Absolutely beautiful 1956 Mullard "Shield" 12AX7/ECC-83, made in the famous Blackburn Plant. Tube tests good at 1600/1650 Gm versus a minimum of 1000 Gm for my Triplett 3444 tester. Tube labelling is absolutely pristine, everything is clearly legible including the mC1 and the "B6B" which signifies 1956 manufacture in the Blackburn plant. Construction is long grey plates with a dual post mounted rectangular getter. The tube has the characteristic Mullard parting lines on the glass envelope and gives the characteristic "flash" when the filaments are first lit up. I played the tube in my personal stereo, it sounded fantastic, no hum or microphonics.  I have all different preamp brands in my collection, but typically run a pair of Mullard mC1's because they really live up to their great sounding reputation. I get lots of compliments on tube quality, accurate description, good packaging, and fast shipping, see my feedback if interested. This tube will be double boxed  to protect it while on the way to you. Good  luck bidding on this wonderful Mullard mC1 12AX7/ECC-83 Blackburn tube!