I just received the RCA JAN 832A tubes from vacuumtubes.net, replaced the FU-32s and listened for 3 hours. I have the Shuguang 12AX7M in the middle (like it better than the 50's GE 5751)
Did you clean the pins of the with RCA JAN 832A some jeweler's cloth to remove the black color (oxide) ?.
that black layer of oxide on the pins prevents the ideal performance of the tube, causing it to be immersed in the highs and dry in the low and mid, clean and listen to a big difference, greetings!
Initial Impression:
Compare to the FU-32s, the RCA 832A definitely gives better mid and treble resolution. The overall sound gives better sense of clarity. But the bass is definitely much weaker and loose. Leonard Cohen's vocal sounds 20 years younger. The RCA 832A also runs cooler compare to the FU-32, I suspect it will give less output power (it is common that Russia/Chinese copied power tubes usually can output higher current)
Depending on one's taste, can't really state the the RCA 832A is better than the FU-32 or vice versa. Please note that my amp is the "deluxe" version with larger power transformer which can better drive the FU-32s.
Will keep burning in those RCA 832A for another week and see if the bass will improve. Will also try pair the GE 5751 with it (but I already found the GE 5751 give loose bass, so might not be good combo with the 832A)