My 1960 Seeburg had a similar problem that turned out to be a blown tube. The amplifier does have at least one fuse. These are mounted on the front or top. Twist open the black plastic cap (pushing in as you twixt ccw), remove the fuse and test with an ohm meter. To test vacuum tubes, a good way to start is to look for a cool one if the others light up.
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My 1960 Seeburg had a similar problem that turned out to be a blown tube. The amplifier does have at least one fuse. These are mounted on the front or top. Twist open the black plastic cap (pushing in as you twixt ccw), remove the fuse and test with an ohm meter. To test vacuum tubes, a good way to start is to look for a cool one if the others light up.