I had a Telefunken 12ax7 tube go out on me in the V4 (R) position of my Aesthetix Rhea, so I replaced the pair with stock Sovtek 12ax7WBs. Do I need to replace the Teles with a matched pair, or can I just pick up a single and throw it in. You can also use 12AT7 (ECC801s) instead of 12AX7 , military Telefunken tubes (if they are not fake) are much better than Russian Sovtek or any other new tubes. |
You can "use" a 12AT7 to replace a 12AX7, in that the pin connections of the two tube types are identical, but that would be far from ideal. The 12AT7 has less gain, a lower plate resistance, and a higher transconductance compared to a 12AX7. In a phono stage, the difference in gain would be quite noticeable, even with high output cartridges, if one were to replace a 12AX7 at the phono input with a 12AT7. But also the 12AT7 would function suboptimally in a circuit designed for a 12AX7, so there might also be noticeable distortion. (I am qualifying my statements, because I know someone is going to claim that he used a 12AT7 in this fashion and it sounded wonderful.)
I know it works perfectly and a person who replaced 12AX7 with 12AT7 in his new Mac preamp noticed huge upgrade in sound and (no problem with gain). They are in use ever since for more than one year for everyday listening sessions as far as I know. German military NOS telefunken are superior to any Russian tubes. My advice to OP is to stay with NOS Telefunken tubes (...ax7 or ...at7), matched pairs! |
