I have the MusicMan HD150 head and was curious how old it might be. It has the 6CA7 (4) tubes. I've looked at other pictures online and the Musicman logo plate appears to always be located top left on grill with the model plate in the lower right side. Mine are reversed locationwise. Not sure what that means but thats the way it was when I got it about 2 years ago. Serial number on this is A005104. The logos are black backgound with silver letters.