OK, so I've had my new Mullard KT88 tubes in my amplifier for a little less than a month now and have listened for probably a couple dozen hours or so, mostly in two hours stretches or thereabouts.  So it's time to report back.

This is just a listening evaluation without measurements, and that's something I normally don't do.  That said, take this post for what it is.  Total seat of the pants observation.

So far, I think I like these tubes.  They are somewhere between the Tung-Sol 6550 and the Electro-Harmonix 6550 in the range of smoothness.  Neither of those tubes lack smoothness, but the EH sounds a little more detailed and the TS sounds a little more laid-back.  The Mullard KT88 is sort of in-between.

To be honest, I am interested also in the longevity of these Mullards in my Audio Note Kit 2.  I think I may have mentioned this here or in another thread, but just in case I hadn't, I find that KT88 tubes don't last as long as 6550 tubes.  They don't fail right out of the box, but they do seem to have a shorter lifespan.  We'll see on these.

They do sound nice though.  Time will tell if they get to be "regular stock" tubes for me like the Tung-Sols and the Electro-Harmonix.