I just bought this old B15 from an gentleman who played it back in the day... He says he bought it in the '60s, and that it is all original. So far I've checked the EIA on the speaker and it seems to check out (137(CTS)651). However, the cabinet seems odd. I can't find any images or information that explain the form and placement of the logo, or the piping on the front of the cabinet. Ideas?