Jeff K- when you say gold box, are you talking about the empty IR laser housing with the thin silver lid?
Thanks for looking into the tube type, I know Wizard and I have been discussing the circuit topology and what I recalled it being. You just confirmed my memory of what it was. That tube is the equivalent of the venerable NOS American/European made 6DJ8, one of the most popular current drive medium/low gain tubes ever made.
So that pretty much settles my suspicions Wizard, I am almost certain it is a cathode follower, 0dB or <1 gain, line drive preamps. I doubt you'll want to attempt trying to modify it to accept a 7075. Besides the pin out being so dissimilar all of the Load, bias, and grid leak resistors would require significant value changes just to make it work even poorly. I suppose if your planning to drive any one of the thousands of solid state amplifiers out there with an input impedance of 50k or more it could be made to sound ok. Trying to drive a <20k load would be less than desirable.
I'm pretty sure they make a converting socket for the pin out of this tube and the 12A## series somewhere. I've also seen people take an old dead miniature 9 pin tube and crack off the bottom shelf with the pins and solder them to the bottom of a 9 pin (even octal 8) socket and make their own converters. This would probably be the easiest way to try your experiment with the 12AX7/7075 class of tube. Then you could also try the 12AU7 which would work probably as a direct replacement aside from the pins, and sound really good with some value adjustments on the load and bias resistors.
Also, now that I know the tube I can say with a fair amount of confidence it was probably set up to run an HT of 120-150v.
All this tube talk has got me revved up again over glass electronics. I may try to design a laser diode driver using a tube circuit to regulate current. Since there's no tube I am aware of that will come close to being able to operate in the range of <10v and at currents as high as used in the more powerful diodes I like to play with, it would require some sort of hybrid tube / pass transistor arrangement. You think you could SPICE me up a circuit like this? I mean you are the only Wizard I know with an electrical engineering degree. You should just be able to wave a wand over your keyboard and make one materialize on the screen. I'm thinking why not an M140 running at a solid 1.8a. Give it some thought. This would make an awesome addition to my Steampunk Lumia. Imagine the beautiful orange and blue glowing tubes perched somewhere clearly visible and paired with a couple blazing collimated beams of photons tuned to the red and blue spectrum. I'm drooling over my iPad as we speak....