Of all those tubes mentioned in this, by far the best sound I got was from the white box "Mil Spec GE-6550" with the green label, interesting was the glass was inert because it was twice the thickness of any other tube.
https://img.ruten.com.tw/s2/c/d2/58/21544929147480_714.jpg
Still available, not cheap.
http://yahoo.aleado.com/lot?auctionID=e215700969
http://www.worthpoint.com/worthopedia/ge-6550a-jan-quad-set-green-169377351
Cheers George
https://img.ruten.com.tw/s2/c/d2/58/21544929147480_714.jpg
Still available, not cheap.
http://yahoo.aleado.com/lot?auctionID=e215700969
http://www.worthpoint.com/worthopedia/ge-6550a-jan-quad-set-green-169377351
Cheers George