"Mod", not "mode". The cathode components on V-1 are similar to the 1987/59 but not quite the same. If you change them to those specs it will likely sound more authentic Marshall. In the basic amp circuit - ignoring the special features - that's the main difference I see. As small as this may seem, it's almost the first thing your guitar sees when you plug in and carries through to the speakers, so I'll gamble it's very important.