I have a dozen dvms around. My top end dvms include two Flukes and a
Hewlett Packard.
One day, I decided to test the accuracy of my meters (only on dc voltage and
resistance). I was surprised to see that a meter I purchased at Harbor
Freight for $3.95 was the equal to one of my Fluke meters (I did not have
the other one at the time). I did not find a bad meter among them.
The accuracy of any of them far exceeds my needs, and is probably much
greater than is necessary in most cases. For example, if a tube specifies
5.0 volts, that is based upon a nominal standard. In fact, each tube would
likely have a different optimum filament voltage that may vary by at least a
few percent. Likewise for screen voltage. If a tube is specified at 250
volts, that is a nominal voltage. I would expect that the "perfect" voltage
for that particular tube could only be determined by creating curves for
that particular tube. Without those tests, 260 volts would be just as
likely to be the correct voltage as 250. What would be important would be
regulation. And for that, resolution and repeatability of the meter 1is
more important for measuring than absolute accuracy.
Even the cheapest digital volt meter is likely to exceed the accuracy of an
older analog volt meter.
I remember using my Fluke to adjust an adjustable 5.00 volt regulator to run
some integrated circuits. Getting exactly 5.00 volts was touchy with the
miniature pot, yet I played the game. However, it is hard to abandon
adjusting at 4.9 or 5.1 volts. I chuckled at myself as I continued to try
to attain perfection. What I needed was a simple led system that lit when
the magic "close enough" was reached.
73, Colin
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