OTL amplifiers

Dfrigovt, since much of what has been posted here is way outside the scope of what you originally requested (especially from me) and is probably very confusing, let me answer your question more directly as pertains to Atma-Sphere M-60 Mk. II.2 amps.

Advantages: high-resolution, effortless sound; extended in both directions, rich (but not syrupy) and dimensional

Disadvantages: speaker choices are more limited, unless you use a large OTL or a corrective device like the ZERO autoformer, and possibly heat (hasn't been a problem for me though)

Since there are plenty of excellent speakers out there that work well with OTL's, I don't see OTL's as being problematic in any appreciable way.

BTW, do you have a particular speaker that you would like to pair with an OTL?

Henry to answer your question, this might be a possibility if there is not a built in circuit or shut off in the event of catastrophic overload, a voltage surge from the outputs. Most OTL amps have some sort of protection circuit in the event this manisfests itself for any reason.

I see you have asked this question on another thread and no one has answered. Maybe you should talk to a dealer. I believe Jtinn is a dealer for Tenor and he should be able to answer your question. This was one of the problems with the Futterman's, it didn't have protection between amp and speaker not to mention its inherent instability when matched to the wrong load. Most of today's OTL's have addressed this problem and do have some type of protection.

Said simply in general

--OTL-s give out full power only at specific optimal load. If load drops they loose the power so the bass is weak weak weak. If impedance goes up the output peak power increases to the point that it might damage speaker. Problems with DC at the output are also added in some OTL designes.

--OTL-s are tube abusers where tubes work under its peak values and deadly deadly hot(low plate voltage and high POSITIVE gride voltage) so there is the reason of OTLs to be so hot and expect to change tubes(input tubes and power tubes together) more often than you change oil in your car. Wanna try NOS and see how it "shines"? Tubes might age differently and if OTL loosing balance it can also damage speaker so there we have a large reliability issues.

--There is a solution for OTL amps that relatively recently was in effect to implement the current transformation using solid state inverterting amps that allow tubes to work as a main amplification devices and so efficiently transofrm voltage to current to drive today's speakers. The input stages are also implemented with differential cascade using transistors since input tubes also require reverse
connection for OTL-s. Such OTL consists of differential input SS circuit, Amplification circuit(tubes PP or SE or SEPP in normal common-cathode connection) and output SS inverter. The only problem with SS inverters and drivers that someone would say that he/she's listening to SS instead of tubes. Well, these meanings are only stereotypes and in reality we're listening to the product that was designed for a specific characteristics objectively and music subjectively. The design I studied from the following page:

Hybrid OTL 150W/ch amp

Please note that japanese readers will benefit much more from that page than non-japanese since description of design is only written in japanese(figured from .jp domain he..he..).

I don't know how truthfull are the characteristics of such design as well as I don't know how this amp sounds when implemented, but my objective review just only based on schematics and characteristics makes me to conclude that this product realy should be reliable and great sounding after implementation. Moreover it runs "colder" than many of SS amplifiers and has a larger design room for larger power but certainly with sacrifice of reliability.

--Zero tube autoformer does nearly the same as SS inverter but with much greater loss, larger neg. feedback and distortions. Sorry but tubes arn't flexible enough to be as a dynamic load.

--Last thing pure tube OTLs are great with headphones.

Some thoughts about reliability and feeding tubes to an OTL faster than spark plugs to a Hemi...

I would be out of line to speak about amplifiers other than the AtmaSphere M60, but I can tell you I have nothing but the utmost respect for what Ralph Karsten has designed.

I have to say that when he says his amps are all but bulletproof, BELIEVE HIM! The literature states that pretty much no matter what goes on, it will not take the amp or your speakers out. That's a fact. It may cost you a couple of fuses while you are learning about biasing, "zero offset", or not shorting the amp, but that's about the worst of it.

As to tube longevity, the prototype of the AtmaSphere M60 is supposedly still running its original set of tubes - 20 years later! I kind of stupidly used one suspect tube(thanks Sovtek...). It was fine for a while, just had a permanent bolt of lightning out to the glass, and pulsated strongly with the music. But, when I ran another pair of amps for 2 months, and put them back into service, that tube just didn't feel like being social. It did all kinds of misbehaving, time after time. And despite some really awful pops and bangs, true to Ralph's word, the tube's pyrotechnics didn't harm my amp or loudspeakr in the slightest - try that with a Futterman. Other than seeing this kind of once in a while Soviet QA, the 6AS7G tubes last a long, long time.

Thanks everyone for your input. The discussion went well beyond what I was looking for, but that's not a bad thing. My feeling right now is that these things are far too fussy for my liking. I am willing to work for my audio heaven, but I do not want it to rule my life. Changing tubes frequently, searching the ends of the earth for the proper speaker, blowing speakers, etc. is not my idea of nirvana. Thanks again, all, for the insights.
Dave