>I expect that 99% of tube flattening is caused by operator abuse and 1% by
filament overvoltage. This ignores those >amplifiers which use 6 volts on a 5
volt
filament because they are defective and merit no further discussion.
>Colin K7FM
There is a graph somewhere on the web, I think, that was referred to on this
reflector
that shows tube life vs filament/heater voltage. The graph does not begin at the
top
of the tolerance, but at the nominal rated voltage. Just a few tenths of a volt
over
nominal starts to reduce tube life. This grows in an exponential manner, so that
even if the voltage remains within the manufacturer's tolerances, the life of
the
tube
is greatly reduced.
I suggest that filament overvoltage is a CAUSE of tube flattening, along with
operator abuse and inrush current. A tube can be flattened by filament abuse
long before it burns out. The fix is simple and cheap, as you have stated.
You are lucky...many of us in N. TX have well over 125/250 volt mains.
I have owned/repaired/tested many brands of amps over the years, and all
required lowering the filament/heater voltage with this amount of mains voltage
that I have here.
(((73)))
Phil, K5PC
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