Well, the Jadis was actually bought in 1999. But, I would say the sound peaked in the 3 - 4 month area. After that, I didn't perceive things improving.
Interestingly enough, I retubed the amplifier early this year, when I sold it, and it leapt forward tremendously. To the point, where I went from one end of the spectrum to the other - from buyer's regret to seller's regret. But, since then, I have picked up another Jadis, one step higher. Though, in many ways, it has yet to equal the former amp.