Reading from a few people that the Excelsior appears to based on a cathode-biased 6G2 brown Princeton I compared the schematic/s and indeed they're very similar, down to measured preamp voltages. The Excelsior has a sort of ratty tone the one and only Brown Princeton I've ever heard didn't. The biggest difference is the bias resistor on the two halves of the first preamp tube - 100k for the 6G2, 220K for the Excelsior. That's trying to drag a lot of gain. Mine squealed if I face it with my Tele above about half or click in too much gain. It also tends to saturate heavily as soon as you have decent volume. There was headroom but tricky to manage. I've temporarily jumpered 220k parallel resistors across R5 and R7 in this schematic - so they are 110kohm measured. Far from losing gain or volume, it appears to have picked up some volume, or else the ratty sort of fuzzy distortion was due to too much gain saturating the 12AX7 halves. It's now fuller, smoother, feels not so hard/laggy to pull tones out of - more touch sensitive, more pick responsive. That hard garage-grungey tone is still there but more controllable - if anything, it's throatier and fuller but more transparent. The Tele sound is more prevalent. But Keef is a little more dig away! Now I know this works I'm going to pull the PCB and solder 100kohm resistors in properly, and I think I'll change the 1st bypass cap to a .022 as well as per the 6G2, as I think that might smooth it out a bit more. I don't know if it's louder or just its got better frequency response. I've wound volume back from 7+ to about 6. The bass is certainly more apparent. It reminds me of nothing so much as - a Marshall, crossed with a bigger, throatier 5E3!