This is a vertical deflection pentode for color TVs. It has the 12 pin "Compactron" base, all glass construction, and does not include a top cap connection. The rated PD= 19W. With a modest voltage, a PP pair can give 34W, and with an estimated h3= 3.57%. This would put it in the same category as the 6L6-oids, so far as operating voltages and power output. As for how this actually sounds, that depends on the harmonic "personality" of the distortion. If it's mainly h3, then it won't require any extra help from local NFB: just add enough gNFB to take the "edge" off, and, of course, to improve speaker damping. As with the horizontal deflection types (and the 6L6-oids) the screen voltage rating is limited. This makes UL difficult to implement without OPTs with special tertiary windings. Should local NFB be necessary, it can always be implemented as cathode feedback, or parallel feedback. A stiff (preferably active regulation) Lo-Z screen supply is best for sonic performance. Being that this is a vertical deflection type intended for developing max RMS power, the ratings are on the conservative side. With a bit of spec busting, you can run it hotter than rated, as audio final use is far less demanding. This will get you closer to Class A, and reduces x-over distortion.
It does, however, like a heavier load: 5K44 (P-2-P). The heavier cathode gives the 10JA5 a higher current capability than usual for audio finals. This can help the sonics, especially bass-heavy material. If there's a drawback, it's the odd heater voltage: 10.5V. This being due to the use of series strings operating directly from the AC mains for heater power. It will require an extra heater PTX for that reason.
The 10JA5 looks to be another audio "sleeper", in that audio final use isn't mentioned in the spec sheet. Of course, this isn't a type you'd use in Class A anyway. As with most of these TV tubes, the most linear portion of the plate characteristic is well within red plate territory.
For a 30+ WPC stereo, it's one to consider.
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