[Amps] 8877 Longetivity

[Paul Christensen]

> Given the relative low accuracy of normal AC panel meters, how can you be
> sure that you are actually within the filament voltage tolerance specified
> by the manufacturer?  A high accuracy AC meter is a rather large and
> somewhat expensive animal.

One method I've used is to add high-quality test point jacks to the amp's 
front or rear panel.  Low-wattage metal-film resistors of 1K-ohm or so can 
be used to isolate the filament connection from the test jacks in the event 
a fault occurs during measurement.  This allows the use of a high-quality 
DVM (e.g., true RMS) meter to be used only when needed.

Since a DVM is a high-Z sampling device, the isolation resistors essentially 
play no part in measurement accuracy.  I have a Fluke Model 189 DVM and it's 
used as my general purpose shop instrument.  This eliminates the need to 
tie-up an expensive meter just for filament measuring purposes.

Paul, W9AC