On Sep 2, 2004, at 9:07 AM, Will Matney wrote:
Bill,
I was reading about this a while back. If I recall, the spacing
between the screen grid and the anode in power tetrodes help control
secondary emission reaching the screen from the anode. If you recall
the innards of a power tetrodes, the screen and control grid are in
precise alignment and are close together. But the anode is a good
distance beyond the screen. In pentodes or beam tetrodes (most which
still are called pentodes) of course, the suppressor grid or the beam
plates keep the secondary emission from reaching the screen being at
ground potential. I'm pretty sure I was reading this in either the
Care and Feeding texts by Eimac, or in the RCA Transmitting Tube
manual. One of the two spoke about this same thing.
This makes me wonder, why don't more if any amateur amps use power
pentodes?
Compared to tetrodes, pentodes are more difficult to manufacture, which
translates as more costly and their sockets are even more so. The
largest pentode made is the 5cx3000A. It costs a bunch more than a
4cx10,000D, it puts out only c. half as much suds, and, more
importantly, it does Not have handles.
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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