Is'nt this just a current loaded buffer, maybee also a current loaded VAS stage before this ? The mpsa 13 the current limiting transistor for the active load. Probably its class A. 1,1-1,2v ube. near 12 mA in tr23 There is many ways to achive class A and this is just one of many for many different stages. As such it dont seem to have any (significant) advantage over other commonly used low open loop gain/low lockal feedback in the output stage.
BUT : if the current limiting transistor also has temperature feedback as it will. And the overall dc performance is achieved thru overall feedback, but is most definetly coupled thru temprature. But then it will alter the biaspoint also for the innput stage as temperature alters. If class A is the goal there will still bee 'small' changes. ie sin tone to full output at klass A settup load the temp in the output stage would make a small drop (for most commonly designed class A stages). And again altering the reference bias point for the input stage, as balance is concerned dependent the rest of circuit. For the buffered stage altering the constant load and for the output stage the bias is altered. Hopefully this is most elegantly designed and stable, this is werry hard to achieve and i sertainly dont tink it is possible under all the varius loads and enviroment.