hmmm, you may have a point with your run wet idea. The axial flux would be an ideal candidate to run under water. Just make the mag rotors fully epoxied to protect the mags and give it a flawless disk profile (no resistance to the water). Make the stator with the wire outs very very long with no turmination screws. Straight out of the epoxy and up the bank to the rectifiers. There should be no problems with this at all if you construct with soggy end in mind. Stainless steel bearings are available for the shaft or because torque is in abundance, proper bearing buddies and modified hub seals may get enough sealing to keep the grease in.
That still leaves you with rpm problem. Paddle wheel will provide torque at very low rpm. At 14', each turn will cover approx 44' of diameter. Each water mph will pass 5280/3600 feet past the mill each second. At 1 mph thats around 1.5 feet per second. I'll leave it to your imagination how many seconds pass before the 40 or so feet of the wheels perifery get pushed around at this rate...but it can't be pretty.
Perhaps looking at the screw option will give you something better in rpm terms, although in 18 inches of stream, your diam is very limited, and may not give you enough surface area at this water rate to do much power at a high "tsr"...dont know if thats the terminology for water screws.....looks like gearbox is hovering on the horizon.
6BQ5.... now thats going up market, i didn't see too many of those in this country (australia) They were considered very flash a good 6 watts in A class. I used them for some of my projects, but a lot of sterograms in this country even 6BL8's on the outputs in A class...about 2 watts i think, the classier ones were 6GV8 in the dual packet gear, but a lot were 6AQ5, cheap and nasty but tidy offspring of the 6V6. Over here 6BQ5 were at the top end of the A class power outs, after that it was AB1 or Bclass. Didn't see too many of these here, as the transistors arrived late sixties and moved the expensive heavy power outputs out of business, but the economic 6AQ5 lived on for a longer while before being shaken out of operation in the early seventies.
Disco, yes the only time I saw these was to fix amps, and to design lighting systems with the "musicolor" effects. A thousand watts a channel made my eyes pop the first time after being used to 3-4 watts. And then they had three of these per channel Bass,mid, treb. Thats 6000w per unit......me and my valves slunk off into the night and I never used power tetrodes again. But the mighty old 12AX7... still using it now.
And luvin it......oztules
