How to tell.....

Dear tube experts,

How to tell a TFK diamond bottom smooth plate tube is a 12au7 or 12ax7 if most of the letters are missing?

Thanks!

eugeneli10-17-2006 9:15pm

reb1208 Details Discussions Posts This discussion Message User 518 posts 10-18-2006 at 01:50am Copy Comment URL Report Comment Edit Delete You could listen to the tube. The 12AX7 will have higher gain.
boa2 Details Discussions Posts This discussion Message User 1,551 posts 10-18-2006 at 02:47am Copy Comment URL Report Comment Edit Delete You could listen to the tube. The 12AX7 will have higher gain. Are you sure these tubes are interchangeable without consequence? I thought not, but I could be wrong.
amandarae Details Discussions Posts This discussion Message User 512 posts 10-18-2006 at 04:13am Copy Comment URL Report Comment Edit Delete You need a tester.