"Murray" wrote in message
...
It should be remembered that FETs are a voltage controlled
current device. A tube is a voltage controlled voltage device.

A tube is also a voltage controlled current device because of its
transconductance (gm) as well as a voltage controlled voltage device because
if its amplification factor (mu).

A FET can be thought of in the same way if the gate is not forward biased.
MOSFETs are even more closely related. The difference involves the way that
the device is used. In some transistor circuits the "topologies" are amost
identical to tube circuits.

FETs almost always operate at lower B+ voltage than tubes, so drain voltage
max-to-min swings are smaller and drain current max-to-min swings are
greater, which suggests lower values of drain load resistance.

Fifty years ago I designed pulse amplifiers at work (GE)for nuclear event
detectors using the 6CW4.

At one time special low plate-voltage (12.6V) tubes were made for car radios
in order to eliminate the high voltage power supply that used either
vibrators or the 0Z4 tube.

Bill W0IYH