On Tue, 19 Apr 2005 20:22:10 -0400, Ken Scharf
wrote:

William E. Sabin wrote:
"Reg Edwards" wrote in message
...


To base conclusions on the greatly different working voltages and
currents of devices is entirely incorrect. But it is easily done and
leads to misunderstandings when novices and learners attempt to
analyse circuit operation.


It is not incorrect. It is quite correct, and everyone who designs
solid-state linear RF power amplifiers (including me, not a novice) knows
that it is correct. The truth in this matter is perfectly obvious to any
really knowledgeable individual.

Bill W0IYH


Are we confusing load impedance with the device equavalent (sic) resistance?

You may be confused, I am not. The OP wanted to know why solid-state
amps were push-pull without tuned matching networks while tube amps
are usually single-ended and have tuned matching networks. Bill and I
offered accurate explanations for this and Reg, as often happens,
wanted to inject comments designed to obfuscate the discussion.

Reg also opined, "Somebody said the internal resistance of
transistors, in general, was much lower than that of tubes. He was
incorrect." I believe that he was trying to put these words in my
mouth when of course, I didn't say that, nor did I see anyone else
saying that in this thread.

A vacuum tube amplifier operating at Ep = 4 KV, Ip = 500 mA and a 50
Ohm load impedance almost demands a tuned matching network.

An FET amplifier operating at Ed = 50V, Id = 40A is more readily
matched using broad-band transformers.

When comparing *one to the other* I contend that the vacuum tube
*amplifier* is a relatively high impedance device and the FET
*amplifier* is a relatively low impedance device.

As Bill already stated correctly, "The internal impedance of the
device is irrelevant."