I vote for the 3CX1500A7/8877-based amplifier also. I helped design
an FM broadcast amplifier using it in 1983, and it easily produced
1500 watts of CW output class C at 108 MHz. Last year I converted a
RF Power Products plasma generator from 13.56 to ~4-5 MHz for a
scientific application. It had a questionable old tube in it, as it
was pulled from another experiement in a different lab. When I
finished, it fired up immediately at 1200 watts without a burp, no
'gas', no 'oscillations', very stable.
That tube has a myrad of applications, and even though expensive, it
is a good part. There have been periods (as with many tubes) where
the mfr had a production glitch. However, based on the limited
application of the 3CX1200 in ham amps, and the domination of
commercial and scientific/medical/military apps for the 8877, the
answer is fairly obvious.
John
K5PRO
The difference between the '1200 and '1500 in feedback
capacitance is only 2:1, and both are very small,
indeed. While there are the occasional reports of
oscillations with the '1200, it is more likely a
result of the long element leads inside the tube, and
not a result of the 0.2pF feedback capacitance. The
3CX1200A7 data sheet shows the in/out/feedback
capacitance when operated in grounded cathode, and
Rich appears to have not converted that data into
grid-referenced data.
However, the feedback capacitance information has
absolutely nothing to do with your original question.
Were it my amplifier, I would choose the 3CX1500A7
immediately. I have seen the 3CX1500A7/8877 used as a
driver in many broadcast applications, and as a final
in many scientific applications. I have never seen a
3CX1200A7 outside of a ham amplifier, ever. The 8877
is popular enough that, at least at one time, it was
available from Chinese sources.
73,
Dave W8NF
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