>>The best solution is to mechanically adjust the meter needle
>>further up-scale toward the center. As well as the front-panel
>>screwdriver adjustment, many meter movements have a coarse
>adjustment on
>>the rear pivot.
>
>REPLY:
>
>The "best" solution?
>
>How is that better than simply using a zero-center meter in the first
place?
>Your method gives a reading that is constantly in error by the amount
of
>off-zero adjustment.
>
>73, Bill W6WRT
Most tetrodes run relatively small amounts of negative screen current,
and only at moderate drive levels and light loading. As the drive and
loading are increased the current becomes considerably more positive, so
an optimized meter scale will display zero screen current at about
25-30% of full scale.
The 4CX1000A is one of the few types for which a true center-zero
movement might indeed be the most appropriate... but good luck with
finding one that matches all of the other meters on the panel *and*
already has the correct scale.
Amateur amplifier builders may be able to find a matching set of meters
at reasonable cost, but in the large majority of practical cases, most
of those meters will need to be re-scaled. Custom scales are no problem
today, thanks to the 'Meter' program by Tonne Software
(www.tonnesoftware.com). This program can easily create a custom scale
for the screen current meter, optimized to display a moderate amount of
negative current but a larger amount of positive current.
73 from Ian GM3SEK
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