1977 100W Marshall JMP Mk2 2203 - "Arlene" Amp

I take a first look at a "1978" Marshall 2203 JMP Mk2 purchased recently on eBay. Found that it's actually a 1977, not a '78 as the seller advertised. The PCB is signed by "Arlene" whose signature I seen on other amps I have. Like the other Arlene amps, the wiring is neatly done. The amp appears to be unmodified except for possibly the output tubes. I power up the amp for the first time with 2 of the 4 output tubes installed, and test with a guitar.