The Mullard CV4004 / 12AX7 vacuum tube is well suited for guitar amps. Mullard CV4004 has short plate construction, thick glass bottle, and very tight assembly.
Mullard CV4004 / 12AX7 tube has an abundant amount of usable gain. This makes it very versatile. The tone of Mullard CV4004 resembles TungSol 12AX7, often described as vintage-like. When we A/B tested in our Marshall JCM, the Mullard CV4004 tube had a bit more thickness to the tone.
Best of all, the Mullard CV4004 showed no microphonic issues in fully cranked up Marshall. This makes Mullard CV4004 a reliable, worry-free choice for gigging.
If you are looking to re-tube your EL34 amp, the Mullard CV4004 is an excellent choice to go with the Mullard EL34. The smooth distortion of the Mullard CV4004 is a good match for the mid-range of Mullard EL34. The combination is versatile and works well, from crunchy rhythm work to solos.