ORIGINAL MESSAGE:
On Wed, 08 Aug 2012 21:50:42 -0700, you wrote:
>
>Because as I understand it, the tubes are essentially the same except for a
>slightly
>larger anode cooler which accounts for the additional dissipation. The
>parameters for
>typical operation on the 4CX1500B data sheet are based on a load line closer
>to class A
>than those on the 1000 sheet -- they call for lower bias and screen voltage
>and more
>idling current. The intention is to produce much less IMD. Since I'm a CW
>operator, I
>would rather have full legal output than reduce IMD.
REPLY:
Ok, but "typical operation" is just a starting point. Don't feel bound by that.
If you want max output and max gain, put the screen voltage close to max (400
VDC) and set the bias for a small amount of idle current, say 100 mA or less.
The higher the screen voltage, the higher the gain. The lower the idle current,
the higher the efficiency but the higher the IMD too. For CW, as you imply, IMD
doesn't matter.
One thing to be aware of when using swamped grid design: This tube has a fairly
high input capacitance in grounded cathode mode, aprox 80 pF. You will no doubt
have an SWR problem on the higher bands so you may have to switch in a parallel
resonant circuit to compensate. Or if your transceiver has a good antenna tuner,
or if you have an external one, that may take care of it. Just something to keep
in mind when you're doing the layout. Leave room for the parallel resonant
circuit and switch if you need it. Better yet, breadboard it first and check the
SWR with an MFJ SWR analyzer or the equivalent.
73, Bill W6WRT
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