>Does anyone have any idea on the length of time that big (i.e. 1MW + )
>tubes take to heat up the cathodes, from the time filament voltage is
>applied ? A friend asked me, thinking I would know, but needless to say
>I have never looked at a data sheet for any of the really bid devices.
>
Eimac 8973 specifications 7/1/78, page 4
(the 8973 has a 18.5V-nom. 650a filament, and the anode/plate is rated @
65A and 22.5kV.)
"Filament turn-on and turn off should be programmed in accordance with a
special procedure; filament voltage should be increased from zero to the
operating level over a period of two minutes and a motor driven VARIAC or
POWERSTAT is suggested. Inrush current must never be allowed to exceed
twice the normal operating current Turnoff procedure should be a
smooth decrease from the operating voltage to zero over a period of two
minutes, such as would be provided by a motor driven VARIAC, POWERSTAT or
solid-state regulator circuit.
Filament voltage should be measured at the tube base with an accurate
meter. When operating at the nominal voltage, variations of +/- 5% have
little effect on the electrical performance of the tube. When very long
life and consistent performance are a factors, the filament voltage can
often be reduced to a lower value than the nominal, but should be
regulated and held to +/- 1%.... "
{note: For maximal emissive life, the filament potential should be
reduced to a point about 1% higher than the point where a slight decrease
in power output is observed. The same thing applies to all thoriated
tungsten filament tubes.}
cheers, Dave
Rich...
R. L. Measures, 805-386-3734, AG6K
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