300b, x45, 211, etc.

Thanks Joe for the kind words, but in all modesty I rarely use my title even in a professional setting. It's too prentious.

For Joe,

The PX-25 is a pre WW-II power triode developed in Europe. Real PX25's used an odd B4 base rather than the more common UX4 base and could put out a bit more power than a 300B. The PX 25 is a bit more linear than the 300B and supposed to have better extension at the extremes. Real PX25's are rare and I have only seen them in Japan. KR started making 'PX25' a few years ago. This tube has curves that are like old PX25's but slightly different electrical ratings. The new PX25 has a lower maximum plate voltage and can be found in both b4 and UX4 basings. The only amp I have heard using the PX25 is the Art Audio PX25.

For Bio,

The main point in my message to Joe is that implementation is more important than the sound characteristics of a particular tube. The Mastersound 845 reference is the best 845 amp I have heard. It is even better with the right driver tubes and some mods. My friend who is a long time Mastersound dealer also runs his with a Hyperspace into JM Lab Utopias. Other 845 amps I have heard (Air Tight, Quadric, etc....) have not been so transparent. I am biased because compared to a 2A3 and 45, I do find the 845 a bit thick.

Even though I agree with Greg about the 300B in general, I have heard 300B amps that do not have those flaws. Try listening to a Shindo 300B limited.

One final point, I think the sensitiviy issue with SET are often overblown. For many types of music, 8 W into a 90dB speaker is fine. I ran a 2A3 for many years into a 92 dB speaker. Except for large orchestral, it was fine. Your own mileage may vary. Remember that it takes double the power to increase the sound pressure by 3 dB.

Bio-Yes, it is Taurus Audio in the bay area. You can usually find me there on Saturday or Sunday afternoons hanging out. That's why I have logged many hours with the Mastersound. I refer to Taurus Audio as the audio version of "Cheers".

The phonostage that Louis runs is the big Aesthetix. The stock tubes have been changed on the Mastersound as well as some of the stock parts. too bad the Euro is high against the dollar. When Louis first brought in the Mastersound it was $6 K. Of course, the Euro was trading at 1.23 Euros to the dollar then.

As to your other question, there is no set rule on speaker pairings and amp power. Obviously, a 2-3 W amp is not going to get you earthshaking sound unless you have really effficient speakers (94+ dB). However, for some applications it works well (small room, jazz, simple vocals, etc.) It's just that for a low power amp, you end up running at max power alot and possibly clipping which takes you into a higher distortion range on the amp.

I used to have a speaker which was 92 dB and never dipped below 8 ohms. It worked well enough with my 2A3 but the bass was always loose. That speaker just needed more power to control the bass. In another case, I heard a 10W amp driving a 90dB and 8 ohm speaker which had really tight bass and marvelous sound. You just have to find the right pairing.

Glassaud,

You bring up a good point that can be extended to many 300B amps. In my opinion, many commercial 300B amps use the wrong driver which leads to the problems Glassaud describes. These problems contribute to the general opinion about 300B's that were mentioned in post by Gregm. This is probably due to manufacturers having to use readily available tubes rather than rare and hard to obtain tubes. The 6SN7 driving a 300B is a common design but with common problems. In think the 2A3 and 45 are easier to drive so they don't have this problem.