I need technical help with my tube pre amp. I would like a schematic for troubleshootingan electronic issue . I am an audio engineering student, and as my project I need to make what seems to be a minor problem. I do need the drawings to complete the repairs or get some idea what might be the problem. The issue is that the warm meters are not being lighted like the other VU meters. I know the schematic are protected and proprietary, and I do respect that, but I have great confidence in this pre amp. Please help .