Tubes for EAR 834L and 834P?

I do not have this amp but I would try Mullard box plate 12AU7 from the 70's or even better the mid 60's. I would also look at the GE, JG 5751 NOS [sub for 12AX7] black plate with copper grid posts made in 1956 or 1957 these are sweet nice tube but 2 or 3 Db's less gain than the 12AX7 I just love these tubes , you could also try a Telefunken 12AX7 smooth plate NOS I like these better than the ribbed plate Telefunken just My thoughts good luck some people like the RCA clear top for 12AU7 but have not tried these Myself, Brimar would be a place to look at also very nice tubes not to much money.

i'm running yugo 12ax7 (nickel plate) and yugo 12au7s. try them first, their cheap and have very clean highs.

I have tried NOS RCA and Sylvania 5751s I got as spares for a Joule Electra preamp in my 834P. Not enough gain. Have been happy with the EIs that it came with and have also had good sound from Teslas although they got a bit noisy after a few months. Tubes should last a long time in the EAR.