"Richard Staples" wrote in
message

It has always been my understanding that vacuum tubes
actually generate noise when used in circuits and this
noise prevents tubes from achieving the same signal to
noise as a solid state or transistor circuit can achieve.

*everything* generates noise, its just a matter of how little or how much.

As a rule, transistors and ICs are quieter than tubes for audio, but in some
cases that's not a given.


I recall that during my early days in amateur radio
someone even developed a procedure whereby some of the
tube in the receiver circuit were converted to a solid
state tube to help reduce the noise inherent in tubes so
that extremely weak signals were not covered by not only
normal atmospheric noise but that PLUS the noise added by
the tube circuits.

There have been solid state devices that plug into tube sockets and perform
in a similar fashion. However, its not a given that they will perform
better. They are usually chosen for their longer life.

I asked a former NASA engineer about
tube noise and he dismissed this by saying that it was
not so much the tubes themselves but other noisy
components in the circuit like capacitors and resistors
and by carefully choosing the appropriate devices for the
circuit that today you can now design a very quiet tube
circuit.

It's always been possible to design tubed circuits that approach the noise
performance of solid state. It usually just costs more and you end up with
something that has other difficulties such as size, heat, and other
performance parameters.

For example, due to impedance matching considerations, an input transformer
is required to make a tubed mic preamp whose quietness approaches that of a
fairly inexpensive SS equivalent. Unfortunately, the transformer is costly
and causes other problems.