MULLARD CV4003/M8136/12AU7/ECC82 MATCHING PAIR OF NEW OLD STOCK IN BOX VINTAGE VALVES. BRITISH MULLARD MILITARY UNUSED VINTAGE VALVES WITH A WONDERFUL CLEAR WARM SOUND. MADE IN THE MULLARD MITCHAM MILITARY FACTORY IN GREAT BRITAIN IN THE 1960'S.MULLARD MITCHAM "R " FACTORY CODES ETCHED INTO THE GLASS OF THE BOTH OF THE VALVES. THE SAME MATCHING FACTORY DATE CODES ETCHED INTO THE GLASS OF THE VALVES. MADE IN GREAT BRITAIN IN THE1960'S. CLEAN SHINY UNUSED METAL PINS. MULLARD MITCHAM DATE CODES ETCHED INTO THE GLASS OF THE BOTH OF THE VALVES = 6 3 1 R 7 B 4.
MULLARD CV4003 PLAIN MILITARY BOXS WITH VINTAGE BROWN CARDBOARD AND TISSUE WRAPPING. THESE TUBES TESTED AT 100% STRONG NOS READINGS ON MY B&K 747 + HICKOK TV-7 TUBE TESTERS.TESTED FOR GAS AND SHORTS. Philips Holland bought and owned Mullard UK and a many other valve companies in the 1920 - 1960 period. They then branded British made Mullard tubes with their own Philips logo. The British Mullard engineers etched factory codes into the glass of their British made valves, so they knew the difference. Mazda, Amperex, Bugle Boy, Mullard, Miniwatt Dario, and Radiotechnique were all names owned by Philips Holland in the 1950/1960s. The respective names typically referred to factories. For instance, Mullard operated in England. All of these factories may at one time or another produced tubes with various other names attached. Which is why we see Amperex and Mullard tubes made in Holland or Philips branded tubes made in England.
Factory codes etched onto the glass or underneath the base of the tube help us to figure this one out.