Build the circlotron if you want to, but be prepared for the potential problems along the way.
The first thing I notice about your schematic is that there are not individual resistors in each 6AS7 cathode for current sharing, that is asking for one or more tubes to take over, and destroy itself.
Don't get me wrong, OTL tube amps can be very nice, depending on the design, and the factors you are willing to trade off.
How many Ohms are your loudspeakers?
Not just the manufacturer's nominal rating, but the impedance minimum(s) at various frequencies. A typical 8 Ohm loudspeaker may have minimum impedance(s) of 4 Ohms.
10 Watts rms into 8 Ohms requires 1.58 Amps peak.
10 Watts rms into 4 Ohms requires 2.24 Amps peak.
That is a lot of current from 12 cathodes of 6 6AS7 in series with 12 more cathodes of 6 6AS7 tubes.
OTL and circlotron requires many output tubes. The cathode impedance of a 6AS7 is 143 Ohms, for 12 cathodes (6 tubes), the cathodes are 12 Ohms. The circlotron schematic you linked to has 12 Ohm + 12 Ohm output impedance = 24 Ohm impedance. That is because the set of 6 tubes is in series with the other set of 6 tubes.
For an 8 Ohm loudspeaker, the signal will be developed across 12 Ohms cathodes, + 8 Ohms, speaker + 12 Ohms cathodes.
If there is 10 Watts into 8 Ohms, the signal power distribution will be thus:
8 Ohm loudspeaker 10 Watts
24 Ohm tube cathodes impedance 30 Watts
Of course there is much much more total power dissipated in the tubes (the plate dissipation), I just listed the signal power dissipated in the amplifiers output impedance.
The damping factor of 24 Ohms output impedance into 8 Ohm loudspeaker is 0.33 (yes, the damping factor is less than unity). The frequency response is almost entirely dependent on the loudspeaker impedance versus frequency.
Negative feedback (that does not exist in your schematic) could reduce the output impedance, but there would still be the same total power dissipated in the tubes.
The circlotron amp is very inefficient at providing power to the speaker, but is very efficient at heating the room.
A tube amp that drives an output transformer from the plates is more efficient than your schematic.
For a 10 Watt tube amp that can work with a variety of loudspeaker impedances (both nominal and minimum, an output transformer is a very practical thing.
A PSE 300B amp (Parallel Single Ended) could easily put out 14 Watts.
A typical damping factor of a 300B amp could be 3.3.
That is 10 times better damping factor than the schematic you posted.
Is your budget a concern?
