I'm hoping someone out there can help me choose a 5AR4 (or 5U4GB) rectifier tube to roll in my Modwright LS100. I have a 1960s NOS Amperex black base, but have the itch to look for something better. I've read some people rave about the Mullard metal base, but even I, as crazy as I can get chasing better sound, have to gulp many times before contemplating shelling out the $400-$500 those tubes now cost (let alone ever telling my wife!). I've also read that the Phillips/Mullard brown base (which may be labeled as CV1377) may be almost as good but at a much lower cost (though still not cheap - maybe $150-200). Finally, I read a reviewer say that the RCA 5U4G is a very good and inexpensive tube, but I think the LS100 would only accommodate the RCA 5U4GB (around $50).
BTW I'm using NOS RCA 6SN7 tubes in my LS100 and really like them a lot; just a bit of liquid warmth but without losing any details.
So, has anyone heard the Mullard metal base, the Phillips/Mullard brown base, or the RCA 5U4GB, either in the LS100 or any other model? And has anyone been able to compare any of those tubes to the NOS Amperex/Mullard black base?
Thanks for any help!