Mullard 5AR4 tube. f31 means it's from 1958 to 1962. The X8E means it was made in at the Sittard plant in Holland. A rare and highly sort after tube. I purchased this as a NOS and put 150 hours on it. They last for 10,000 hours. Comes with Mullard box. $149 plus shipping. I can take paypal. Please check my feedback on Audiogon under mikeg. I sold the unit this was used in.
