TUBE GAIN

I would check with Quicksilver first.

5751 are not drop in replacements for 12AX7 in all applications.

Indeed, it would be best to check with Quicksilver first. But keep in mind that some designers will object to you tampering with their perfection, despite the fact the swap will not damage the circuit. The two types are too similar for dire consequences to result (tubes have very loose tolerances anyway). The amp will simply not sound exactly as the designer intended it but, as the owner, which sound is better is for your ears and system to decide IMO. Just like rolling tube brands or sending your amp off to have mods done to it by a third party.

However, I do want to state for the record that using a 12AX7 in a circuit designed for 5751 is NOT a good idea. But the reverse is technically ok, if perhaps not subjectively so.

Arthur

THANKS I JUST REPLACED A 12ax7 WITH A 12at7 IN MY PHONO PREAMP AND THAT SEEMS TO DO THE TRICK.
YOGIBOY

IMO foget the 5751...NOS 1960s Mullard 7025!!!

I JUST PUT A SYLVANIA NOS 12AU7 IN AND IT IS THE BEST I HAVE HEARD YET.THIS TUBE WAS MADE IN 1952.HOW COULD SOMETHING THIS OLD OUTPERFORM ALL THE OTHERS I USED?