3683221.jpgPreamp Tube Gain Factor and Substitution Chart

12AX7 Family Tube Substitution

The 12AX7 family of dual-triode preamp tubes consists of the 12AX7, 5751, 12AT7, 12AY7, 12AV7 & 12AU7. These are all pin compatible with one another, the only differences being the gain factor of each tube. A common substitution is to replace a 12AX7 with a 5751 or a 12AY7 to tame a preamp that tends to overdrive too easily, allowing you to get a better ‘clean’ sound out of your amp.

Tube Gain Acceptable Substitutes
12AX7 100 5751 12AT7 12AY7
5751 70 12AX7 12AT7 12AY7
12AT7 60 5751 12AY7
12AY7 45 5751 12AT7 12AV7
12AV7 41 12AY7 12AU7
12AU7 19 12AV7

It is important to note that the above is not carved in stone and any of these tubes can be substituted for any other. For example in the 4×10 5F6-A Bassman the stock first gain preamp tube is designated as a 12AY7 which has a gain factor of 45. Replacing it with a 12AX7 that has a gain factor of 100 dramatically changes the tone and feel of the amp. Experiment and see what works best for you.