I just found an mp3 of a recording I made of my Marshall amp with the two Chinese 12AX7 B preamp valves installed in it, so here's a link to it, this is what the Marshall amp sounded like before I swapped-out the preamp valves for the Gold Lion 12AX7 valves:
I'll see if I can do a demo recording of the Marshall amp with the new valves installed in it tomorrow, will post a link here once it's sorted, so stay tuned.
And just for interest, here's a demo recording I made of my Marshall amp before it got fixed after blowing fuses at random times, the preamp valves I had in it were the original Marshall brand ECC83 valves that were installed in it when I first bought it, here's what it sounded like: