> From: dtrbizan@netcom.ca
To: <amps@contesting.com>
> Date: Tue, 29 Jul 97 04:09:10 +0000
> I,ve recently obtained a number of new surplused 4PR1000A tubes and
> promptly began to put together an amplifier using a pair of these tubes.
> Using 5500v on the plate, I found that they require a fair amount of
> drive.
Hi Dave,
The gain of a grounded grid PA is greatly determined by the ratio of
cathode impedance to anode impedance.
I'm afraid there is no cathode driven (grounded grid) configuration
that will change the fact the 4PR1000 has a high driving impedance,
so the tubes will always have low gain in grounded grid.
If you want to drive them easier, you need to either raise the HV
(and then the tubes will get very unstable) or use grid voltages and
grid drive the tubes. A pair of tubes (even with the grid
swamped) should probably be neutralized, if you want to use them on
21 and 28 MHz.
My old pair of 4-1000A's made about -30 dB third order in class AB2,
and about -32 dB third order IMD in AB1. That's better than most
modern radio, even though it is not near what a modern GG
focused beam triode (-40 dB or better) or 3CX3000A or F7 will do.
73, Tom W8JI
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