On Tue, 4 May 2010 14:31:11 -0500, "Tim Williams"
wrote:

"John Larkin" wrote in message
.. .
Gm/Co was a popular figure of merit for tubes used in video amps and
oscilloscopes. They took a hockey-stick turn upward when frame-grid
tubes were invented, just before semiconductors took over.

7KY6 has four times the transconductance of 2N3819, and plenty more voltage
and power capacity.

Tim

Sure, but a 3819 is a dog. Jfets are wimpy, although a BF862 has a bit
more Gm than the 7KY6.

For serious transconductance, phemts and GaN fets are the winners,
with whole digits of siemens to the left of the decimal and absurdly
low capacitances.

John