I am completely in the dark... Who's pushing the envelope in tube designs and in what ways? What are, say, the differences between a CJ, ARC, a VTL and a Lamm? Other than self-biasing, what are some key innovations in the area the last 10 years???
Are tube designs still evolving, or have all circuits effectively been invented?
- Thread starter ack
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I really don't know since I am not a circuit guy. What I have noticed is that compared to say a Dynaco or Eico, today's power supplies are pretty complex affairs for both preamps and amps. I think this is the area where there is greatest evolution.
I would agree but extend this a bit. I own a 2 box line stage with separate power supply; each box weighing ~90-100#. The unit uses mercury rectifier and DHT design with 71A tubes. The basic design dates back to the 1930's and uses 60+ year old tubes. Improvements in materials, circuit layout, etc. allow the designer to create a state of the art design based on mature technology.
The matching two box phono preamplifier that uses an LCR (inductor, resistor, capacitor) low impedance design that allows high signal transfer compared to the typical R/C RIAA correction. My understanding is that the concept was developed some 40 years ago, but cost and difficulty of implementation make this an unusual design. The power supply and signal boxes each weigh 90-100#...
Tubed gear requires a hefty power supply to reach its potential and typically this is often what is sacrificed when building to a price point.
I am no techie. My only comment would be that tubed tech has been around so long, i think the improvements are at least partially in: superior materials, higher consumer budgets for all-out execution, and in general as tech moves on, superior execution on the production of tubed equipment (teflon capacitors, using higher quality wiring, beefier power supplies, etc). I am sure certain designers are doing things today that no one did 5-, 10-, 20- yrs ago...but i am not sure it is always because no one had thought of it...tube circuits have been around for decades...i suspect in some cases, it was budget driven. Aside from the CJ ART, how many $30,000 preamps were around 20 years ago? Today, preamps run into the 6-figures.
In terms of what i hear, my observations on tubed gear (in general but also based on my 12-years of owning 3 different CJ tube preamps consecutively to today's GAT pre):
- noise floor has dropped DRAMATICALLY...shielding, separate power supplies
- dynamics have improved (both macro/micro)...beefed up power supplies and lower noise floor i suspect
- these improvements have provided more detail, more decay, better dynamics, lower noise floor...but also maintained the tube's tendency towards the 'midrang magic', tonal purity that draws so many audiophiles...
In my complete layman's terms, the elements of the tonal purity of tubes were historically enshrouded in a golden glow...and the tech has managed to carve much of that 'fat' away with superior execution...resulting in far greater detail, macro and micro dynamics, decay, lower noise floor...but again maintain the original purity of the tube sound. Thus today, we are benefiting from a combination of tube mid-range magic plus many of the characteristics that 20-years ago were more 'stereotypically' (pun intended) the domain of SS.
In terms of what i hear, my observations on tubed gear (in general but also based on my 12-years of owning 3 different CJ tube preamps consecutively to today's GAT pre):
- noise floor has dropped DRAMATICALLY...shielding, separate power supplies
- dynamics have improved (both macro/micro)...beefed up power supplies and lower noise floor i suspect
- these improvements have provided more detail, more decay, better dynamics, lower noise floor...but also maintained the tube's tendency towards the 'midrang magic', tonal purity that draws so many audiophiles...
In my complete layman's terms, the elements of the tonal purity of tubes were historically enshrouded in a golden glow...and the tech has managed to carve much of that 'fat' away with superior execution...resulting in far greater detail, macro and micro dynamics, decay, lower noise floor...but again maintain the original purity of the tube sound. Thus today, we are benefiting from a combination of tube mid-range magic plus many of the characteristics that 20-years ago were more 'stereotypically' (pun intended) the domain of SS.
garylkoh
WBF Technical Expert (Speakers & Audio Equipment)
Last week, Kara Chafee from deHaviland came and gave the Pacific Northwest Audio Society a talk and demo. She talked about and answered questions about the electronics that were displayed.
The amplifier was a KT88 amp operated in triode mode - with an interstage transformer as well as an output transformer. She said that the design came from 1956, but modern methods and components made it possible to produce at a reasonable price. When the Dynaco 70 was $56 (or $75 fully assembled) the design was so expensive that it could not have been sold.
http://www.dehavillandhifi.com/50a kt88 triode amplifier.htm
The amplifier was a KT88 amp operated in triode mode - with an interstage transformer as well as an output transformer. She said that the design came from 1956, but modern methods and components made it possible to produce at a reasonable price. When the Dynaco 70 was $56 (or $75 fully assembled) the design was so expensive that it could not have been sold.
http://www.dehavillandhifi.com/50a kt88 triode amplifier.htm
I just got off the phone with Bob Carver and I asked him this very question. He was in the middle of something but he did have the time and was kind enough to answer [very briefly] your question, ack. This the quote from Bob .....
I think the biggest change in tube circuits over the years is the extra time, money, and effort put into the power supplies of tube amps and preamps. There is no doubt that tube products have become quieter over the years. In fact, every tube amp I have ever owned was quieter than my Krell KSA-250 amp.
In the heyday of vacuum tubes, we had a gazillion tube engineers that completely understood tubes and tube circuits and they could design tubes to do any damn thing they wanted them to. Take a look through an RCA receiving tube manual and you will glean a little understanding/appreciation for what tube engineers could do. It really is amazing.
Everybody today is standing on the shoulders of the tube giants that came before them. There simply isn’t that much new under the tube sun. We have better passive parts today. The best resistors and film capacitors are better than what our ancestors had to work with. Carbon resistors might sound warm, but they damn sure didn’t hold their values over time after countless cycles of heating. We can argue if output transformers have uniformly improved over the years. The output transformers used on the HK Citation II amps were works of art then and now. Peerless output transformers are still sought after today.
In the heyday of vacuum tubes, we had a gazillion tube engineers that completely understood tubes and tube circuits and they could design tubes to do any damn thing they wanted them to. Take a look through an RCA receiving tube manual and you will glean a little understanding/appreciation for what tube engineers could do. It really is amazing.
Everybody today is standing on the shoulders of the tube giants that came before them. There simply isn’t that much new under the tube sun. We have better passive parts today. The best resistors and film capacitors are better than what our ancestors had to work with. Carbon resistors might sound warm, but they damn sure didn’t hold their values over time after countless cycles of heating. We can argue if output transformers have uniformly improved over the years. The output transformers used on the HK Citation II amps were works of art then and now. Peerless output transformers are still sought after today.
Although there is nothing really revolutionary in the last years tube design, the improvements in the quality of the components and the better computer assisted design tools allowed designers to perfect their circuits and profit from the new better passive components. I have no doubt that the much better recent digital sources, with all the good things that digital can bring also played a significant part in the modern designs.
But as some people say, it is almost all just the implementation.
But as some people say, it is almost all just the implementation.
Thanks everyone for the responses... I am fascinated by fast circuits, the path to which (as I understand it) involves wide bandwidth. So given that tubes can have bandwidth up to an impressive 60-100 MHz, shouldn't they be superior to any solid state design? If not, what are their limiting factors, OTL or not?
Hi Ack...on the one hand, being a tube guy (tube DAC, tube pre, but Class A SS amp)...i am tempted to say "NONE! NO LIMITING FACTORS FOR TUBES!"
but in truth, i think the answer is distortion...i have heard some people say it can be largely second order (which presumably means less disturbing)...that said, i also believe that (just as has been the discussion in this post) some tubed equipment has very low distortion. however, at the limit, i believe tubed-based circuits will have higher distortion specs than their SOTA SS circuits. of course to make great sound, it is probably a lot more than a single circuit's distortion...but that i believe is one of the 'limits' of tubes......please, if anyone who actually knows something technical (full disclosure: not me)...please correct or say something more meaningful.
Whenit comes to pushing the amplifier envelope, I go with Atma-Sphere, Lamm,VTL, and Berning. Direct Treated Triodes to me aare the Holy Grail. So many factors are involvedrice point, technolgy, speaakers.There are some interviews in tas where they claim advnces advances. Transformers and powers supply to name a few.
I am sure I left some company out.
I'm papraphasing but Bob Carver is not high on tubes. He thinks class D holds promise but is not ready yet.
rice point, technolgy, speaakers.There are some interviews in tas where they claim advnces advances. Transformers and powers supply to name a few.I am sure I left some company out.
I'm papraphasing but Bob Carver is not high on tubes. He thinks class D holds promise but is not ready yet.
Hello, Greg. Where did you hear or read this, if you don't mind me asking? All he and Bob F. are doing right now [besides his new line array speakers] is building tube amps. I know the man well enough to know that tubes are his true passion....hence my inquiry.
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Hi Gregadd,
I have never heard any of these...only ARC, Tenor, CJ, Pathos, McIntosh. I nearly got a pair of Berning Ref monos (the big 270watters) to audition, but it did not happen. How do they Bernings compare to the others in your grouping (or mine)? Thanks!
tas did a brief interview wit Bob and a few of the other amplifer "greats." It's in my sisters truck. When she stops by I'll tell you what issue. He describe tubes as colred bu t"fun." That's the danger of paraphasing. Maybe one of the members can scan it in for you.
Thanks! I have always wanted to hear the Quaduature Z monos. i know an Alexandria owner who uses them having auditioned many amps before. He swears by them.
Ack
The limitation in common tubes amplifiers is the transformer.. A transformer is an inductor. The impedance of an inductor increases with the frequency so the tube in themselves could be linear to 100 Mhz but the inductance will simply limit the response of the amplifier in a load..
Now there is the fact that tube are inherently high output impedance device.. To interface them correctly with most loudspeaker you need to adjust the impedance the output impedance of the circuits. Tubes are high voltage high output impedance components.. Most tubes output impedance are in the order of thousands of ohms and their plate voltage in the hundred of voltage... Current is often small most often milliamps. The transformers ... well ... transform this into a lower voltage higher current signal and present a lower impedance source to interface with common speakers... OTL attempts to do the same by placing several tubes in parallel .... they could take advantage of the high bandwidth possible with tubes .. their problems are numerous one of these being DC .. that must be blocked lest you melt the Voice Coil of the speakers .. So most OTL not all are capacitvely coupled to block DC ... There are other ways to block the DC , the Cyclotron (used by Atmasphere) is one and there are others ... Suffice to say that the sheer number of tubes makes OTL somewhat finicky .. Some brands/designs company have attained extremely good reliability with OTL among them Atmasphere and Joule Electa but they are in general finicky ...er. unreliable and tend to go with bang and take away the loudspeakers being driven ..
For the record the best tube amplifer bar none I have heard was the Joule Electa ... The bottom end of this amp is something to behold and the highs rival the best SS amplifiers one is likely to hear.. The modrange isa s sublime as any SET but with in my opinion claity. A surprisingly good amp and one I would consider if ever I was to go back to Tubes. I like particularly the 200 watts model..
Hope I made sense I am watching Basketball as I type this so ....
FrantZ,
I share your admiration for the sound of OTLs. I have lived with two types of Atmasphere OTLs - the original MA50 and a later MA2 mk2. I still miss the sound of them. As you say there was something special in their sound and like a full range electrostatic they had a coherence between all the zones of the spectrum - even the bass seemed appropriate for its type of sound.
The main question when using OTLs is the speaker impedance - they dislike low impedance speakers, and as they do not have low output impedance you should avoid speakers with extreme impedance variations.
BTW, Atmasphere's are very reliable and do not tend to go with bang and take away the loudspeakers being driven ..,. Each triode in the 6AS7 tube is internally fused and in case of tube failure it opens without fireworks. It can be a problem, as tubes fail and you do not notice - you are just getting much less power. At one time one of my MA2's was working on only 16 of its 20 output tubes when I noticed it. The good thing, besides the sound - I could get the 6AS7 at 5 usd each at that time from Russia. The 6C33, however was a more dangerous tube, as sometimes it went in short with plenty of fireworks - a bad habit of some Graaf OTLs . The less good thing of OTLs - the heat!
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