Original 1973 Otala Schematics

Note the hand-drawing on the schematic. First attempts at traditional current limiting can be seen — this was soon discarded. Note also the extra resistors near the output: the loudspeaker was to be coupled between the output terminal and the small 0.1 ohm resistor to ground. This was a later idea (I don’t remember when it was introduced) which would give some current feedback in addition to the traditional voltage feedback. The effect would be to make the loudspeaker “invisible” to the amplifier.

Note that you can see the prices on the transistors here: NOK 4.70 in qty 100 for BD203/204. Cheap transistors!