These blue glass Mullard made PM07 6AM6S EF91 (branded valvo) are a special quality British made early 1960’s, compatible with Little Dot headphone amps and tube buffers using the EF91 / 6AM6 / M8083 tube. The Mullard made 6AM6S have an extremely wide soundstage, low noise floor and are an excellent choice for the Little Dot amps. We have several hundred pcs in stock so as always extremely tight matching available. All tested on Amplitrex AT-1000. Enter qty 2 for matched pair. Just $23.99 each!