[Amps] 8877 Longetivity

[Tom W8JI]

> 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