Elizabeth is asking the right question. Have you lost sound in one channel regardless of which source you are using? Do you still get full sound in both channels using your TT?
In addition to rechecking your connections, you might try re-seating--or even swapping--tubes as well. You might have a dead tube.
This unit has just one fuse, right? I have a VAC 70/70, which has fuses for each side. When I lose sound in one channel, a blown fuse is usually the culprit, but I don't think that applies in your case.
Good luck with your troubleshooting!