[Amps] 1200 vs 1500 triodes

[John T. M. Lyles]

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