OTL amplifiers

...so basing on pricing of OTL amps you can easily get an output transformer with ferromagnetic core taken from the Moon(99.9% carbon-free iron only currently found on Moon) and brought to the Earth to make tube amp much more efficient and cooler running.

bottom line is large buck for the small watt.

OTL bests with ear-speakers. There I see no compromise whatsoever.

I'm OK with SET
I'm not OK with pricing of SETs that basically require a knowlege of elementary school graduate to build them. Should be at least 10x- cheaper. I'm not OK with pricing 300B triodes as well.
As to OTL's distortion-free listening I'm OK as well BTW SET and OTL are completely different since OTL-s use mostly push-pull circuits except probably for headphone amps.
It's not OK with me the rest of inconviniences and again pricing. I agree that Bearnings are priced OK and could be the exception from the rest of OTLs.

Now I do realy have a question about DC at the outpu on OTL-s... Is there an output capacitor I assume?

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.

I was realy speaking in general terms of OTL designes. In particular the protection and auto-bias circuits are implemented either using tubes or transistors depending on model. Amps that are pure tube-OTL with all implemented protection basically overwent tough reliability issues but "naked" tubes still drop the power twice when impedance drops twice and that's in the nature of all "naked" tubes.
OTLs can realy be used successfully in bi-amp applied for active systems where there is no need for higher power i.e. for freequencies from .8k to 20k and that's where most of our ears hear the best clarity resolution.