> For a.c. RMS volts I use a Fluke 89-IV DMM with a.c. RMS
> display. Most any panel meter will be useless because of
> inaccuracy,
> because of residual magnetism inside it screwing up the
> accuracy,
> and mostly because fifty millivolts either way might mean
> hundreds
> of hours more life for your tubes.
Hal,
Respectfully your claimed result is just not correct in this
application. The only thing reduced filament voltage does is
improve filament or emission life, and it ONLY improves
those things in an amplifier that operates the tube well
below limits and without frequent thermal cycling.
If you use normal ICAS amateur service any change you would
make would be lost in the noise of all the other problems.
This entire filament voltage issue has been blown way out of
proportion by taking accurate valid concerns in one
application and without thinking apply them to another
totally different set of operating circumstances.
The failure rate for emission loss in a tube in amateur
service is next to zero, while failures caused by thermal
cycling, gas, and element shorts account for nearly all
failures.
It's like me taking my wife's cars (which she wrecks like
clockwork every few years (totals in 1994, 1998, 2000,
2003)) in for 3000 mile oil changes and expecting the
failure rate to decrease over oil changes every 10,000
miles. The type of service and operation is critical, and
the data you are using for claims of increased life comes
from 24 hour days 365 days a year constant operation far
below ratings with tons of air where nothing thermally
cycles or gets momentarily overloaded. That is not our tube
application, just as 35MPH while watching the road carefully
is not my wife's operating mode with her car.
73 Tom
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