I just checked my Counterpoint Solid-M1 power amplifier and found that it does use MJ15024 in its output stage.
There's nothing wrong with the old technology transistors - its just that many decades have passed since they were developed and new technology (Ring Emitter, LAPT etc. power transistors) leaves them for dead in respect of gain linearity and power bandwidth. This is what gave Japanese manufacturers an undeniable sound quality edge over other manufacturers from the 1980s on.
If you look inside present day high quality linear amps, that's what you find now, too. It's significant that Motorola/Onsemi broke with tradition and developed their own process for these types as we find in their MJL,MJW,NJW series transistors. Their continued success with these products and Toshiba, Sanken with theirs, should tell you something.
Even this new technology is more than 30 years old now but not many changes since then have been as widely successful and popular in high quality, domestic hi-fi amplifiers. Large pro. linear amplifiers are a different matter and with multiple transistors, they can still deliver great sound with those old T03 style, low frequency devices in the MJ150XX series.
If it's to be a linear amplifier, the number, style and grade of power transistors just follows from the specs but the sound quality of smaller amps, say 1-2 pairs of power transistors, can be strongly dependent on the power transistor technology. If all you want is "loud" then it probably doesn't matter what power transistor technology is used, as long as the design is properly engineered for reliability, adequate bandwidth and distortion limits
If you look inside present day high quality linear amps, that's what you find now, too. It's significant that Motorola/Onsemi broke with tradition and developed their own process for these types as we find in their MJL,MJW,NJW series transistors. Their continued success with these products and Toshiba, Sanken with theirs, should tell you something.
Even this new technology is more than 30 years old now but not many changes since then have been as widely successful and popular in high quality, domestic hi-fi amplifiers. Large pro. linear amplifiers are a different matter and with multiple transistors, they can still deliver great sound with those old T03 style, low frequency devices in the MJ150XX series.
If it's to be a linear amplifier, the number, style and grade of power transistors just follows from the specs but the sound quality of smaller amps, say 1-2 pairs of power transistors, can be strongly dependent on the power transistor technology. If all you want is "loud" then it probably doesn't matter what power transistor technology is used, as long as the design is properly engineered for reliability, adequate bandwidth and distortion limits
As the datasheets for the power devices in question states »Perforated Emitter Design«, I suspect that it is no other technology than Ring Emitter by Sanken, just designated alternatively to avoid patend infringements.
The main possible cause that they're no more common in these days might be that there are TO-264 equivalents whose mounting is more convenient.
Best regards!
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