This Mullard CV4004 / 12AX7 Reissue looks nothing like Mullard tubes of old but it has a lot to offer. This is a small plate design more suited to high gain amps. Old Mullard with large plate structures are sought after for audio systems because of their gain and detail. Those same attributes are the last thing you want in your Marshall stack.
The smaller plate reduces noise. They are dead quiet both electrically and mechanically. Nice thick bottles and well aligned internals also help. If you currently like the Tungsol 12AX7 you will love this tube. The gain is similar but overall it is quieter and a bit warmer to my ears.