Most people have heard of the famous GEC KT88, which has become known as the best sounding KT88 ever made. It is known for a smooth but extended treble, warm but accurate mid-range, and thunderous bottom end. It’s fame has caused this tube to become nearly impossible to find. However most do not know about the GEC TT21. The TT21 is a GEC KT88 with a top cap and a re-enforced plate structure capable of handling bursts of 1000 volts on the plates. Having owned and compared the GEC KT88 and the GEC TT21 side by side, they sound exactly the same and in my experience the TT21 has lasted longer due to the re-enforced plate structure. We have several pairs and one matched quad available, all tubes are new old stock. There may be some variations in silk screening and boxes, and please be aware that GEC burns these tubes in at the factory, so some stickers may appear to be burnt.
All tubes come with adapters so they can be used in place of a standard KT88.
All tubes are tested on a AT1000 computerized tube tester at real world operating voltages (450 volts in the case of the TT21), one tested tubes are also matched at those voltages. For power tubes we match based on EM first and then GM. For small signal tubes we match based on GM then EM.
Please be aware that vintage vacuum tubes are antiques and carry no guarantee or warranty. We provide a sheet explaining what you purchased, your test results for your tubes, and if need be can provide photographs of the tube on the tube tester before we pack and ship them.