This is a closely matched quad of NOS IEC 6BQ5 EL84 tubes, manufactured in Great Britain (Blackburn) by Mullard. The tubes have the typical seams on the top of the glass, Great Britain printed in white at the top, and the B code indicating the Blackburn factory.

These tubes are burned in at the factory, so even new ones have small smokey looking spots near openings in the plate. Just a few hours of use will make Mullard tubes get large smokey looking patches inside the glass. This in no way affects the life or sound of the tube. Mullard typically burned in tubes at the factory.

Three of the tubes' codes at the base are identical: B7D1, one tube is B7C1.

Test results:

1) 11,500 @ 49mA

2) 11,500 @ 48.5mA

1) 11,500 @ 47.5mA

1) 11,500 @ 49mA

These tubes are a rare find! Contact us if you have any questions whatsoever.