Congrats! I have a JCM-900 4100 "5881" that is a fantastic amp. I know the Marshall purists are always down on the 900's and especially if they have the 5881 tubes, but they're fantastic, versatile amps. Some folks suggest that jumpering the effects loop provides tonal benefits on this amp, I'm not sure I ever noticed a huge difference. Might be something worth screwing around with.