Robert Casey wrote:






12AU7 are still reasonably plentiful as NOS items, since they have
become unpopular amoungst hi-end users, imho.



Unpopular as they should be !! It's a dull sounding tube and looks like
sh*t next to a 300B or other power tube .


What does it matter what the tube physically looks like? It's a 9 pin
twin triode and looks similar to a 12AX7. Depending on the
circuit, they could sound great. In my equipment the tubes are partially
hidden from view.

The 12AU7 comes in various forms, both large plates,
and some with very small plates.

One simply has to *try a few samples* before deciding if you like any you
have
tried.

The same applies to most other tubes, and to come to some general
oppinion that all 12AU7 suck is to oppine negatively without sufficient
basis.
The big plate versions are very similar to big plate versions of 6CG7, some
of which
have long plates identical in everyway to those used in some 6SN7, and the
12BH7.
It seems to me that the only thing that is different is the grid wire size,
wire spacing,
and size. I bet the cathodes are fairly similar.
The 12AU7 is simply a generic low U signal triode like so many others,
and thus possibly conveys the best of audio like any of the rest, depending
how
discerning you are.

The 6SN7 is a better looking tube alongside a 300B, but not alongside
a 417 or EL84. An ECC33 or 32 might look better with 300B.
One bloke I know prefers a choke loaded 2A3 to drive a 300B.
Whatever is used will sound a little different, and then what of the
differences that
may exist between channels? Pity the guy with a tubed HT system,
it'd be unlikely he'd have 5.1 sweet sounding channels unless he was
extremely choosy.
Does one really sugary channel with a sour channel add to be a mildly sweet
system?

One has to choose preamp and other tubes carefully, especially those without
loops of NFB,
although one could say the NFB sours sweet sound as much as it sweetens sour
sound.

Tubes allow us freedom to explore colour, without straying from
what is technically hi-fi.

I remember people in the 1970's having similar discussions about the
types of transistors they used.

I won't go there, I'd prefer to use fets.

Patrick Turner.