Sounds like a Sunn Model T to me. Throaty, wide open, fuzz, nice bottom end. Its not going to be a modern high gain monster. The video posted for comparison, yeah I know you said first gen, second gen and most owners will tell you they sound very similar -- different but not that much. And even knowing you did the mod, I'd still think that that beast needs to be really cranked to get the full effect. My buddy has a 76 Orange OR120 and it really sounds great cranked up, same with Matamps, and Sunns (some master vol and some non-master volume amps, but still those older amps even with a master volume just cook better when cranked). My old Marshall DSL that I sold sounded the same on 1 or 10, just louder - was a true new school master volume amp. My Orange master volume is not like that, the sweet spot is on 8 which is brutally loud. I mean here is my Enforcer on about 3 during a break at rehearsal just messing around - doesn't sound nearly as mean and nasty as when its fully cranked (7-8 is my volume for rehearsal
) Point being - my Enforcer has the same volume from about 5 on up, but the fuzziness/saturation really goes through the roof the more you crank the volume.
http://www.youtube.com/watch?v=fa5cT-wvIMI Try to get a higher volume I suppose, kind of hard to tell at that level. Also, seems like a lot of people run modded DS-1s or old school Rats in front of their Model Ts when playing at bedroom volume. I push my amps from time to time with a Black Arts Toneworks Pharaoh Fuzz, its nice to have that take you to 11 and beyond pedal when you really need it or when you are playing at room volume.
If all else fails - go to a different tech and have him look at it. I mean I did that a few years back with an amp and never regretted it. Now I have a tech who knows his stuff and I thought my old guy did!