John Fielding wrote --
>>What's the difference?
>
Carl Heuther, KM1H, wrote --
>The 250R has a minute (Eimacs word) .2pf increase in output C over the
>7580. Both have a higher perveance than the 250B and require a slightly
>more negative bias voltage.
>At 1500V Ep any version can be made moderately clean. At 2000V they are
>horribly dirty.
? Carl: . By looking at any of the constant-current curves, one can
see that the closer the instantaneous anode/plate voltage comes to the
screen's supply.V, the greater the departure from ideal straight-line
linearity. On Eimac's constant-current curves for a screen potential
of 400v for the 7580]4cx250R, the curve for 1.2a is quite flat between
2000v and 600v. Thus, with a supply potential of 2000v, 1400v of rather
linear movement in the instantaneous anode potential is possible.
However, if a 1500v supply were used, only 900v of linear movement in
instantaneous is possible, and the most linear part of the curve
between1500v to 2000v is lopped off. How could eliminating the most
linear part of the curve make the tube "horribly dirty"?
- cheers, Carl
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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