GEC KT8C / CV1079
The KT8C / CV1079 was based on the KT66 and is a fantastic sounding tube. Some people think these sound even better than the KT66 and similar to the Western Electric 350B. The anode is made of black plates shaped to increase surface area and radiate more heat. The base is a shiny white ceramic with B5 base pins and is able to withstand extremely high temperatures. The classic envelope is 47 mm in diameter. This is a great option to get the NOS KT66 sound at an affordable price.
If you don't want to re-solder your socket to use this tube, get the plug and play adapter here.