Replace all 4 transistors... Bob is correct in saying this.
You'll have to replace all 4 transistors to bring that amp. up to it's former factory output abilities. You'll require a matched Quad set of SD1446's. Don't just replace the two transistors alone, without changing the other two as well, or the amp may work for a short amount of time then blow the outputs. You require a matched set, commonly called a matched quad set. It's best you let a qualified service man do the job of restoring that amp for you, if you are not a lic. radio technician. Those pills are expensive to replace, so it's worth the extra money to have it done right, by someone who knows what they are doing.
Good luck.
