>On Fri, 18 Dec 1998 10:54:06 -0800 Rich Measures <email@example.com>
>>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.
>>Ä 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
>>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
>Since you believe what is published Rich ( when it is convenient ) how
>come you cant agree with published Eimac results?
? Eimac said that linearity improved when the anode supply voltage was
decreased from 2000v to 1500v?
>I also tend to disbelieve claims that I can not verify with HP quality
>test equipment. You make a lot of claims that I can not verify here with
>a similar amp.
>The consensus from several continents appears to agree that the
>7580/4CX250R is dirty at higher Ep. Why do you always want to play word
>games and ignore some basic facts supported by measurements?
? When alleged measurements do not agree with what one sees on the
constant-current curves, my guess it is that problem is not in Eimac's
- Have you tested a 4cx250R with 400v on the screen and 2000v on the
>Please, dont repeat the old canned drivel...try something new for a
>change. You are beginning to sound like ur old buddy ...
? If you are speaking about Mr. Rauch, he seemed to get moderately
perturbed by the information I obtained from Eimac's constant-current
curves when he was trying to convince us that high-Mu triodes could be
successfully operated as linear amplifiers in Class AB1/grid-driven
- later, Carl
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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