I've found an Italian company who offer an OTL valve amplifier.
The product page is this (translated in English by Google) :
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I would read opinion from more expert users about this amplifier that is based on a single tube 300B for channel and that outputs 250W.
Consider the final phrase that states :
"ALIENO 250 LTD is not a hybrid tube & transistor amplifier!
The innovative LTD "Loudspeaker Tube Direct" technology allows the tubes to be used exclusively for the amplification circuits, while the transistors are used exclusively for power supply and protection circuits."
This sound very strange because the 300B tube anode current is in the range of hundreds of milliamperes, not capable to generate : "Output current: > 100 peak Amps per channel."
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The product page is this (translated in English by Google) :
Google Translate
I would read opinion from more expert users about this amplifier that is based on a single tube 300B for channel and that outputs 250W.
Consider the final phrase that states :
"ALIENO 250 LTD is not a hybrid tube & transistor amplifier!
The innovative LTD "Loudspeaker Tube Direct" technology allows the tubes to be used exclusively for the amplification circuits, while the transistors are used exclusively for power supply and protection circuits."
This sound very strange because the 300B tube anode current is in the range of hundreds of milliamperes, not capable to generate : "Output current: > 100 peak Amps per channel."
😕
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About the hybrid hypotesis I've found another page where the amplifier is reviewed, at the end of the page there is a little schematic about internal circuit.
si audio041114
From that image it seems that the out signal of 300B is current amplified.
But considering that the out signal of 300B is the audio signal and that the output current is not DC but is true audio could not be true that transistors are not used in amplification circuits.
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Could it be, only an ac power line watt eater. But I think that people who pay 45.000€ for that product would accept a such heater.
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Just thinking about the conversation I'd have to have with the missus if I bought those speakers makes my blood run cold.
There is a bit of 'Spinal Tap' going on there, I think.
Stretching the truth a bit but it could be a tube driving a class D or H amplifier. Think of a modulated switching power supply.
About working class the page says "Class A OTL" that weights "220.4 lb".
Not exactly a class D amplifier about weights.
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Are a current source which measures the current through an output resistor. That current source is probably the real amp. The 300B is there for a bit of distortion and a good glow.
I think you are right, also if the original idea was to "replicate" the sound of a tube amplifier with a transistor amplifier all the amplification chain is useless. They could have used the output signal from the first tube the ECC82.
I find all the "product" a little unfair.
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Do you think that avoiding the cathode follower circuit and using the signal on the anode with a resistor would be possible to reproduce a valve amplifier sound using transistors? In other words, it's possible for you to "amplify" a warm tube "sound" using transistors?
A simpler solution is to make a preamp with a bit of 2nd harmonic distortion and put it into a class 'D' amp. I think you feel your getting something with a 300B. Find some old style valves with some good glow and hide the 'D' amp underneath.