My Vox VT40+ sound pretty darn good as it was but I was used to NOS tubes in my tube amps and the difference they make. I found how my Vox sounded with an RCA 5751 I have in my box-o-tubes but with a loss of gain. The cleans and the Fxes were dripping with cream with that tube so I gotta get a vintage 12ax7 with the gain and the cream. I emailed a tube vendor because he has some good tubes with good prices for a suggestion for my amp. He sent me a link to a British Mullard branded as an RCA for $40 after he slashed the prices from $80 because he's got a good stock of them now. I ordered it. I got the tube today and it exactly what he said it is. It is so sweet that it's unreal and this amp sounded better than my tube amps. Vox really has the technology with the Valvetronix system that works. The cleans are creamy and the heavy metal are like gravy. Just one tube.