For an Atlantic TRP, I got my close pair of GEC KT66's off eBay,. A UK vintage gear dealer with some old Quad amps NOS stock was selling them for about 89/99 GBP a few months back. Fantastic price, as they go these days. Should have bought a spare pair. Sound great, just as Fabio described. Mine were clear, but supposedly the grey glass ones sound a touch better, perhaps because they were military stock, hence the cream of the crop. In addition to looking at tube sites, especially UK ones -- PM me for a list -- watch HiFi Shark listings. Some UK tube dealers sell on ebay only. For a recti, I tried a number of well-reputed tubes, short of the highest end ones, and ended up with an Osram U50, which are not easy to find. Great clarity and a bit warmer than the rest.