Lookin forward to hearing how your thoughts and experience with the tube swaps. Also any other changes or mods to the 400+. One random thought I've kicked around: since I never use the effects loop on my 400+, I'm wondering if (i) it's feasible to either bypass the parallel loop completely, or change it to serial, and (ii) if there'd be any benefit to doing this. My crude thinking is that (generally) less circuitry in the path is better, and since I never use the effects loop (which AFAIK since it's parallel, means it's always at least partly in the signal path, even when dialed-down... that right?), so it's expendable... or something like that. Then again... it's an amp that sounds good as-is... why mess wit it?