My new 68 Custom twin is not working, I took it home sat when I switched it on didn't really hear it working, just a slight hum just like when you plug a guitar in the amp and the guitar is isn't plugged in. I checked the tubes I believe its a 12at7 in the V3? and there's a at7 at V6 which is the PI I think? Rest are 12ax7. The tank is plugged in the right way also. If I cant figure it im going to take in Thursday the store owner said they should be able to check it out that day. Any ideas?