274b Rectifier tube
I recently had a DHT preamplifier built and choice of 5U4G or 274B. This 274B rectifier tube is a great tube for the money it has a nice smooth balance. Adds nice depth and very stable expanded soundstage. Very close to the Sophia in quality for far less money. To get noticeably better you would have to buy the Emission Labs 274, but is expensive.