Maybe paralleling tubes can get you there? I honestly don't know where I found this very simple schematic, but its been on my list of things to breadboard for a while since I literally have all the parts already. Not sure how much wattage is here. 12W6, 25L6 tubes are cheap and can sound great. Seems like a good beginner project which is where I'm at too.
For that power level unless you're married to triode and feedback phobic consider single ended pentode mode output. Just finished measuring up a 6SF5/7591 that delivers near 7 watts under 1% thd from a 19 watt final. The oscilloscope shows negative peaks hitting 9 watts, positive peaks near 25. A beefier final in the GU 50 range might get you close to that 15 watt continuous power number.
How about design a power buffer using mosfet OPS and drive it with a 6DJ in plate load then cathode follower?
Low voltages, good tube, gain of about 25dB with bypassed plate loaded section, and glorious sound quality.......
HD
Low voltages, good tube, gain of about 25dB with bypassed plate loaded section, and glorious sound quality.......
HD
You could just put a HV current mirror under the cathode of your favorite output tube (current combined with the plate) to get twice the power and half the output impedance. (OT changed to lower Z then)
Use a LV bipolar current mirror with a HV Mosfet cascode above it's output to get the HV current mirror. Has to handle the more than 2x B+ the tube plate swings up to.
With a matched pair of 6C4C in parallel and the current mirror, you could get 4X the power, 14 Watts of clean power using a 1.25K SE OT like Edcor or Hammond or Toroidy.
Use a LV bipolar current mirror with a HV Mosfet cascode above it's output to get the HV current mirror. Has to handle the more than 2x B+ the tube plate swings up to.
With a matched pair of 6C4C in parallel and the current mirror, you could get 4X the power, 14 Watts of clean power using a 1.25K SE OT like Edcor or Hammond or Toroidy.
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Cheapest but still very good PSE is a pair of 4P1L. Plenty of information on Ale Moglia's site Bartola Valves. I ran that for a couple of years and so did Ale. Good thing is the 4P1L has a gain of 11 so you can drive it with a 2P29L and get a 2 stage all-DHT SE amp. Simple, elegant and would sound very good indeed. Both stages in filament bias with Rod Coleman regs.
You Lucky, Lucky Bastard 🙂
Found a link I was looking for: the original article on using PA transformers https://ozvalveamps.org/optrans.htm including wiring diagrams
It all comes down to three questions: how much of a hurry am I in?; how much is my time worth?; and How fast do I want to spend?
A single triode wired 6W6 into a 5K OPT in an SSE board gave me 2 to 2.5 watts depending on B+ voltage. Two in parallel into half the load impedance should make twice the power, 4 to 5 watts. The 6W6, 6DG6GT, 12W6, 12L6, 25W6, 25L6, and 50L6 are all the same except for the heater voltage.
My favorite small tube SE amp is a triode wired 6V6GT in an SSE board on about 325 volts of B+. It makes about 2 watts and sounds very close to a 45 DHT tube in a TSE. 6V6GT's have become pricey, but 5V6GT's and 12V6GT's can still be found for $5 each.
I just thought that for the most part of the tube-hifi history the pentode output was the most common. So if I want to capture the feeling of how it worked and sounded like in the past I should look for pentode sound instead.
You could easily try all three topologies in the same Amp, triode strapped, ultralinear pentode or regular pentode, just by moving the position of the screen grid connection. Maybe start out with the Tubelab circuit or board.