if i recall correctly, the power outputs are matched pair pnp/ npn transistors in a push- pull configuration.
as usual, rat shack carries the cheap korean throw aways - steer clear of them. they sound horrible. usually, good amps have an auto biasing circuit to adjust idle (quiescent) current in the push- pull pair. class AB amps can develop absolutely huge notch distortion (at the point where the pnp transistor and the npn transistor are both in a conducting state slightly above and below the center of the + and - power supply rails.) i used to be so anal as to buy 20 sets of transistors and test them individually in an engineering test rig to obtain the closest match. i'd also match the caps and resistors in the biasing circuits and the diodes used in the auto bias line.
the techy members are probably gonna' kick my butt about my methods, but remember, i don't repair electronics for a living anymore. when i rebuild engines, i'm just as persnickity about balancing weights of moving parts and polishing surfaces.
2n3055s were very popular in high current servo controls and as power pass elements in the 70's and are still used in replacement automotive devices, hence their availability. the 3054 or 3056 devices are up to 20 times the cost of the npn mates.
there are a number of etail electronics suppliers, mouser was just a personal favorite.
best regards, tube
