I thought I'd give this subject it's own home so as not to clutter up Jules' Tube Rolling thread. Are these valves better known by another ident? I have two NOS Mullards ECC88's in the Delphonica Valhalla (I thought they were ECC83's until yesterday). I am planning to buy extra valves to cover me in case of random failures, but I don't think I will be buying Mullards as these fetch a pretty penny. What should I be looking for please fellas?