for the same maker like Yamaha, different of their models will have different designs and technology so it is hard to really go by brand alone, the model number will tell you more...
the life cycle of semiconductors in japan are very short indeed, the moment these semicon houses recoup of the RnD and foundry costs, then end of life for such device soon follows, planned obsolescence if you will...
unless of course there is a huge demand, in which case Toshiba for example gives out licenses to ON semi of Fairchild to manufacture such devices as the 2sv5200/2sa19743 power trannies, which have gone down in price due to high demand and huge inventories...
also for the same era, different makers will have the same topology from brand to brand,
why is that? you may ask, and that is because the semicon manufacturers of the time period comes up with new devices and with is reference designs.....this is the same as with video card chip makers, nvidia or another will come up with a reference design and vendors work on that with their own idas...the same goes for audio, the devices that are churned out by the big semicon