IMO, that schematic leaves a lot to be desired. The 470 Kohm I/O grid to ground resistance will interact with the CMiller of the triode to roll HF info off. 
Also, it's a paraphase, not a LTP, configuration. A high RP/low gm type, like the 6SL7, should be used only with pentode mode "finals", IMO.
"Fixed" bias could be trouble, given the lowish grid to ground resistance limit. You could buffer the driving triode's plates with DC coupled ZVN0545A source followers, to get around that problem.
Also, it's a paraphase, not a LTP, configuration. A high RP/low gm type, like the 6SL7, should be used only with pentode mode "finals", IMO."Fixed" bias could be trouble, given the lowish grid to ground resistance limit. You could buffer the driving triode's plates with DC coupled ZVN0545A source followers, to get around that problem.
Yup. Like I said, I'm not building it as shown. I can't stand paraphase, and it will be super easy to simply do some creative jumpering to do it up as a regular LTP, run a CCS off board, and do it up as pentode mode with NFB to the grid of the other triode in the LTP. Easy peasy, and I have thought about the source followers for fixed bias too, although simple cathode bias would even do fine for its intended use. It'll be a neat little project.
Thank you for your clarification. You are correct. A higher power SE amp would be fine. Of course high power is relative but something like 30+ watts similar to a ST-70 seems to be about the lower end of power for my needs.
If the power supply is very robust a lower power maybe be fine as well.
Thank you Kevin. My current speakers are Stirling Broadcast LS3/5a V2. They are low efficiency at about 83dB/1watt/1m. The are 11ohm nominal so are not hard on amps.
I also run a clone of them but they are more efficient.
I had success on Dynaco St-70 power and great success on quad EL-84 monoblocks. Both around 35 watts I believe.
They should (IMO) be connected to 8 Ω speaker taps and, therefore, be derated to 81 dB. sensitive. Paul Joppa has provided us with a rule for mating speakers and amps. Joppa's Rule states that for "typical" listening spaces, an amp/speaker combo should be capable of producing 102 dB. SPL peaks. Applying that rule to 81 dB. sensitive yields 64 WPC. That's PP KT88 "territory".
That may be true but my previous VTL tiny triodes were 45w in tetrode and 25 in triode and both modes were plenty powerful and were a great match. Would more power be better? Maybe but not necessarily. I also use the VTL it-85 integrated and it was 4 x EL-34 and 60w. It did not have the same magic.
IMO, that schematic leaves a lot to be desired. The 470 Kohm I/O grid to ground resistance will interact with the CMiller of the triode to roll HF info off.
"Fixed" bias could be trouble, given the lowish grid to ground resistance limit. You could buffer the driving triode's plates with DC coupled ZVN0545A source followers, to get around that problem.
As a followup to this, here is the tentative schematic for the planned use of the board I ordered. This should be a very easy set of simple modifications, and with a small separate PCB for the CCS circuits it should still be pretty compact. Some simple creative jumpering should be all it needs.
This assumes a 300 volt supply after filtering, and maybe a hair less for the screens (S+) that has an additional filter stage, with something like a 12 volt or so negative rail for the CCS. Probably doing a BJT CCS like Sy used in the Heretical Preamp design.
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I suppose I could, I might even have a few around here somewhere. Could even cascode it with a bipolar for better performance. I forget how they perform naked as far as effective impedance, but for something like this they would work. I think they need about a volt minimum so would still need a small negative rail, which is no big deal.
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