Triode vs. Pentode

Zaikesman- The best post I have ever read on the subject. Like my Atmas or my Cary; emotion and truth. Sciencist and philosopher. I am humbled. I have no idea if the technical details are correct, but I understood! Kind of like a triode tube amp.

Trelja: I agree that triode is preferable - and also think that higher power is preferable, all else being equal. That's the essence of what I try to analyze above: It's not triode vs. tetrode or pentode - to me triode wins that contest. It's triode vs. higher power obtainable from the same amp. In that there can be some tradeoffs, but as always depending upon many other variables.

As you indicate, the benefit of the extra power from tetrode or pentode is not mainly about higher volume for the same preamp setting. My Levinson preamp's volume control is calibrated in tenths of decibels, and switching modes seems to require only about a 2.5dB adjustment in order to maintain a matched level (but I can only go from triode to tetrode, not pentode).

"Triode injected into the midbass that extra muscle (not plumpness or lack of control)..."

I too have heard the fuller quality in the bass and lower mids you talk about with triode. Sometimes things can sound a little lean in tetrode. However, I do think that this can be explained with the model I describe above. Two characteristics combine to produce the effect. One is that tetrode or pentode is going to sound brighter, due to the different harmonic emphasis. The other is that triode is going to let the woofer have its way a little bit more. Whether the overall result sounds more accurate or not will depend on the speakers and room, the rest of the system, the program material, and I'm sure the listener.

Although I cannot agree with the theory that there could literally be "extra muscle" behind the lower frequencies with the lower-powered mode - and in fact I believe it was in large measure precisely the sound of less muscle that you heard - I can see the possibility that different modes of operation might not only have different harmonic structures and different power outputs, but maybe also different tonal balance tendencies. But it's hard to know this for sure, separately from the twin factors of harmonic structure and output power, because both of those properties can affect our perceptions of tonal balance.

"Although the volume measured the same, subjectively, listeners swore it was a good bit louder."

Why triode would sound more dynamic is harder to intuit, but the above comment is revealing. Often a little compression actually makes the music sound 'fatter' and subjectively 'louder' if we tend to calibrate our volume-match to the peak levels. This can be an enjoyable effect. Higher dynamic contrast can actually sound 'quieter' at the nonimal average level. Impulses that are slightly compressed in amplitude, get spread out slightly in time as a result. The ear can perceive the extra overhang as being 'more', whereas the tautness of the uncompressed peak, leaving little trace in the time domain, can actually sound like 'less'. Or maybe in certain situations, just backing off a little on a preamp's volume control in order to match levels for tetrode or pentode causes a slight dimunition in the perceived dynamics. It's tough to isolate all the variables. Just better to listen and enjoy.

Another great post, Zaikesman.

One thing that I have long considered when people say "volume", is that we normally measure this in a more static manner than may well be necessary. Rather, I am saying, these SPL meters are probably taking a snapshot of the volume, with perhaps one frequency weighing most heavily. This might be fine for a test tone.

But, as I ALWAYS say, measurements often continue to have little correlation with music or sonics because both are dynamic. I don't listen to, nor do I have a desire, a 1KHz tone going through an 8 ohm resistor(does it even make a sound?), and I would guess most audiophiles don't either. We listen to music; dynamic, unpredictable, ever changing.

Also, one thing I want to point out is that the Granites, running KT88s in triode into the Coincidents are definitely not near the clipping, or even compression point. It is a pretty benign load there.

No, triode definitely has more of the blood and guts of the music playing in my particular setup. This might be something apparent in my system, and the opposite in other people's. But, it is giving me further insight into what a lot of people talk about when they speak of their SET amps.

Over the past few months, I have been looking into a lot of things in my own systems, and am finding my opinions are flying in the face of conventional wisdom. Hopefully, in these threads I will be able to share them as time goes forward. I am certain that many things I will say will spark a tremendous amount of controversy, but nevertheless, this is what I am hearing.

Trelja...Because music is "dynamic, unpredictable, ever changing" it makes a lousy tool for testing. Results with simple signals like a 1KHz sine wave, or a square wave, or whatever, are repeatable and therefore useful to reveal the effect of various design changes that one might make. The test signals can also be correllated with particular amplifier characteristics that you think are important. Of course the ultimate test is how it sounds with music, but you would never get to a sound that you would like without a lot of work with test signals.

That's why they make vanilla AND chocolate!

Some people are more concerned with test tones, some prefer music - to each, his own...