Are tube designs still evolving, or have all circuits effectively been invented?

[egidius]

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???

I firmly believe that David Berning would need to be quoted here as one of the foremost tubedesigners.
Albeit, I do not understand his design, the few that do, call it groundbraking.

I own A ZH 270, ZH230 and his ZOTL Pre..

[FrantzM]

Micro

Quoting me

Some brands/designs company have attained extremely good reliability with OTL among them Atmasphere and Joule Electa

... They prefer higher impedance speakers. I remember there was a fellow in NY who had the Soundlab driven by Atmasphere and I really liked the sound.. Then, its Soundlab had a nominal impedance of 16 ohms Beautiful sound.
As for the heat ..I had forgotten about that part of the OTL equation... he had a special vent over his amplifers and that might have cost the price of the amps to install it in his condo

For what tubes seem to do I sincerely believe Hybrid designs are a very good compromise... you take away the pesky and frankly limitative transformer and replace it with good old SS... Question do the Lamm and Tenor use FETs in the output?.. Those have been my favorite Hybrids, although I did find the bass of the Tenor too "light" for my tastes preferring the more robust presentation of the Lamm. I must also say I was taken by the sound of the Moscode amplifiers.. They were very popular at one point but seem to be less so today.. I did like the way they sounded and the sane price... We , audiophiles go throuh some lemming-like modes .. We just follow the brand/s of the day and just drop it/them without much questioning or auditioning...

[FrantzM]

I firmly believe that David Berning would need to be quoted here as one of the foremost tubedesigners.
Albeit, I do not understand his design, the few that do, call it groundbraking.

I own A ZH 270, ZH230 and his ZOTL Pre..

he's been innovative for several decades. Too bad his current offerings look really bad and amateurish... I quickly add that I haven't heard these but they look cheap...That says nothing about their sound but if looks could kill ... well it is severely limiting Berning's present products acceptance IME ..

[Steve Williams]

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 ....

I'm watching the same game as you Frantz

Go Lakers

Here's the Lamm info

http://www.lammindustries.com/PRODUCTS/m12spec.html

Here's a look at the transformers on my amplifier and it's separate power supply (dual mono/dual power supply) at 32 wpc. I understand what you mean

http://www.lammindustries.com/PICS/M...20modified.jpg

[jkeny]

For a completely innovative new tube circuit, have a look at John Swenson's Beam Deflection Tube preamplifier - a phase splitter & volume control in one tube. There are many interesting aspects to this preamplifier: it uses solid state devices for constant current source biasing; the volume is controlled by the voltage on a grid plate so no potentiometer in the signal path. http://db.audioasylum.com/cgi/m.mpl?...ght=bdt+preamp

[Gregadd]

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.

tas May/June issue p.54

[treitz3]

Thank you. I will see if I can obtain a copy.

[Mark (Basspig) Weiss]

I don't know how many TOTALLY transformerless VT amplifiers are on the market, but I am working on a design based on Russian horizontal sweep tubes for a direct drive. The amplifier will be DC-coupled througout, utilize a solid state Schottky-based rectifier and DC filament supply. As such, it should be the lightest weight amplifier of this type, and economical to manufacture.

[puroagave]

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!

knock on wood my Graaf is going strong with 10-yrs use (im not the orginal owner) and no blown caps or repairs. the Joule Electra OTL also uses the same 6c33c tube and the sound is stunning as Franz suggests. I had an early pair MA-1 Atma-spheres driving Celestion SL700s - by far the best sound i ever heard from them. a paring, which on paper shoudnt have worked.

[JoeyGS]

John Broskie's Aikido could fit in as one today's new tube design. I am a fan of his Aikido preamplifier which I think is clean sounding (not clinical), dynamic and can handle most sources and amps. Below is an excerpt of the description of Aikido's topology, taken form the following link - http://www.tubecad.com/2011/12/blog0220.htm

Here is how I described the Aikido amplifier topology at its introduction:

"The broad-stroke explanation of the Aikido amplifier was that the circuit eliminated power-supply noise from the output, by injecting the same amount of power-supply noise into the top and bottom of the two-tube cathode follower circuit; that the input stage (the first two triodes in series with each other) defines an AC and DC voltage divider of 50%, so that 50% of the power-supply noise is presented to the top cathode follower’s grid, while two equal-valued resistors in series also define a voltage divider of 50%, which feeds the bottom triode's grid the same 50% of the power supply noise. Since both of these signals are equal in amplitude and phase, they cancel each other out, as each triodes sees an identical increase in plate current, so the output remains steady in spite of the power supply voltage fluctuations."

I think John B. did a fantastic job in this preamplifier and am very happy with its performance. Now he has the Aikido Cathode Follower (ACF) which can be utilized to bridge sources and power amps into preamps improving the impedance matching between the components. Actually, the Aikido preamplifier has the ACF built into it and which makes component matching easier.

John also has a lot of design that might interest your fancy.