12at7 with 12ax7 tubes

Dropping a 12AT7 in for a 12AX7 does more than reduce gain. The cathode and plate resistors should be changed to make the 12AT7 operate in the most linear fashion. The two tubes have very different transconductance and plate resistance.

"The 12AT7 is interchangable with the 12AX7, but has slightly more than 30% less gain"

Rodman - I've heard that about the 12AX7 vs. the 5751, but never the 12AT7. Are you sure you're on track with this?

Sebrof- I guess I WAS off a bit. the 5751 is 30% reduction in gain. These sites have the difference as 40% less for the 12AT7: (http://thetubestore.com/gainfactor.html) (http://cydathria.com/fdm/12AX7_sub.html) and(to me at least)that seems greater than, "slightly more" of a difference(my bad). Both sites mention that the tubes are interchangable. The first site: that they are, "plate voltage compatible".

My thanks to all. I guess my question then is what Gmuffley is stating. I don't want to change components and don't want any damage to boot. I'll check the links given by Rodman99999 and go from there.

A follow up with the 12at7 tubes: I have a pair of Tungsram tubes that I brought for a VTL pre that was sold. I kept the tubes so hence the post. Installed them this afternoon (replaced a pair of Tungsol) and WOW. No difference in gain to my ears and the sonics of the Tungsrams walk all over the Tungsols. The battle of the T's should be the title of this post. : ) Thanks again to all.