Vintage DD turntables. Are we living dangerously?

Doron,
I have always been curious about Joule OTLs, maybe because it's the only brand of OTL I've never owned or heard. I started with Futterman amplifiers in the 70s, owned many variants of the Futterman circuit, and now for the past 10-15 years have been using Atma-sphere amplifiers, as you can see. Most of my audio life has been OTL amplifiers driving ESLs. Lately, I've been enthralled by a pair of Beveridge 2SW speakers, driven of course by the built-in Beveridge amplifiers, which are not only OTL but also direct-drive. Amazingly good. The Bevs constitute a "second" system, in my basement. Atma-sphere/Sound Lab system is in my living room.

Well, I may now be the only one here who still does not have a completely reliable TT101. I can make mine work, but I would not say it is reliable, at all. I do have an idea of the problem and how to fix it, but I have too many projects, now including to complete the restoration of a 1959 Alfa Romeo Spider that's 95% done. To add insult to injury vis the TT101, its UA7045 tonearm seems to have a shorted wire somewhere inside. To use the TT101, I will now need to replace the tonearm on the QL10 plinth. Fortunately, the pivot to spindle distance for the UA7045 is close enough to that of the FR64S that I can sub the latter into the QL10. But since I love music more than tinkering, I tend to crank up the old reliable Lenco with Dynavector tonearm/Acutex LPM320 cartridge (muchas gracias, Raul), driving the Beveridge system via a Silvaweld phono stage and Klyne 6LX used as a linestage. The QL10 just sits there.

OTL driving panels is surely a very good match. I have heard McAlister Audio OTL 195 driving Acoustat 3 with great ease (not an easy feat with speakers that swing impedance from 0.5 to 40 ohm!). King sound, like wise.
The Beveridge are very insteresting design.
I am not a panel guy but do appreciate their incredible transparency, their mid-top end coherence and their big sound stage.
I still like my "box colorations" and my trusty mid-bass:-) a matter of personal taste.
The Joule OTL is fairly full bodied OTL due to some 5751 driver tubes. With the Joule LA-100 Mk III premap its a very sexy/sensual sound (not muffled but very liquid) and a match made in audio heaven for my taste. Not sure the Joule is panel material though. Maybe the more powerful monoblocks can handle the low impedance but these take a lot of real estate and you could sell your furnace...
Someone wrote a beautiful piece about the Joule OTL's. I agree wholeheartedly:
"audio shows take the romantic sheen of cute packaging and sales literature very quickly. Once fatigue and impatience set in, you discover how much mediocrity is being promoted, and how few designs rise above the fray. The Joule amps exceeded my expectations. The second I heard them, I immediately knew what was missing from nearly every other amplifier on the market. This was the only amplifier I heard that could keep all the harmonic information together in one coherent image. It sounded like other designs were suffocating the harmonics, but hiding the damage behind oversharp highs or thumpy bass. The Joule is technically underdamped, but the bass has the rare quality of being tuneful, rather than punchy or visceral. This ability to be true to tone is the great distinguishing qualty of Joule. The complexity of piano strings is fully revealed instead of glary banging. Large stringed instruments have "cavity" , as if you can hear whats happening internally in the instrument. If classical music or acoustic music of any stripe is you favoured listening, Joule will absolutely ruin you for any other amp. It is the most civilized tube design in the world, if not the coolest running or easiest to live with. This isn't a toy, and it isn't ultra-convenient. You won't want this for ear-crushing boozy gatherings or adolescent angst sessions. It is an adult experience in the best sense of the word"

The impedance of any ESL is a complex function of many factors, but basically an ESL can be viewed as a giant capacitor. Thus it will tend to have high impedance at low frequencies, and the impedance will tend to fall off at the very highest audio frequencies. More than one ESL measures 2 ohms impedance or less at 20kHz, for example. However, that same panel may well measure 100 ohms at 20 Hz. The step-up ratio of the audio transformer is also a major factor in impedance; many if not most "modern" ESLs present a relatively low impedance load as a deliberate design choice, to make the speaker more friendly to solid state amplification. Martin-Logan speakers are a particular example of this. The impedance seen by the amplifier will vary inversely as the square of the step up ratio of the audio transformer. So choosing a high-ish step-up ratio will tend to result in low impedance even across the mid-band. Crossover networks also tend to reduce impedance around the crossover point. My point is that your Joule amps can certainly drive any ESL that is built or modified to work well with a tube amp, i.e., any ESL with a decent impedance curve (e.g., >8 ohms) at low and mid-frequencies. There is little electrical energy required at 20kHZ, so a very low impedance at such high frequencies is nothing to worry about. For example, my SL speakers measured impedance at ~500Hz in stock form was about 5 ohms or less, not good for an OTL. When I removed all the crossover parts from my SLs and substituted the treble audio transformer with a full-range audio transformer, the impedance now measures 20-25 ohms at mid-frequencies. Needless to say, my Atma amps are in OTL heaven driving my 845PX speakers. And the improvement in sound afforded by getting rid of the crossover brought tears of joy to my eyes.

Try an original Quad 57 or a KLH9. Those great speakers were made to mate with tube amps from the get-go. You will be amazed.

Hello Lewm,

I am well aware of the potential. Acoustat had model X which had the OTL directly driving full range panels.
My "issues" with panels are not how hard they are to drive.
I am well aware of their strengths. My issues is maybe my own personal perception but panels always make me analyze the music instead of listening to it and immersing myself in it. They give me an illusion that the voices come from outer space but the cavity of instruments are missing somehow as if the cavity was blocked or instruments were much flatter than what they really are. To me they sound like they miss the resonances of a stringed instrument but panel guys will say I miss box colorations, which is maybe the case.
Hard to explain why panels sound like that to me, but perhaps it has to do with mid-bass cancelation due to the dipole construction (destructive interference in physics). In addition, I always panels as coherent from the midrange and up but not so from lower mid-range to the deep bass.
I believe that some people are more sensitive to upper frequencies and some are more sensitive to lower frequencies and then you have the horns, which I could never warm up to due to my own preferences in sound reproduction.
In the end, at the highest echelons of audio, when clarity is achieved, our hearing and perception defers and everyone has his own preferences.
Otherwise we were all owning the same exact system, which would have made this hobby pretty boring…:-)

Doron, I misunderstood. Some people like olives and some don't. That's cool. As for me, I have yet to hear any box speaker I could live with, knowing that I could also have what I do have as an alternative. (I don't use the term "panel" speaker, as there are many kinds of panel speakers, e.g., Magnepans, which I do not wish to include in my endorsement. Nor do I feel the same enthusiasm about all ESLs, only certain ones.)