> I don't have an answer but your post and a couple others I've seen beg this
> question. What is all this worrying about how many times a 3-500z is turned
> on and off?
>
> My ancient Eimacs could care less. What am I missing here?
>
> 73,
> Steve wd0ct
One of the main issues is inrush current, Steve.
This is the reason most light bulbs fail upon turn-on.
If the filament transformer is designed properly for the tube(s)being powered,
the inrush current is self-limiting to less than the tube manufacturer's specs.,
and you have built-in protection and long tube life. If the current capability
of
the filament transformer is in excess of a tube's rated maximum inrush current,
a step-start circuit can be placed in the primary of the transformer. If the
output
voltage is too high at the tube pins, a power resistor or rheostat can be
placed
in the primary of the transformer which will allow adjustment of voltage and
also
limit inrush current. This method has been used by Henry and other manufacturers
in their commercial amps and RF generators for many years.
We have had "line voltage creep" here in Texas, and I expect elsewhere, over
the years from 112-115 volts to over 125 volts, such as I have here in my shack.
Even light bulb manufacturers are now offering bulbs rated at 130 volts.
Since tube ratings are fixed, it is necessary to adjust for the increased line
voltages
from time to time in order to obtain the advertized tube life. Each spring,
during my
amp cleaning and blower oiling ritual, I measure filament voltages at the tube
pins and
adjust accordingly.
(((73)))
Phil, K5PC
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