The 2SD555's are about as robust an output as you can find. They are half the complimentary pair in a lot pof amps from that era including the Spec 2. Ed has researched that a bit and toweards the end even PL started going with the 2SD555/2SB600 complimentary pairs. Back then they were known as a hot rod, what they didn't know was that they would be hot rodding 40 years down the road.