Phase Inverter Substitution

July 1st, 2007, 06:38 AM
Hi guys,

does anybody know if one can safely substitute a 12AT7 tuby by a 12AX7 tube in SF Vibrolux Reverb and SF Super Reverbs without damaging the amp ?


July 1st, 2007, 08:16 AM
yes you can it provides more gain and earlier breakup


July 1st, 2007, 09:07 AM
12AT7 tubes have a lower effective plate resistance than a 12AX7.

If you run your amp bias 'hot' ( like a lot of folks tend to do ), the amp may be running the output tube grid(s) positive. With lower available plate current via the 12AX7, it will have less ability to drive the output tube(s).

A 12AX7 can also, for the same reason, make it harder for the output tube grid to 'unload' possibly contributing to blocking distortion.

Will the substitution hurt anything....as mentioned above, nope.

July 1st, 2007, 11:27 PM
You might want to try a 5751 also. A little less drive than a 12ax7 and a little more than a 12at7.