5AR4 rectifier tubes - Chinese or Russian?

A third knod to Mullard / Blackburn NOS. Expensive, but worth it and will likely last long. Buy from a reputable seller, like Upscale, Vintage or The Tube Store. A rebranded Mullard should be $75-85/tube last time I checked and could be branded as Amperex, RCA, GE or some other companies that had Mullard make their tubes. Mullard branded tubes (labeled "Mullard") will run more expensive so I'd look for the rebranded ones from a reliable seller. Same tube with a different label. Best versions of the 5AR4 are actually metal-based versions but those will cost your first-born, and I'm not sure are worth the added premium (I guess that depends on how much you love your child). If you'd prefer to hang onto your heir apparent you could seek out an NOS 22S22C substitute, for which your soul may be adequate payment. Worth it for the extra bottom end resolution and bragging rights.

By the way, Kevin Deal said he'd spend his money on the 12AU7s and 12AX7s and not worry about expensive rectifiers,

Kevin knows what he's talking about and I would pay attention if I were you. Prima Luna are his product line and he knows them as good as anyone. People here probably responded to your query the way they did because of the way you stated your question.

12AX7's - I really liked Tungsrams in another application (a different amp), which can be find re-labled as Amperex. I haven't had much experience with 12AU7's so could not comment.