Rummaging around in my valve box I have come across a pair of Mullard ECC88
I remember using these in an X-Box HPA
They are supposed to be a close pair and certainly produced much improved results
I do not have access to a tester so I do not know how much life they have.
Tom........... Yours to try for postage if you want
Lumley Heliosphere Audiomods 5
Voyd Valdi AN Arm 1 V2 and Denon MC
Audiomeca Talisman Highly Modded
Audiomeca Kreatura &,SW1X DAC1
Hovland HP200 MC
Hovland Radia
Ming Da 805 monos
Magnum Dynalab Etude, RWA Cassabria + LCD 3
Wilson Benesch Actors
Cables by Cardas, Hovland G3 and Yter