12AX7A vs 12AX7

Da ugoloso Ven 17 Feb 2012 - 8:37

Salve,
ho notato che negli USA si trovano più valvole 12AX7A che 12AX7, chiedevo
se ci fosse molta differenza tra le due, anche in termini di ascolto.
Grazie

Da pilovis Ven 17 Feb 2012 - 11:46

ugoloso ha scritto:Salve,
ho notato che negli USA si trovano più valvole 12AX7A che 12AX7, chiedevo
se ci fosse molta differenza tra le due, anche in termini di ascolto.
Grazie

Trovato in rete:

12AX7: the original version of this tube, released in 1947. This can only be used in parallel filament circuits. This is not a big deal as virtually all audio equipment is of a parallel filament design. In other words, these will work fine in a Marshall.

12AX7A: This version can be used in series or parallel filament circuits. These usually date to the 1960s and have gray or black plates. Vintage versions of these are about the most sought after tubes of any type today. Sometimes, 12AX7A tubes made for the US Military are labeled 12AX7WA. DO NOT confuse these with current production Sovtek or Chinese crap with the suffix WX, WB, or WC! These are not military tubes and are not NOS tubes at all.

Also, as tube manufacturing became refined, the 12AX7A became much quieter. So much in fact that a lot of 12AX7A's were labeled 7025's (a very quiet version of the 12AX7).

So the bottom line is that you can use either of these tubes in your Marshall amp. It's just that an NOS 12AX7A tube is considered to be premium over the 12AX7.