I don't think ECL86's are appropriate in this circuit. Get some 6P15P-EV or SV83's.

No wonder; the amp is designed around the 6P15P-EV

I prefer solid state rectification from a pair of 1n4007 diodes to the rectifier tube.  The Zkit1 uses this form of rectification.  It yields higher voltage out and slightly more power.  I think it adds more punch to the sound, or a crisper , more detailed sound.  I've experienced no problems from the solid state rectification...some say that the fast turn on is hard on tubes, but I've seen none of that.  You can make a solid state rectifier out of an old rectifier tube...just break the glass, be sure to cut the heater wire or just let it burn up, and solder a couple 1n4007 diodes to the appropriate pins, diode anodes (no band) to tube plates, diode cathodes (band) to tube filament pins (cathodes).

Dan

Once again my thanks to those that have made suggestions. I'm getting close now I reckon, and I'm getting used to the SE84ZS 'sound'. It's certainly winning in the 'tuneful bass' category, and that bass is going as deep as I need it to go (one crucial factor for me). The Audion is still ahead in various of the "S" categories however: soundtage, separation, smoothness... but it's a close-run thing.

The Fullmusic 300B/c in my Audion that look down on the SE84ZS snorted with derision when dank suggested that a $2 power tube was the best I could do (the Fullmusics cost someone over $400) but he has a point and as has been stated above the circuit was designed around the 6P15P-EV.

One slight minus point that I won't be able to solve with valve rolling is the max volume available. I'm frequently listening at top volume, and whilst that's perfectly delicious and satisfying there are isolated occasions when I just want a little more. Which is one reason why I may end up keeping both amps for the time being.