Triodes and Tetrodes and SET, Oh My!

Ron Resnick · Aug 6, 2016

Most low-power SET amplifiers use single-ended triode tubes. But some, like the N.A.T. Audio Transmitter and Magma amplifiers, use single-ended tetrode tubes.

Then, we have some of the push-pull VTL amplifiers which are switchable between triode mode and tetrode mode.

So what is the story here?

If we rank the sound of these circuit topologies on a spectrum which is "sweet, liquid, warm midrange" on the left side (low-power, single-ended triode), and "more neutral, more punchy, less warm" on the right side (push-pull tetrode) where do single-ended tetrode and push-pull triode fall on the spectrum?

Can we assume that a single-ended tetrode from N.A.T. is going to sound more single-ended triode-like than a push-pull VTL in triode mode? Or not?

What is your experience comparing the sound of these different circuit designs?

Zero000 · Aug 6, 2016

Without a constant reference i.e. the same speakers, it is hard to make solid judgements.

I have heard the older 211 based NATs and the Transmitter (both on the AA Omega) and Magma but on incomparable speakers.

I have also heard many of Audio Note's single ended designs, since I know someone who is an AN devotee. Here's some thoughts on one of the AN single ended amps I actually seriously liked: http://theartofsound.net/forum/showthread.php?45110-The-211s-Have-Landed-And-Taken-Off-Again!!!. Better than the Kegon balanced I think and by a margin. The Kegon Balanced is about £70K so not cheap, and was review by Kevin in Hi-Fi Critic recently i.e. the chap I know and visit.

What was interesting here was how this single ended Tomei shared so many traits that were similar to my push pull 211s in the same system. So you kind of wonder what difference single ended versus push pull really makes for really good single ended implementations. My own amps had a massive power advantage, though I would say the Tomei was "probably" superior within its power constraints. With the wick turned right up, though, no way could the Tomei compete.

The Kegon, Kegon Balanced, Kageki and P4 monos all sound quite different from one another, in a way that you cannot attribute the fact that they are single ended as being the reason for them sounding the way they do. Though I will say the Kageki was my least fave with an 8 Watt output. Not enough even for AN/Es.

The NATs sound great in 211 and Transmitter form on the Omegas.

Al M. · Aug 6, 2016

Ron,

I have a low-powered push-pull triode amp, playing on sensitive monitors, thus an easy load.

Tonal balance is neutral. I had a Spectral DMC-15 SS/DMA-260 pre/power combo in my system (on my old speakers) and tonal balance was very similar; Spectral has the reputation of being very neutral.

When tube amps are on a heavier speaker load they may sound more warm, muddy and sirupy. But that will also depend on the power supply. I have large external power supplies (see my system thread in signature) and these always deliver enough power to the amps without ever sagging in complex passages. Basically the amp will never clip until max. output, which is not typical of tube amps. In extension, the amp will also be able to handle a somewhat heavier speaker load well, compared to a similar amp but with less beefy power supply.

So the answer to your question will also depend on how good the power supply of the amp is, and how heavy the speaker load. It will be hard to make a generalization.

Jeffy · Aug 6, 2016

I beg to differ as I feel that there is no tube amp out there that can give me the current I need to drive my Rockport Altair's. They are mostly a 2 ohm load and this my friend is where you need a high current solid state amp.

Al M. · Aug 6, 2016

Jeffy said:
I beg to differ as I feel that there is no tube amp out there that can give me the current I need to drive my Rockport Altair's. They are mostly a 2 ohm load and this my friend is where you need a high current solid state amp.

Jeffy, I am not aware of anyone here claiming that tube amps can handle any speaker load. Low impedance loads tend to be a no no indeed.

What kind of amps do you have? The low impedance of the Rockport Altairs may explain why the sound that I heard with them was mediocre. The sound was strained with the large SS monoblocks that drove them and which did not seem up to the task. I bet they are much better speakers than what one might conclude from the sound they produced that day.

cjfrbw · Aug 7, 2016

Hard core tube guys will also make distinctions based on directly heated filaments and indirectly heated filaments. Further parsing can be made in directly heated filaments between AC and DC, AC being more noisy but reputedly better sounding. Some guys will also make distinctions between the filament voltages, lower voltages giving a finer, more evanescent sound, and higher voltage filaments giving more robust, meaty sound.

A lot depends on implementation and transformer quality, of course, but I tend to find that the midrange and upper midrange of directly heated single ended triodes are more fluid and open sounding than in push pull. Indirectly heated tetrodes and pentodes in push pull are a bit worse, and never quite seem to give that wonderful quality of midrange fluidity and can sound compressed in the upper midrange.

That being said, I have heard some well implemented push pull tetrodes that sound awfully good.

bonzo75 · Aug 7, 2016

NAT will be able to drive Rockport, stable to 2 ohm loads and the UK distro prefers to use Jadis for his own personal Altair system.

Ron Resnick · Aug 7, 2016

I heard Altair IIs driven by a BAT amplifier (courtesy of Ken Boyce of Cake Audio in Southern, California) and I thought the system sounded great.

I also heard Arrakis driven by VTL Siegfrieds and I thought the system sounded completely amazing. And there is a fellow in Texas with Arrakis who, I believe, also uses VTLs.

As always, people have different preferences.

Al M. · Aug 7, 2016

cjfrbw said:
A lot depends on implementation and transformer quality, of course, but I tend to find that the midrange and upper midrange of directly heated single ended triodes are more fluid and open sounding than in push pull. Indirectly heated tetrodes and pentodes in push pull are a bit worse, and never quite seem to give that wonderful quality of midrange fluidity and can sound compressed in the upper midrange.

I have heard CAT JL7 amps with wonderful midrange fluidity and openness in the upper midrange. They use KT150 tubes that are indirectly heated pentodes. Again, I don't think that generalizations can be easily made.

Ron Resnick · Aug 7, 2016

I knew this was going to be a complicated thread!

I was hoping one or more members might have directly compared N.A.T. single-ended tetrode to VTL push-pull triode mode on a familiar system.

Of course, to make it more complicated, different tubes sound different, even separate from the different circuit types.

Ron Resnick · Aug 7, 2016

User211 said:
Without a constant reference i.e. the same speakers, it is hard to make solid judgements.

I have heard the older 211 based NATs and the Transmitter (both on the AA Omega) and Magma but on incomparable speakers.

. . .

The NATs sound great in 211 and Transmitter form on the Omegas.

Do you have any other impressions of the Magmas you can tell us about?

How would you compare on the AA Omegas the N.A.T. 211 versus the N.A.T. Transmitter?

microstrip · Aug 7, 2016

Ron Resnick said:
I knew this was going to be a complicated thread!

I was hoping one or more members might have directly compared N.A.T. single-ended tetrode to VTL push-pull triode mode on a familiar system.

Of course, to make it more complicated, different tubes sound different, even separate from the different circuit types.

To make it even more complicated - I have owned the MB750's for long years and a neighbor of mine has the Siegfried II - I can assure you they sound really different. IMHO what we listen with the new VTL's can not be compared directly with our experiences with the MB750.

Brucemck2 · Aug 7, 2016

microstrip said:
To make it even more complicated - I have owned the MB750's for long years and a neighbor of mine has the Siegfried II - I can assure you they sound really different. IMHO what we listen with the new VTL's can not be compared directly with our experiences with the MB750.

Please elaborate; what are the relative merit of the Siegfried II vs MB750s?

I used to own the MB750s, and with big Genesis ribbons they were magical in triode mode.

Ron Resnick · Aug 7, 2016

Brucemck2 said:
. . .

I used to own the MB750s, and with big Genesis ribbons they were magical in triode mode.

I use only the triode mode on my MB-750s on the Martin-Logans.

Did you ever try, or were you ever tempted to try, single-ended triode amps to drive the ribbon panels on the Genesis?

marty · Aug 7, 2016

Ron,
I owned VTL Siegfried's for many years and did the triode/pentode experiment many times with my Pipedreams. In short, I always preferred the Triode mode. But remember I was only running the Towers and let my JL subs do the bass from 80Hz down. That said, triode mode offers a more refined, musical sound with better sound staging resolution and instrument timbres. I would recommend using the Pentode mode if you really need gargantuan power, but for most applications, I would favor the triode mode. Of course, the beauty of this great product is that you can decide what works best in your application with the push of a button!
Marty

bonzo75 · Aug 7, 2016

microstrip said:
To make it even more complicated - I have owned the MB750's for long years and a neighbor of mine has the Siegfried II - I can assure you they sound really different. IMHO what we listen with the new VTL's can not be compared directly with our experiences with the MB750.

What speakers and TT does your neighbor have

Ron Resnick · Aug 7, 2016

I agree! Thank you for reporting, Marty!

Did you ever try, or were you ever tempted to try, single-ended triode amps to drive the Towers on the Pipedreams?

Zero000 · Aug 7, 2016

Ron Resnick said:
Do you have any other impressions of the Magmas you can tell us about?

How would you compare on the AA Omegas the N.A.T. 211 versus the N.A.T. Transmitter?

Just way too much time between the 211 versus the Transmitter to comment accurately. The Magmas were on a completely different system playing classical at low levels. So comments meaningless, really.

Just being honest.

Brucemck2 · Aug 7, 2016

Ron Resnick said:
I use only the triode mode on my MB-750s on the Martin-Logans.

Did you ever try, or were you ever tempted to try, single-ended triode amps to drive the ribbon panels on the Genesis?

At various times had a BEL solid state, BAT75 SE monoblocks, MB-750s, AR Ref 110, and for awhile Viva Aurora (but I could not get rid of a microphonic/grounding issue on those so I never really got to hear them at their best). The MB amps in triode mode were my favorite.

microstrip · Aug 7, 2016

Brucemck2 said:
Please elaborate; what are the relative merit of the Siegfried II vs MB750s?

I used to own the MB750s, and with big Genesis ribbons they were magical in triode mode.

Compared to the Siegfried II the MB750s sound "slow", mainly because of their bass. Also although transients sound great when playing loud, they do not have the same capability in whispering passages, as some more modern amplifiers do. The MB750s were great on instrumental music, IMHO not comparable in vocals.

I have owned and loved the MB750s for many long years, but IMHO their sound is now dated. It is like comparing an Audio Research D70 versus the REF150, or the old cj premier 8's with the LP275m's. It is not a question of just bass, midrange or treble, dynamics or microdynamics - it is the overall sound quality.

Triodes and Tetrodes and SET, Oh My!

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