>On Fri, 12 Dec 2003, R. Measures wrote:
>
>> >I have to learn to be more careful though - i've been sloppy keeping
>> >the grid current under 260mA when tuning.
>> >
>> ** 3-500Zs have no grid-I rating. They have a grid-dissipation rating
>> of 20w -- which can be exceeded (as in glowing grid wires) for brief
>> periods without damage. Grounded-grid/cathode-driven amplifiers should
>> not be adjusted with the grid-I meter. Instead, they should be tuned
>> with max rated drive, preferably pulsed, and adjusted for max P-out with
>> the Tune and Load controls. With P-out peaked, grid-current will always
>> be ok because excessive grid-I will always rob electrons from the
>> output.
>
>I wonder why grid current is measured instead of dissipation -
** Grid-I is usually defined as average indicated current on a typical
meter. A system for measuring actual dissipation would be considerably
more complex. In any case, grid-dissipation is not a problem when an
amplifier is tuned for max-P out instead of max grid-I.
> I would
>think dissipation and current measurements could be easily interchanged
>for display on a meter.
** Hardly. Grid-I looks nothing like a sinewave because it only flows
when the grid is positive, which is less than half of the driving cycle,
and even then grid-I is not at all proportional to voltage.
> ...
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