Dear Experts, I'm working on another cheap 3 tube amp (35W4, 50C5, 12AV6). I'm hearing an annoying hum when the volume is raised. All caps were replaced. It sounds like a ground hum. It's not very loud, just irritating. I replaced all the tubes, disconnected the input source, flipped the ac cord. It's still there. Any ideas? Phil Vourtsis Pres- NJARC