Here's a great offline response I got from Dr. Chau that I'm posting with permission:
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First, you have to realize there are no absolute rules to the sound of a
particular tube. The end result does depend on implementation. However,
you can breakdown trends in two ways. Each family of tubes does have a
commonly accepted 'sound'. Also, many SET manufacturers have a house sound
including Cary.
300B: the most recognized SET tube. Often said to have a rich, warm and
glorious midrange. Also often said to be a bit rolled off on the top and a
bit loose in the bass. Still, it's reputation is from the glorious
midrange. The first popular directly heated tube in the US (had been
popular in Asia and Europe for much longer).
2A3: similar to the 300B but much less power (typically 3W). A bit cleaner
in the mids, more top end, and much better in the bass. The bass from a
2A3 is really good depsite the low power. This became popular in the US in
the late nineties since it was cheaper than the 300B and considered to be
cleaner sounding than the 300B. FYI-I currently use a 2A3 at home although
that will change in a week or so.
45: an even older tube than the 2A3 or 300B and even less power (2W). This
is the current hot tube in SET. Considered even more transparent than the
2A3. Supposed to be better in every way than the 2A3.
The above tubes are directly heated triodes but use an oxide cathode like
most small signal tubes. The next group of tubes are transmitting tubes
and use a thoriated tungsten heater/cathode
211: a popular transmitting tube. Can put out 12-15 W on a single tube.
I've only listened to a 211 on several occasions. I find it a bit thicker
sounding than the 2A3 and 45, more like a 300B.
845: the current hot high power SET tube. can go up to about 18 W on a
single tube. I find it somewhat less transparent than the 211. Many
commercial amps are available with this tube now.
The bass on the 211 and 845 is probably a bit bigger than the 45,2A3, or
300B but not as quick.
Other tubes:
212, 807, 811, 833A-other transmitting tubes. Some are really large like
the 212 and 833A. These can put out a lot of power (100W for a 833A) but
can be dangerous as they need very high voltages on the plate to achieve
max power. The 811 and 807 are smaller and in between the 845/211 family
and the 45/2A3/300B family.
10, 101D, VT52, etc. other small triodes in the vein of the 45. These
often are considered even better than the 45 but have really low output and
are rare. Very few commercial designs are available.
The above comments are gross generalizations and based on my own
experiences. Again, a good design can change the characteristics. A
current thread in the forums is to run the 845 at much lower than normal
voltages (i.e. lower power) which changes the sound.
Also the above tubes are all triodes. One can get good single ended sound
from pentodes and tetrodes. I just purchased a Shindo Cortese to replace
my 2A3 amps. These run a F2a pentode.
In addition to a specific tube sound, manufacturers have a characteristic
sound. Cary certainly has a family sound. Even though the first SET I
heard was a Cary and I used to own a Cary, I'm not a fan of their sound.
As to you question about moving to another tube, you will can find big a
difference even if you move to another manufacturer's 300B amp. It all
depends on what you want in terms of sound. For SET amps, I think you have
to consider the amp and speaker as one unit. This is especially true for
the lower power tubes. If you can, try to listen to a 2A3 or 45 amp since
I think you'll hear the biggest difference in these tube tubes compared to
a 300B. You can only answer you question by listening.
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