Tom said:
>This effect is essentially the erosion of the filament metal.
This is my worry, too. In semiconductors, it's called 'metal migration',
and it goes faster as the temperature goes up. For my 4CX1000, I'm using a
constant current supply for the filament, set so that equilibrium is
reached at the correct filament voltage: this avoids the problem of inrush,
and mains variations. To get around the metal migration, I have a simple
circuit using a latching relay which reverses the polarity on the heater
every time you switch on.
(It actually use a total of three relays (one latching), two electrolytics,
a diode and a resistor - I expect you could do it all solid state if you
tried, provided you had some non volatile memory)
73
Peter G3RZP
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