Marv,
My suggestion for long service life in this scenario is based on
minimizing peak inrush currents, especially considering the large number
of startup cycles you are going to have.
By experiment, determine the minimum "idle" current necessary to
substantially reduce the normal start-up peak inrush current. If the
cold inrush current is say, 10X the normal filament current, increase
the idle current until the peak inrush current on going to full voltage
is less than 2X the normal filament current.
As an example scenario, assume normal current is 100mA and peak inrush
with cold start-up is 1 A
Adjust the standby voltage until the switch to full voltage only results
in a 200mA (or less peak current)
There will be a tradeoff involved here. The best balance is minimal idle
current and substantially reduced peak current.
--
Gerald Boutin, VE1DT
This concerns somewhat smaller tubes than are typically discussed on this
reflector but, where else can I hope to find someone old, errr... experienced
enough, to know the answer.
Given an old miniature tube with a 1 volt filament and a (stated) 10,000
hour service life.
And an application that requires the tube to be active for slightly less
than one second per minute.
Is it reasonable to idle the tube with some percentage of its rated heater
voltage applied, bringing it up to full voltage periodically, with the goal of
substantially increasing its service life?
And if so:
What percentage of the rated heater voltage would be optimal for the
"standby" period?
How much increase in service life may be expected?
Note that the directly heated filament acheives operating temperature in a
fraction of a second from a cold start.
73 & Good morning,
Marv WC6W
http://qsl.net/wc6w/
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