We have matched quads in-stock, ready to ship.
This is the KR Audio KT88. Specify when ordering if you need matched pairs, quads, etc... This is a replacement for any KT88 tube. If you would like to upgrade your Opus 4 to KR KT88s, please contact us during the order process.
KR Audio offers a six month warranty on all tubes from the date they arrive at wholesaler or the date they are installed in an OEM amplifier.