Phase Inverter Substitution

OLAF MELCHER · July 1st, 2007, 05:38 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 ?

Thanks

zook · July 1st, 2007, 07:16 AM

yes you can it provides more gain and earlier breakup

Winnie

EMan · July 1st, 2007, 08:07 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.

nonvintage · July 1st, 2007, 10:27 PM

You might want to try a 5751 also. A little less drive than a 12ax7 and a little more than a 12at7.

July 1st, 2007, 05:38 AM	#1 (permalink)
OLAF MELCHER TDPRI Member Join Date: Feb 2005 Location: Western France Age: 47 Posts: 55	Phase Inverter Substitution 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 ? Thanks __________________ jazzjoker

July 1st, 2007, 07:16 AM	#2 (permalink)
zook Tele-Holic Join Date: Aug 2003 Location: Northeast Kingdom, Vermont Posts: 782	yes you can it provides more gain and earlier breakup Winnie __________________ I have noticed that happy people are often evaluating themselves and unhappy people are always evaluating others. -William Glasser

July 1st, 2007, 08:07 AM	#3 (permalink)
EMan Tele-Holic Join Date: Apr 2003 Location: Dallas, Texas Posts: 939	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, 10:27 PM	#4 (permalink)
nonvintage Tele-Meister Join Date: Mar 2006 Location: San Diego Posts: 464	You might want to try a 5751 also. A little less drive than a 12ax7 and a little more than a 12at7.