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Best measuring tube amp

Probably few own or even pay attention to tube amps, and fewer have read technical reviews and measurements.

I do not know how they compare, but Atmas-sphere would be one I would check out. A modern OTL design with better performance and (far better) reliability than say Futterman amps. E.g. http://atma-sphere.com/en/ma-3.html

I would imagine Ralph @atmasphere or @SIY might have something to say on the subject...
 
Best measuring in what aspect(s) ?

Besides, tube amps are not about good measurements.
Also not about longevity and stability (tubes age)
They are conversation pieces / audio jewelry at best, and very nice looking indeed.
They are heavy in weight, consume lots of power, tubes are fragile and microphonic and generally they are designed to 'color' the sound in some way.
The latter can only be achieved by something that does not 'measure' well (in FR, distortion, output impedance) so good measurements and 'tube sound' do not go hand-in-hand.

Measurements of tube amps can still have value when one wants to separate the chaff from the corn.
 
Stereophile is a good place to check for measurements. I forget the valve amp concerned, but one stood out a couple of years back in the review index by actually having a solid state-esque low output impedance and I recall low enough distortion too - VERY rare indeed I think.

One I've owned in decades past and which had a good overall performance and regarded as a good-un in the 60's was my Radford STA25 from 1966. These are being beautifully re-made to better-than-original spec I gather by Radford Revival and do look very good indeed if the power is enough. Output impedance is held below 2 ohms I gather, but will still eq a typical speaker a little though.

No idea of bench performance, but E.A.R Yoshino did some good designs, albeit at silly-high prices in recent years to cater for the 'more expensive is better' mentality of the far eastern audiophile market. Tim knew his way around an output transformer and could design anything you wanted on the back of a cigarette packet (and I believe, often did for others...).
 
Interesting question though, as I assumed that the 'instrumentation amplifiers' built in to my old Tektronix 502a tube based scope would have been reasonably linear with wide range of gain settings and hopefully low distortion? I do wonder?

I wish I still had it, it was a wonderful if very large and heavy thing.
 
roog said:
Interesting question though, as I assumed that the 'instrumentation amplifiers' built in to my old Tektronix 502a tube based scope would have been reasonably linear with wide range of gain settings and hopefully low distortion? I do wonder?

I wish I still had it, it was a wonderful if very large and heavy thing.
Click to expand...

The biggest issue of tube amps is the output transformer and power (current).
They are designed to add 'tube goodness' and thus not about linearity.

instrumentation amps for scopes had a completely different goal.
Distortion was not a big issue as it needs to be substantial to become visible on a scope.
Easy to make a linear tube amp (for instrumentation) using a few tubes and overall feedback.
Not much output current is needed either nor to make this be 10MHz BW either.
 
Ilkless said:
Of course there is a lot of reason to - the aesthetics for one, rugged repairability and just appreciation for the engineering needed. Just like high-accuracy mechanical watch movements.
Click to expand...
Yes, of course, there is a lot of reason to. My comment was all about the topic "Best measuring tube amp".
It's possible there are people who don't like the sound of tube amps but want it for other reasons. :)
 
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I'll assume you mean power amp- for preamps, my own might be contenders.

Contemporary? No idea, nearly all of them are pretty mediocre. From the old school, Krohn-Hite, Mac, Luxman 3045, the RCA 50W tube manual amp, H-K Citation II, Quad.
 
Here's a (long) article about what it takes to get low distortion from a tube amp:

Ultra-low distortion valve hybrid amplifier - Valve Radio

This site is devoted to vintage electronics -- radios and audio amplifiers. It is not about restoring and collecting vintage items, but rather about modifying them in attempt to improve performance and bring it closer to modern standards.
www.valveradio.net www.valveradio.net
The author measured a SINAD of 86dB when running it just below clipping. He doesn't cite how much power he was getting, but I doubt it was more than a handful of watts.

His conclusion is worth a smile, "why bother with this tricky and relatively low power design? All in all, the answers to these questions are yet to be obtained..." It's an interesting read though.
 
I'm actually pretty interested in this topic. There's a local builder, Linear Tube Audio, that makes OTL headphone amps (among other components) and I'm hoping to swing by this weekend with my DAC and headphones and give this amp a listen:

www.lineartubeaudio.com

microZOTL MZ2 Headphone Amp / Preamp / 1-watt Speaker Amp by Linear Tube Audio

The second generation of the product that started LTA, the MZ2 remains the reference introduction to the unique ZOTL circuit.
www.lineartubeaudio.com www.lineartubeaudio.com

I've heard it before, but I want to really give it a good listen to see if it floats my boat. Owners rave about it and state it's the best of the SS and Tube attributes in one package. My curiosity is piqued. I've got a RME ADI2 DAC and the SS headphone amp section of this is great, but I suffer from fear that something out there is subjectively better sounding and I'm just not sure. I think giving this LTA amp a listen would be interesting.
 
gruefellow said:
Purely out of curiosity - what is the best measuring pure tube amplifier you know of?

Off the top of my head I think the Quicksilver Horn Mono's are a serious contender. See here: https://www.stereophile.com/content...n-mono-monoblock-power-amplifier-measurements

Interpret "best measuring" however you wish.
Click to expand...
McIntosh MC 3500. reviewed in Electronics World in the late 1960s. Measured THD under 0.1 % from 20-20kHz at full power, 350w.

McIntosh MC 275. My own unit measured under 0.1 % THD at 75 W, 20-20 kHz both channels driven when tested at one of Mac’s amplifier clinics in the 1970s.

Luxman 3045. Tested in the 1970s.

Marantz 9 and 8B also met the under 0.1% THD 20-20kHz at rated output ppower benchmark.

The EAR 509 also has very low distortion based on tests. Around 0.1% THD at full power. It is probably the only currently produced valve amp that is is the same class as the old Lux or Marantz or McIntosh amps.
 
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skhan007 said:
I'm actually pretty interested in this topic. There's a local builder, Linear Tube Audio, that makes OTL headphone amps (among other components) and I'm hoping to swing by this weekend with my DAC and headphones and give this amp a listen:

www.lineartubeaudio.com

microZOTL MZ2 Headphone Amp / Preamp / 1-watt Speaker Amp by Linear Tube Audio

The second generation of the product that started LTA, the MZ2 remains the reference introduction to the unique ZOTL circuit.
www.lineartubeaudio.com www.lineartubeaudio.com

I've heard it before, but I want to really give it a good listen to see if it floats my boat. Owners rave about it and state it's the best of the SS and Tube attributes in one package. My curiosity is piqued. I've got a RME ADI2 DAC and the SS headphone amp section of this is great, but I suffer from fear that something out there is subjectively better sounding and I'm just not sure. I think giving this LTA amp a listen would be interesting.
Click to expand...
The measurements for LTA are a mixed bag. Some very odd distortion patterns. Very innovative design, though.
 
My view is that for well measuring valve amplifiers, one has to look at vintage amps, of the late 1950s and early 1960s. Radford and Quad in the UK were pre-eminent.

Any modern valve amplifiers almost by definition won't measure well, as their raison-d'etre is their perceived subjective quality (not forgetting looks), not their technical performance. Those famous amps of the past did their very best to achieve SOTA measurements for their time, and that was reflected in their cost, size and weight.

Now, it's all about cool looks and expensive looking materials, not technical performance. Transformers especially are nowhere near as good as they used to be both due to costs, and that the skills in design have largely been lost. Arthur Radford especially was a wizard with transformers, and the circuit design around the phase-splitter which resulted in much lower phase shift allowing a lot more feedback than was common in those days, or today for that matter, especially as these days feedback is considered a bad thing.

S.
 
DSJR said:
Stereophile is a good place to check for measurements. I forget the valve amp concerned, but one stood out a couple of years back in the review index by actually having a solid state-esque low output impedance and I recall low enough distortion too - VERY rare indeed I think.

One I've owned in decades past and which had a good overall performance and regarded as a good-un in the 60's was my Radford STA25 from 1966. These are being beautifully re-made to better-than-original spec I gather by Radford Revival and do look very good indeed if the power is enough. Output impedance is held below 2 ohms I gather, but will still eq a typical speaker a little though.

No idea of bench performance, but E.A.R Yoshino did some good designs, albeit at silly-high prices in recent years to cater for the 'more expensive is better' mentality of the far eastern audiophile market. Tim knew his way around an output transformer and could design anything you wanted on the back of a cigarette packet (and I believe, often did for others...).
Click to expand...
I have the schematics for the WAD 300b DIY on my desktop and occasionally think about building it, which would likely require custom iron and a true hair shirt experience. I can't imagine it would objectively improve on a Williamson or quad though, bar the power increase.
 
I don't really know but yes, McIntosh have ALWAYS been known for good sound. I'd expect the noise to be inaudible and the distortion and frequency response should be better than human hearing. They should be as good as any solid state amp.

But IMO - It's silly to buy something made with technology that's been outdated for at least 50 years. It's expensive, especially if you want power (Watts), it's very energy inefficient, and the tubes age, their characteristics change*, and they eventually die.

Transistors and MOSFETs are "naturally" low impedance which makes them more suited for driving 4 or 8-Ohm speakers, and that means they can drive the speakers directly without an output transformer. (An audio transformer doesn't necessarily degrade sound, but it's "difficult" to make a transformer that covers the full 20-20kHz range, and even more difficult and more expensive if it has to handle power without distortion.)

Back in the tube days, most audio equipment wasn't that great. It was never cheap or easy to get good sound, especially from a power amp (or a power-output stage) since that requires a transformer. With solid state it's been pretty easy from the beginning, and it's just been getting cheaper and easier with integrated circuits.



...Guitar amplifiers may be an exception. Guitar amplifiers are not meant to be high fidelity, the tube circuitry and the output transformer are designed to distort in a "pleasing way", especially when overdriven. Electric guitar doesn't sound right when played through a hi-fi amplifier. This makes the amplifier "part of the instrument". It also means that they all sound different and every guitar player has their favorite amp as well as their favorite guitar. Of course there are also solid state guitar amps, and they are also not high-fidelity. And, there are some that can "model" a variety of other famous amps.


* A GOOD amplifier CAN be built so that as long as the tubes remain in-spec the sound won't deteriorate or change. I'm sure McIntosh amps are built this way. Although transistors & MOSFETs don't age, their characteristics (such as gain) varies from part-to-part. So solid stage amps are usually built with the same philosophy.... So every amplifier off the production line performs consistently even though the parts vary.
 
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