Valve phono stage

I have to wonder about the tubes you mention, specifically the ECC 801/12AT7 WA. Because WA is a suffix that was used I think by Phillips, and Phillips never made any ECC 801’s. At least so far as I know. Your tubes might legitimately be ECC 81s.  Real ECC 801, 802‘s, 803‘s and similar became very valuable in the last 20 years. The “0” in the 3 digit number indicates very low noise, tested by the factory.Therefore I would be skeptical about what it says on the box or on the tube, unless you know for sure the provenance of the tube. I have some Telefunken 12 AX7‘s and some Amperex bugle boy tubes that I bought back in the early 1970s. That’s the only reason  I feel sure they are for real. 

ECC 801s is the military grade Telefunken tube from Europe, one of the best ever made, very expensive. 801s is the same class as the ecc81, but the highest grade by Telefunken (long life, low microphonic).

12AT7 WA is Silvanya Gold Brand from the USA with gold pins, it’s a bargain, great tube

Another favorite of mine was Matsushita pinched tails 12at7WA - very rare. Mullard made tube factory for Matsushita in Japan as far as i know.

None of the mentioned above were made by Philips

12AT7 (12AT7WA) = ECC81 (ECC801s)

So which valves would be a suitable & significant upgrade from the stock ones in the Herron?

Chakster, It seems you repeated back to me exactly what I said to you; an ECC801 is not likely also to bear the stamp "12AT7WA".  Apparently we agree on that, and we agree that REAL ECC801s/802s/803s are very rare and very valuable in the crazy tube collector market.  If yours are real, good for you.  I do have some real Telefunken ECC83/12AX7s, and I only know they are real because I bought them in the 70s, from a reputable source, before this craziness began and before the Chinese and Eastern Europeans started making bogus TFKs and Amperex and etc tubes.  And they do sound great, although I only own one piece of gear that uses 12AX7s, a vintage Quicksilver full function phono preamplifier (highly recommended and an amazing bargain, if you can find one for under $1200) which I use for back-up to my Steelhead, on my basement system.  Can't use it on my upstairs system, which is all balanced/Atma-sphere and anyway has no 12AX7s in circuit.

Infection, If you choose to purchase the Herron, I strongly advise you to run it with the tubes that Keith Herron has chosen for it.  If you cannot resist the business of tube rolling, at least wait a year or so until you have a real idea of the sound of your Herron, so you'll know if substitute tubes make a favorable difference or not.  In purchasing the Herron, you would be paying a rather high price for a conventional single-ended design; the justification for that is you are paying for the undeniable expertise of Keith Herron in the bargain.  I would guess he has been very careful in selecting what tubes sound best in his circuit.

@infection I mentioned earlier about how you can't just buy tubes off the shelf and expect them to work in a high performance circuit.
Lew's advice is good- those tubes are in there for a reason. This isn't saying that you can't do better- you can, just expect that when you buy a hot-shot tube be it boutique or NOS, that it may not be as quiet or low microphonics as you expected and you may have to return it and try again.

We buy tubes 100 at a time, so we have more examples to go through to find the tubes in the box that sound right. I'm sure that's what Keith is doing too.