A pair of factory-matched premium "Black Bottle" Treasure 6CA7-Z Valves from the Shuguang factory in China.

(Auction is for TWO Valves.)

The 6CA7-Z can be used in place of the EL-34 valves

These have been highly praised in the Hi Fi press and online forums.
A bit of searching will reveal great enthusiasm for these black beauties!

http://www.enjoythemusic.com/magazine/equipment/0509/shuguang

_treasure_series_6CA7_kt88.htm

At last a viable new alternative to NOS valves.

Fairly long run in time of 300 hours for them to be revealed at their best.

I have several pairs so matched quads are available.