>Hello all,
> My friend and I are contemplating a monoband amp based on the
>3CX3000A7 tube. A look at the Eimac spec sheet shows 410 Watts drive for
>AB2 Cathode driven.
>
>This doesn't seem very practical if you only have 100W of drive. On to grid
>driven AB2 specs. They show a very conservative output of 1.13KW with 11.5W
>of drive. Surely it can be driven a bit harder than that.
With a high Mu (200) triode, if one drives the grid hard, the SSB output
is hardly clean.
- You can drive a 3cx3000A1 (Mu=5) at the grid in linear service,
however, it is not a piece of cake. If you need serious suds, an 8171
tetrode will take you there with less overall complexity. The typical
power gain is 100 instead of 15 to 20.
>The output figure
>for cathode driven is 7.26KW! What are the limiting factors of a grid
>driven amplifier using this tube. I mean if you are going to burn over 350W
>just to run the filament, surely you would want to see more than 1.13KW out.
>
For linear service, high Mu triodes work best in cathode driven config.
>We would like to try and put 100W on the grid. What sort of input circuit
>would we need? Does anybody know the zero signal plate current? Would we
>need neutralising?
>
For cw, ok, for ssb, not ok.
>Our alternative is to use a driver stage like a 4-250A or the like but we
>feel that it would complicate things.
>
'Tis a good buffer. However, use a tetrode for the final and you won't
need a buffer. Fair Radio Sales has an ideal 5uH Collins roller coil for
grid tuning large tetrodes. It costs $10. Another surplus dealer sells
it for $35. It is fairly worth c. $60.
- later, Alek.
cheers
Rich...
R. L. Measures, 805-386-3734, AG6K
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