No other tubes can deliver vocals like the Blackburn Mullard's, and that's a fact. These B339 (the highest grade of ECC83/12AX7) tubes are extremely hard to find today and are becoming every serious audiophile's darling. And this pair also carries perhaps the "most British" label: Marconiphone!
Sound Qualities
The overall tonality of Mullard B339/ECC83 tubes is warm and lively with a very spacious sound stage. "Like a warm British jacket of the finest tweed, these glorious tubes have an attractive sweet warmth in their midrange and lower regions." This is how the experts on audiotubes.com describe the sound signature of British-made Mullard tubes. The top end is silky and pleasant and doesn't get rolled off. They retain a fine sense of "air" at the top, and the upper midrange is smooth and liquid. These tubes reproduce the human voice, especially female voices, with haunting realism. The British made Mullard tubes are also known to have an attractive sparkle at the top with rich bass...now we know where that "warm British jacket" comes from!
Appearance & cosmetic condition
Both tubes have nearly 100% of the paint and lettering remaining, and the close Blackburn date codes are perfectly visible:
B8I (B = Blackburn, 8 = 1958,I = September)
B9C (B = Blackburn, 9 = 1959,C = March)
Professional Tube Testing
NO short, leakage or gas. NO noise or microphonics.
Both tubes tested NOS ((100%+ of nominal mutual conductance) on a reliable Mercury 2000 tube tester with the following result (mutual conductance both in uMhos and in percentage of nominal):
Tube 1: 1,000/1,000(100%/100%)
Tube 2: 1,050/1,100(105%/110%)
Good tubes start at 650 and new tubes (incl. NOS/NIB) 1,000 - 1,050, and the Mercury 2000's rated mutual conductance (nominal) for new tubes is 1,000. Test result can also be seen in the pictures. In case you wonder what all these numbers mean to your sound experience, it's actually quite straightforward: mutual conductance directly translates to a tube's ability to amplify sound, so the higher the numbers the better.
