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I've got a nice selection of NOS 12ax7 tubes, however some of the print on some of the tubes has faded or rubbed off quite badly. The tubes sound great, however I'm having a little difficulty in positively identifying them. I'm hoping that some of you here might be able to help:

1. Short ribbed grey plates (almost identical to those on the Bel 12ax7 and a Mullard that I have). The only print on the tube is a small rectangular marking (with squared off corners) - inside the rectangle it says "12AX7A" and above the rectangle it says "USA".
2. Short box grey plates. On one side of the tube, there is faded thick grey print down the length of the tube - "12", "AX7", "A", "USA" (each set of characters indicated are under the preceding character). On the other side, the print has smudged but is a fairly bright red/orange color - there are two rows of print .. I "think" there is an "RCA" on the top row and "12AX7A ECC83" on the second row (I'm fairly sure about this being an RCA tube, but just want some confirmation).
3. Short box grey plates (similar, but not exactly the same as the previous tube). On one side of the tube, near tip, thin grey print - "12AX7". On the other side, lime green print (two rows) - second row says "Made in USA". First row is hard to make out .. but I think one of the characters is a "G" and there is "12AX7" following this (can't make out if an "A" follows the "12AX7" or not).

Both tubes 2&3 exhibit similar sound characteristics - warm clear tone; good bottom & top end, medium gain.
Tube 1 is warm, nicely balanced, more gainy sounding (in fact, similar to the Bel 12ax7).

Hoping someone out there might have some ideas??

REGARDS


Barry M

Many (if not all) of the RCAs I have seen have that box with angled corners and the tube identifier inside. Some have USA above it and some don't. Any time you see that etched into the glass, there is a very good chance it is an RCA.

Orange lettering is also a good indicator of an RCA. I can't think of any other tube with orange letters. The RCAs with orange lettering do have two rows as you describe.

If yours look like the one in the picture (from V1 in my Lightning no less), you have a winner!

I'm not sure about the one with green letters. It could be a rebranded RCA or GE or something.

S2 .. now we have a dilemma .. lol .. although I guess RCA manufactured quite a few different types of 12ax7 tubes over the years ..

There is a definite similarity between my "tube 2" and your first pic - the orange etching looks pretty much the same (can't be 100% sure, because of the smudging) and the box plates look identical (as far as I can see from the pic). However, the interesting thing is that my "tube 2" matches your second pic .. except for the plate structure. Perhaps I have two different RCA tubes here (which is what I originally guessed) - they sound very different though .. which isn't that unusual I suppose given the different plate structures of each.
My guess on tube 3 (green etching) was that it might be a GE or Ge military version.

Thanks

Barry M