"the idea of the filaments being turned on and off worries me."
When you go into the bathroom for a few moments and turn the light on, you
are "wasting" the filament of the light bulb. But, you balance the
usefulness of the light in aiming with the ultimate destruction of the bulb.
It is similar with the filament on a tube. I get into my car and drive the
1/4 mile out to get the paper or mail, even though it is probably not good
for the car.
One thing you can do to lessen the shock of the filament heating is to make
sure the turn on current is not so great that it will stress the filament.
Many commercial transformers are automatically limiting, so no further
protection is necessary. You can measure the filament voltage at the tube
socket and make sure it is within specifications of the manufacturer. And,
with a current probe and a scope, you can measure the instant turn-on
current rush.
I remember visiting a friend many years ago. His father had some WWII
radios still in the crate and the son wanted to show them to me. The father
was a strange dude and in front of me he gave his son a lecture about
turning the light switch on and off, because it would cause the light bulb
and the switch to fail. Years later, I saw the kid again and asked about
the radios. He said they were thrown out when his father died from a heart
attack. I forgot to ask about the light bulb or the switch. However, it
seemed that in the ultimate scheme, turning the light bulb on and off was
not that big of deal.
73, Colin K7FM
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