Not always. The biggest problem you run into is the surrounding circuits are tuned for the spec'd transistor (or vice versa) and a substitute that may seem the same may not work in that circuit. Trust your tech on this one -- he doesn't want to work on this twice.
McIntosh C28 transistor subs
My C28 needs two transistors that are on backorder from McIntosh for months now. Can't a high quality brand transistor with similar (or better) specs do the trick? I do not know the part number of the transistors in question, but my repairman wants to await the arrival of the McIntosh-supplied parts. Your input is welcomed!