I have the Audio note M5, preamp and i changed tho original tubes (sounded very woolly) in Telefunken . What a difference !! I suggest: Telefunken,Siemens,Phillips,RCA
pre amp tubes
Are 12AX7 and 12AU7 tubes interchangeable in preamps and if so what are the differences. Any suggestions for not overly expensive tubes? I have used RCA nos and Tungram before but can I do better?