Gibson BR-6 amp

[dkevin]

I was in a local (Seattle) guitar shop and was pleased to find several older Gibson guitar amps for sale. One in particular caught my eye. It was a BR-6 amp from 1952-53. I have one of these and it is a very sound amp. This one however had a curious addition. The BR-6 and 6F have 5 octal tubes laid out in a straight line. The chassis is located at the bottom, rear of the cabinet. This amp has 5 octals all right , but also has a 9 pin (noval?) socket tucked in behind the preamp octal. It appeared to be a 12AX7 tube. My first instinct was to suspect an owner modification to increase the preamp gain. But the socket appeared to be of the same vintage as the others. I looked for another schematic but the only one I could find was the 5 tube variety. It may well be a home-made mod but imagine the surprise of the new owner when his tech tells him that his amp is not stock. The asking price is not low. I did not mention the issue to the shop salesperson. Let me know if you have encountered older Gibson amps like this one.....Gibson_br_6.pdf