Ampeg V4.com

I have a ~'73 VT-22 converted to a head, that's been recapped and has all NOS tubes that whenever I power the amp up starts passing a fairly audible mid frequency buzzing noise though my speaker cab. It seems to do this with any cab I try. Two notes, when the amp is in play I have the hum balance turned to about 1 o'clock and if the speaker load switch is pushed a little too far in either direction or not entirely centered on 4 ohms the amp won't pass any signal through the speakers. I doubt that has anything to do with this, but those are the only current problems the amp appears to have.