We are mostly in agreement.
I don't have any footnotes or sources to cite; however, my perception is
that receiving tubes run within ratings may easily exceed 10,000 hours
or more useful service with some going much much longer. FWIW, I
recently retired a CRT television that by calculation well exceeded
50,000 hours CRT time. The CRT is not what failed.
I agree that multiple "turn on" thermally stress the tubes especially
transmitting types where the turn on surge in some larger tubes must be
managed to avoid immediate damage. Very large tubes benefit from
filament voltage management where the minimum cathode temperature to
provide adequate performance is determined after several hundred hours
break in.
If I don't intend to use an older tube radio for at least several hours
I don't turn it on. I use the solid state rig instead. For me this is
the balancing point.
Transistors do degrade over time as the crystalline structure breaks
down and various materials migrate. But you will probably never notice
that unless it is a power type that is run hot speeding up aging. At
cool temperatures something else will fail before the transistor.
May we all have the time and health to use up and wear out our radios.
Pat
wa4tuk
On 12/17/2015 7:59 PM, Charles H wrote:
On this reflector, I have poo-pooed the idea of baby-ing your radio especially
by turning it off often, lowering xmit power, etc.
However, I read that with ordinary tubes, the chemistry of the cathodes and filaments are affected
by life-of-use, so that tubes do "wear out" with use. Tubes can be rated in terms of
"hours of use" with the type in a KWM-2 rated at around 2,000 hours of useful function.
Thorium in the chemical make-up of the metal parts in a tube, maybe a metal or ceramic tube
(usually added to higher power tubes) can extend tube life to about 100,000 hours.
The conclusion is that "hours of use" of course do matter for hams intending to use their
tube-type radios for thousands of hours. The hours of use can be limited by simply turning the
tube off when having only stand-by function. However, there is some suggestion in the literature
indicating that every "turn on" of a tube (or an incandescent light bulb) involves rapid
heating of the elements inside which could, immediately or over time, deform elements and causing
sudden failure (given that the metal elements do heat unevenly--due to resistance in the metal--if
only for a very short duration of time). Repetition of on-and-off cycles are thus a factor in
lower tube life.
Other than these factors, it appears in the literature that operating a tube,
particularly high power transmitting tubes, at its rated values can extend life
IF it is otherwise not sometimes operated below or above its ratings. It
appears that, for example, driving an RF amplifying tube at its full rated
power does not materially decrease its life. Reducing drive appears not to
extend such tubes' life.
It is all a balancing act. 73, Charly
P.S., next question is "do transistors 'wear out'?"
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