I recently purchased two, brand new, matched quads of JJ/Tesla KT88 from an authorized dealer. I tried them out for a maximum of 30 hours in my Rogue M180 monoblock amplifiers, but I still prefer the factory Rogue tubes (KT120). These KT88 operate fine, hold their bias, and still measure as new in my Hickok 752 tube tester (based on Gm and absence of leaks). I'd prefer to sell the entire octet, but can sell as two quads (though not as pairs). List price is for one quad (four matched tubes).