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12au7 or 12ax7

I recently purchased my first tube amp a Primaluna Prolouge 5, the previous owner said the tubes were at the end of their life. I replaced the factory KT-88's with Tung-Sol KT-120' with which I am very pleased. My questions is which would give me the biggest sonic benefit replacing the 12au7 or the 12ax7? Both will be replaced in time which do you think I should do first?
lardawg

Showing 2 responses by atmasphere

atmasphere's avatar
atmasphere
11,634 posts
 
@wolf_garcia , be careful with those gold-plated tube sockets! Gold is soft and so the socket won't survive many tube changes before the plating fails. When that happens the raw copper beneath is exposed and the socket contacts will turn black.

IMO/IME, you are far better off with tin-plated sockets, as tin does not want to corrode (similar to gold in that regard) but its much harder, and so the socket can survive for decades of use.
atmasphere's avatar
atmasphere
11,634 posts
 
The 12AX7 is the voltage amplifier in the amp

The 12AU7 is the driver tube

The 12AX7, being upstream, will have the most sonic merit. The best made were Telefunken but are nearly impossible to find NOS at this point. So if you're rolling tubes, this is the place to start. Keep in mind though that the 12AU7 is going to effect things too- whatever you hear from the 12AX7 will be passing through the 12AU7.

What I always tell my customers- have at it, have fun, and don't drive yourself off the deep end.
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