I replaced the stock tubes in my X7. First, I replaced the driver tubes with new old stocks (rca clear top 12AU7 and EH 12AX7), These definitely made a difference. Next, I bought a matched quad of Linlai KT-88 D tubes. In comparison to the stock power tubes they definitely tightened up the bass and the clarity of the midrange on my Klipschorns (vintage with Crites upgraded crossovers).

For the price, in my opinion they are a worthy upgrade and an alternative to Gold Lions.