It is a P.I.T.A. to open the preamp, but while you're at it, you may find it interesting to try to decipher all of the codes. So here's how to read the rest of the codes. In the second row, there are usually 4 characters, which signify as follows, in this order: [factory code][year of production][month][week]. So, "*3A4" would mean made at Amperex Hicksville factory, in the 4th week of January 1963 -- a nice vintage!
The codes on the first line stand for [tube type] and [??]. "VR" means a 6DJ8 type (i.e., a 6DJ8, ECC88, 6922, E88CC, 7308, or E188CC). The significance of the last number is murkier - it seems so signify the number of the batch or production run. Whatever it means, the lower the number, the older the tube. So VR4 is older than VR6.
Tubes made at the Hicksville factory were just about always branded Amperex and tubes from Blackburn were almost always branded Mullard. But the Heerlen factory pumped out a lot of (excellent) tubes and they could have been branded Philips, Amperex, Mullard, or Valvo. The Valvos usually sell for a little less; I'm not sure why, but the Valvo name is less prestigious and some assume that a Valvo was made at Valvo's German factory (not as good, imho). But if the factory code indicates Heerlen, well, a Heerlen tube is a Heerlen tube. The brand name means nothing. They're excellent.
The good news is that, even if your tubes were made at the same factory, they're all good, just different flavors, and you would have two nice sets of tubes. 'Can't have too many toobs. (But take that with a grain of salt -- your writer has a drawer full of these -- which is what led me to research and get to know the coding.) Happy decoding, James
