I have removed the amp portion of the combo from the frame to check the health of the 12ax7 tube.  I pulled the tube from the socket, looked fine so I put it back in.  I also removed the reverb unit and left it out.  Now when I plug my guitar in I only get a very faint and quiet signal even with all knobs cranked to Max.  Strangely, the signal actually gets slightly louder with the master turned to zero!  Came someone please help?  Thank you.