I want to know the difference between 12AX7 tubes and 12AT7 tubes. I know that both are triode preamplifier tubes.
I'm asking this because I own preamplifier who use both tubes. The difference is 12AX7 is for phono channel and 12AT7 is for main channel.
Since I want to replace with mullard tubes, should I change both or just 12AT7 because I didn't use phono.