I had been lucky enough to find 4 of these used on line and thought I would give them a try. I had originally put them in my Jet City 50H along with one Tungsol with awesome results. So on a whim I decided to pull 2 out and throw into my Marshall DSL40C in V2 and V3 with 2 Tungsol's in V1 and V4. All I can say is they absolutely changed the sound of the Marshall for the better and it was good before with 4 Tungsol 12AX7's in it. Much more musical now, warmer, and smoother sounding. There is even less hiss on the red channel where I generally keep it at. I ended up ordering 2 more so I can throw them back in the Jet city. DO NOT HESITATE TO BUY THESE, GREAT TUBES!!!!! Now I cant wait to get the 2 I ordered along with the Preferred Series EL34's I order to put in the Marshall also.