I tried that circuit, it's a pig to setup IE get the bias of the 12AT7 right, I discounted it and moved on. Having said that Fred Nachbaur knew his stuff, so up to you. Also after trying several times to get line stages with valves working properly I gave up and use a 5532 opamp tone stage in front of a valve amp or valve line stage, something like John Broskie's Constant current draw linestage, simple, easy to build.
There's a few tone controls using valves on the tinternet and they're all a right %^&* to get get working for one simple reason, valves run at high voltage low current, variable tone controls use pots, pots don't like high voltage on em so you have to use a lot of de-coupling caps, these introduce phase changes, phase changes introduce (potential) instability. So if you are not too experienced it can be "fun" getting the circuit's to work. I use the word fun ironically, my actual experience involves a lot more four letter words.
Think on, Andy.
PS, just to dishearten you further ECC81's/12AT7's like to oscillate, so throw one into a circuit with lot's of phase shifts, expect more "fun"
Here's what I built -
https://sound-au.com/project97.htm it can be configured for unity gain so you can put a valve linestage in front, Rod sells PCB's, I made my own, more hours of "fun". He lives in your neck of the woods, so no long shipping from the EU or USA. I bolted that onto this -
https://www.tubecad.com/2009/03/blog0161.htm he also sells PCB's ,though it's easy to build a point to point linestage. Here's some pics.