Preamp Tube Gain and Compatibility Guide

All of the following tubes are interchangeable and may be used anywhere one of the other tubes was originally specified. The only possible exception is that 12AY7/6072As should be used only in circuits where the plate load resistor is rated for at least one watt.

Tube Number	Gain Factor	Comments
12AX7/12AX7A/7025/ECC83/CV4004	100	The ubiquitous guitar preamp tube
5751	70	Military 12AX7 with just slightly lower gain than a 12AX7. Less highs too. Great for cleaning up a harsh or overly bright sounding amp channel.
12AT7/ECC81/E81CC/CV4024	60	Fender reverb driver and phase inverter tube. Sometimes used to replace 12AX7s where lower gain and more note definition/clarity is desired.
12AY7/6072A	44	First gain stage tube in Fender tweed amps from the 1950s. More of the same effect as the 5751 above. Good for cleaner blues tones. Harp players like these to reduce feedback.
12AU7A/5963	20	Phase inverter in Vox amps. Sometimes used by harp players to reduce feedback in 12AX7 stages. Also a great substitution in 12AX7 type guitar distortion pedals. Allows for more usable range on the gain controls with less fuzzy/more bluesy distortion.