Preamp 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.
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