> applied -18VDC to the Left output
The transistors, you don't *need*. They mute a start-up thump. Just cut the collector leg, they have no effect (and you should have your Volume down at power-up). You can, first-approximation, replace with "any" Si NPN and get mute back. (The specific part may mute 50dB instead of 40dB, say.)
But hum suggests you did further damage.