THE GREAT MULLARD MAGIC BLOG — valve etched codes

There is much conflicting fokelore on the internet about the Mullard etched valve codes so I thought I would add our two penny-worth. The etched codes have value to us today as they contain two discrete nuggets of information; firstly, should a valve loose it's printing you can identify the valve type and secondly, you can glean the production site and the month and year of manufacture. The etched codes, in general, comprise of two lines stacked vertically with the top line being a three character Engineering Code with the third digit signifying the development iteration of the valve.  For example,...