OK... so tell me about 12AX7's

[Tony L]

Good ECCxx valves last pretty much indefinitely IME. I’ve got a used trio of 1960 Blackburn Mullards in my Verdier preamp’s phono stage. They’ve been in there about a decade now, in daily use (being a standard preamp the phono stage is powered even if I’m listening to CD/digital). I test them every year and they are all still strong, and I’ve no idea how much use they had previously (one pair came with my old Stereo 20, the other pulled from something else, I can’t remember what, maybe a Ferrograph mono R2R). All sound great. That set will likely outlive me!

 

[les24preludes]

I have loads of 12AX7 tubes, about half tested. Includes 2 nice Amperex ones and several Mullards, though not closely balanced. I'll be selling all of them. I'll make a list and post it. Open to PMs. Andy

I've made a list which I will put in the classified. There's some test data at gm=1.6 as per AVO manual, but it looks a bit like the tubes were tested in circuit and the anode voltages marked down for each half. Going by the markings on the boxes the "new" voltage looks like it was 60V. There's one where "new" looks like 100 but that must have been a different circuit. These were tested over 10 years ago and I can't remember how they were tested. Here's what I have

CV4004 KB/D 50/48 very good
GPO KB/DA CV492 original box NIB
Amperex 12AX7A "good" red print, clean
Amperex 12AX7A red box red print, clean
Mullard GB ECC83 38/30 @ 1.6gm marked good
Mullard GB ECC83 43/57 @ 1.6gm marked very good
Mullard CV4004 44/38 @ 1.6gm marked very good
Mullard GB ECC83 ?
Mullard 20/22
Mullard GB ECC83 44/50 @ 1.6gm. marked very good
Mullard GB ECC83 44/56 @ 1.6gm. marked very good
GEC 56/44
GEC marked "OK"
GEC 50/25
GEC 43/48
GEC 60/58 very good
Brimar ?
Brimar 38/44 very good
Brimar 32/48
Japan ECC83 62/44
Bugera 12AX7C Premium Selected
? 12AX7S 104/96 excellent
Dynaco 62/56 very good
White Star logo ECC83 marked P6WN?
Marked "ECC83"
?mullard 54/50 very good
? ECC83 74/60. print erased
? ECC83 68/54 @ 1.6gm. "strong"
? green print erased
? print erased