I use this lamp on a distortion pedal for Tube Works Real Tube. I simply removed the original lamp (still good) that I replaced with this one to see the differences:

With the Electro Harmonix 12AX7, the sound is more crystalline. One can adjust the distortion at a relatively low level without losing a lot of potato (beneficial use on a piece of rock or blues). When the effect is set up, the sound is very powerful.

However, at the equalizer, the medium's almost absent. It's a shame.