SET vs OTL

Paul, I like the type 45 tube a lot too. Not many speakers that will work with a 45 SET though. I am using a set of Coral Betas, which are fine as long as you don't expect any volume.

Larryi, We've been doing this over 30 years now and all our amps have had a direct coupled output. We've seen many tubes fail in that time. So far, we can still count the number of times that a power tube failure damaged a driver on one hand. In all the cases but one, alternative power tubes had been installed in the amp. So it appears that the amp is quite safe. All of our amps except the big 500-watt unit do not use a servo circuit (we installed one in the big amp, but for convenience only). They are quite stable, and simply don't need a servo. The key is controlling the power tubes, something that you would **think** would be common sense, but it is an issue in a lot of designs. That is one of the reasons why our amps have been so reliable over the years (the other being that the amp does not need negative feedback to work).

Martykl:

Gotta side with Paul on this one. My Wyetech Sapphire monoblocks use two 300Bs in parallel per side (18 wpc) and sound exactly like Paul describes: "crystal-clear, just right, completely natural", and certainly not lush. And these are 300Bs! And they drive monitors with a wild impedance swing as well.

Agree with Paul. The 45 is the triode gold standard.

Followed closely by 50, 2A3, and PX-25.

The 300B is a distant fourth and IMO, highly overrated.

I agree with Bill's ordering of the triodes except that I've never heard a 50.

300B can be done well (I learned recently I really like the JE Labs 76/6SN7/300B circuit) but bad implementations outnumber the good, it seems! The thickened midbass and blunted transients is a show-stopping for me.

I'd also throw the PX-4 in there either before or after the the -25. I had a Kurashima PX-4 - amazing amp.

People always talk about how much difference the circuit, driver, power supply, and output tranny make, yes the various tubes almost always retain their basic sonic character no matter what the amp IME.

However, I've heard those Wyetechs really break the 300B mold. I've also heard that about the Welborne DRD circuit.

As for volume and dynamics, yes, for a 45, you need a back horn, front horn setup, or highly efficient widebander on OB. But it's amazing how dynamic the good SETs are within their capabilities.

Any decent 300B SET will drive 90 dB/W dynamic speakers that are a fairly easy load very well. I'm thinking DeVore, Green Mountain.. lots of others.

Its the amp design,construction as much as the output tube thats responcible for sound quality. Having owned over 10 -45 SET. Probly arround 25 others SET many OTL SS PP etc. I can say that I did not find 45-50 SET to be the best in anyway. I look at total design not just tubes used and make dam sure it matchs loudspeakers or you SET yourself up for falure which is what most 45 2a3 owners do. Wavac, MasterSound, PAD, John Hogan have owned these 300b amps and they sounded much better than my 45 SETs and I have owned most of the great 45 SET amps that get raved about. With SET match your loudspeakers to amp or forget about it. Would say the same about OTL designs.