THE GREAT MULLARD MAGIC BLOG — stamping code

I am not going to get into the perennial discussion of the sonic properties of the yellow print valves over the stock boring white print ones but instead discuss A DIFFERENT advantage the yellow has over the prosaic white. Some of our eagle eyed readers will have noticed that the Yellow Print Old Shield Mullard valves have underneath the shield typically the valve notation in Mullard - Philips (ECC83) or even RETMA (12AX7) then underneath this is the elliptical BVA logo - just like for the white print valves....... But here's the rub - they yellow valves have a letter code...