Why no threads on OTL amps?

Let me join Siddh in praise of Atma-Sphere OTL's, neglected in most of this thread. I'm using a pair of M60 II.2's with half their output tubes removed, with Quad ESL 63's, whose impedance drops as low as 4 ohms though is mostly closer to 7. The point being, that's high enough. Not the 16 ohms some OTL's may need. Reliability is fine too. I did an odd experiment, using a Pass Aleph 3 as a monoblock (input and output both paralleled) for one speaker and a M60 II.2 for the other. There was nothing clearly wrong with the Aleph 3 sound, as I switched back and forth on good mono material, but I preferred the warmth of the M60 II.2 sound every time. I wasn't giving up anything, detail, transparency, certainly not palpability if we may speak of that, as far as I could tell. That made me decide I was a tube person for life.

The Berning ZH-270 is just a marvelous amplifier that can drive many speakers with ease. This amp is very musical, quiet, and has lots of drive! The ZH-270 is revolutionary and best described by Thorty40 and Kenl. I love my ZH-270 and would only consider replacing my present system with a Seigfried or Art Audio amp with a high efficiency horn speaker.

C'mon, where are the Graaf and Croft people? And how about the Transcendance folks?

Twl I am also a Transcendent folk, still have it. A great little 25 watt amp it is. This is the one that brought me to the realization of what OTL amps are all about. I doubt that you can do better at the price and power rating.

Regardless of which of the OTL amps that are choosen for a given application and load the one indisputable fact is that these amps as a group are uniquely special. After all, this isn't a p...ing contest, is it? I have not had the priviledge of hearing the Joules, Graff or Tenor but I'm sure they have their virtues and that each might be picked over the other in a given application.

My problem with Siddh's choice is that I can't live in Florida with an increase of 8-10 degrees in my room, the plants would wilt and so would I. I'm sure I could live with its sonics which by all accounts is among the best. But 220 OTL watts, must put out 1200-1500 watts at idle. I guess I could settle for the M-60's, still a lot of heat. This is why I went with the Transcendent originally but ultimately it didn't have quite enough headroom with certain music.

The Atmaspheres, Joules and Tenors may be better on an absolute level than the Berning with a given speaker system. The Berning would be a better choice for me with my speakers and probably would be a better all around choice for a lot more audiophiles. What other tube amp increases power ala ss into low impedance loads? Transformers saturate and compromise the bass and high frequency performance and OTL's start doing crazy things to the dynamics of the music and become unstable into such loads. Well you just add more tubes to up the current. Sounds like a great choice if you live in a cool climate or have a dedicated venting system for the amps. This is the whole point of Bernings' design.

Cool post, Tubegroover. All modern OTLs take the music one step closer to the truth. One comment I would make about the load stability is that the large number of tubes is also an attempt to lower the output impedance of the amp, not just current drive. The output impedance of the Berning amps is 2ohms or less, depending on model. And this is the case with relatively few tubes. This is the real breakthrough in the design in that the RF carrier system replaces the output transformer's task with a much higher turns ratio than possible with iron. Thus allowing fewer tubes, better efficiency, less heat, and a lower output impedance than previous OTL designs. And, it's not really in the signal path, just carrying it. Grid drive. Not cathode follower or circlotron. All new. With previous OTLs, damping factor was a problem because the amps output impedance was high enough to sometimes be above the load impedance and damping was seriously compromised.With a 2ohm output impedance the Berning design breaks new ground with respect to damping and does so with few tubes. In fact, in my MicroZ OTL, the output tubes are 6sn7's. Normally a preamp tube, and a great one. Tube heads out there know that preamp tubes are generally much more linear than power tubes. This is really the first time a linear tube such as the 6sn7 is actually driving a speaker directly. It is amazing. And very short signal path, too. Detail is dramatic. Midrange is liquid, and bass is fast and solid. The sound is balanced from top to bottom. If you just take the sound, not the power level, it is the equal or better of anything there is. I can't believe that I could afford such a thing, but here it sits - all 4 pounds of it! Must be a dream. David Berning is a genius to have thought up this level of tube "groovosity."(As Harvey aka Dr Gizmo, called it)