>Some tubes can have the grids driven positive without measurable
>grid current. I tried to explain that difference earlier. ..
A representative tube type would seem to be appropriate to illustrate the
point.
>The thing
>that affects cathode to anode resistance is the ELECTRIC field
>between the grid wires, not current flowing in the grid. In tubes
>like the 8877 and 3CX800, Eimac puts the cathode material on in
>bands. If you look at the cathode, the grid wires are NOT between the
>cathode's emitting area and the anode.
>
>That's why 8877's and 3CX800's have very low grid current even
>when a portion of the RF cycle drives the grid very positive with
>respect to the cathode.
With a grid to cathode voltage of 67v, an 8877's grid current is about
600mA. (Eimac Curve #4250)
Rich---
R. L. Measures, 805-386-3734, AG6K
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|