vapor
rectifiers that haven't been used for a long time "cook" without
plate voltage the first time they're used (beyond, that is, the
initial normal warm-up time).
Yes, the dreaded flashover. Every time a mercury rectifier is powered
on, it should go thru the ten-minute (or so) cycle, to make sure ALL
of the mercury is vaporized before high voltage is applied.
As far as I know, computers did not use mercury vapor rectifiers. In
all the ones I have seen, or seen documents for, the rectifiers have
been gas types. When I was recently poking my nose into Pierce's 709
power unit (7mumblefoo?), I saw that IBM used C16J thyratrons - a
whole flock of them. Which probably makes that power unit the most
costly piece to retube these days.
--
Will