Once you go 300b it’s hard to go back?

Hi Jond,

Personally for my taste if I ever went the SET route again, it's been some years, I would go for either the 2A3 or 45 tube over the 300B. Both to me are a touch more incisive and transparent though also lower power.

I used to be of the same opinion.  The thing about directly heated triodes is that you're basically hearing the driver tube, and the higher the power rating of the output tube, the more difficult it is to drive.  This is one reason for there being so many mediocre sounding 845 and GM70 amps.

The whole "Direct Heating" (Sakuma) movement in Japan was based on paying attention to the driver circuit, and they drove their high power triodes with output tubes ... sometimes, even pentodes!

The first prototype of our NiWatt amplifier had that typical lush but slow 300B sound.  As we paid more and more attention to the power supplies (4 of them per channel) in order to free up the driver circuit from the output tube's demands, the amp began to take on a "45 on steroids" characteristic - quick, delicate, articulate while harmonically rich but with power to spare.

Back in the'90's, this lush presentation worked for a lot of us because many high efficiency speaker systems could be a bit on the "rude" sounding side.  Now that we're seeing more and more refined high efficiency speaker systems, we don't "need" these colorations to serve as a tone control.  Some may like it, and that's ok too ;-)

Cheers,
Thom @ Galibier Design

Hi @jond,

Until I lived with Lynn Olson’s personal Karna amplifiers (http://www.nutshellhifi.com/triode2.html) while he was getting settled into his new house here in Colorado in 2005, much of this lush vs. quick 300B stereotype was theory. Yes, I’d heard 300B amps that were more or less incisive, but they still fell within a range that I’d refer to as a "normal" characterization of a 300B.

The material on Lynn's page is a bit dated, as the Ariel speakers are about to receive an upgrade to a horn system he's been designing over the past few years, but the basic amplifier design principles hold true to this day.

Of course, Lynn’s amplifiers are push-pull 300Bs (so this isn’t an apples to apples comparison with anything else), but he used all of the power supply tricks I’m using, and of equal importance is that his driver tube is a 45 (Sakuma/direct heating again - output tube driving output tube).

The Karnas' sound more like powerful single ended amps than push-pull, which plays into my theory that the better various architectures are designed and implemented, the more convergence there is between them.

Cheers,
Thom @ Galibier Design

Lynn is a brilliant theoretician and I feel fortunate to live in the same town - bouncing ideas back and forth with him. Having his Karnas in my house for those three months was revelatory.

Check out his essay "Illusion Engines". Some of it (written in the mid-90’s) is a bit dated, but the concepts are still viable (to me): http://www.nutshellhifi.com/library/illusion-engines.html.  He's primarily a "speaker guy" (having designed first for Audionics in the '70's), but he digs into all areas of audio with passion.

Cheers,
Thom @ Galibier Design