> This is a sad day in amateur radio. Here we are in a mail list for the
> high end of the amateur radio building community and we're reluctant to
> use a tube that requires bias!? 4-1000's look ok when glowing orange but
> an 833A is gorgeous with that bright red region in the center of the plate
> (not anode, plate).
The problem is the tube will have low gain. That's because the gain
of a grounded grid PA is related to the ratio of output impedance to
input impedance of the tube.
With it's low-mu construction, the 833 would take a heap of voltage
swing on the input meaning driving impedance would be high and
gain would be very low.
It would be OK to grid drive the tube, but then stability becomes an
issue. The IMD also goes up because the heavy negative feedback
inherent in cathode driven systems (the output is in series and out-
of-phase with the input) would disappear.
The tube could certainly be used, but it wouldn't be a good choice
(especially since they have long leads and are prone to self-
oscillation at upper HF).
73, Tom W8JI
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