The 6922 tube type is probably the most used tube in high-end audio. There are many versions of this tube that have been made over the decades. The Mullard E188CC / 7308 tube is a high grade 6922 and a suitable upgrade in just about any compatible preamp.
These E188CC tubes were made in England at the Mitcham factory, somewhere around the mid '70's. They were produced for RTC in France and come in original white boxes with RTC markings. This tube's constructions details include dimpled top getter and gold plated pins.