I just got this amp from a Thomas organ and while checking voltages I found that I have no voltage on the bias line. The schematic shows I should have -15v but my meter reads 0. I have only turned it on for a short time but it did seem to work ok while it was on. I did have the 25vac but I get +35vdc on the + side of C702 but 0 on the other end when it should be -15. What would cause this?