I have listened to them at length, and the bass is not as full, or powerful, as the NOS TungSol's, and the dynamics, are not as good. Overall, they are closer in sonics than any other current production 6550(IMHO). The thing about new production tubes, is that they just don't last as long as NOS tubes. I checked the amps when the tubes were new, and they were putting out 58 watts(a push-pull pair). A month later, they could only manage 42 watts.I tested them again, three months of use, and they were putting out 38watts. My 3 year old TungSols, still put out 47 watts. If your amps are not putting out much over 500v, on the plates, the new TungSols should be good for about a year, or so.
