On Tue, 19 Sep 2000 15:44:38 -0400 Ken Barber <kbarber@monmouth.com>
writes:
>
>Hi,
>? I need some help understanding tube specs in the VARIAN tube catalog.?
In
>RF LINEAR service the 3CX1200A7 has an amplification factor of 200 and
needs
>85 watts drive, the 4CX3000A has an amplification? factor of 5.5 and
needs
>only flea power drive.? Can someone unravel the mystery for me?? Also
when
>they show the amplification factor as (g1-g2), what does this mean?
>Thanks,
>Ken W2DTC
>?
Hi Ken,
Without looking...
The specs for the 3CX1200A7 are probably being given for grounded grid
usage -- most of that stated drive power actually ends up going out the
plate circuit and to your antenna.
The 4CX3000A specs are likely given in grid driven AB1 configuration
which requires next to zero drive power, neglecting circuit losses. The
(g1-g2) amp factor represents only the relative effectiveness of the
control grid vs the screen grid in controlling plate current. The real µ
of that tube would be up around at least 1000, speaking in "triode"
numbers.
If you can get a hold of a copy of "Care & Feeding of Power Grid Tubes"
by Eimac, later Varian, now... oops, it escapes me at the moment who owns
Eimac now... you should find a more complete explanation than my fingers
are good for at the moment. I believe that the text of that book is also
posted on the Eimac website.
And, of course, any of the old Terman books (pre-1960) should cover
these subjects in depth.
73,
Marv WC6W
*
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