Good afternoon folks. I have a 60s National Valco solid state bass head that has 3 diodes that cannot be identified by the best repair guy in the area. I have absolutely no idea what the diodes are, the repair guy said they run with the output, and on the diodes are a 5, a T, and what looks like maybe an L or a 7. I was just wondering if anyone can help me out before I toss the thing for good. I've attached a couple of pictures of the diodes, and the bass amp circuit board, with arrows pointing to the locations of where the diodes should be.