I built an octal Princeton of sorts last year, which used various bits from the design of a few different early SE octal Fenders. It came out great and I still think it is one of the better sounding amps I've built. A recent thread in the tube amp forum about a vintage 5A3 got me thinking about building a PP octal amp and I dug through my parts bin and found some bits and pieces that might work and whipped up this schematic: I've used the basic bones of the 5A/B/C3 deluxes, but with a few alterations to make it more interesting. I'm using a 6SL7 instead of a 6SC7 for the input tube so that I can split the cathodes and have both a grid leak and a cathode biased input channel. I've also put a switch on the NFB so that I can have that both ways as well. Lastly I'm using a power transformer, field coil speaker and PP 6k6 transformer pulled from an old radio console. I figure that all together this should give me something like 8 watts of output and be a bit quieter than a 2x6v6 amp while covering the full range of octal deluxe tone options.