This article provides examples of RCA-manufactured tubes.
RCA is probably the most famous tube manufacturer in US history, and many other companies sold RCA tubes repackaged under their own brand name. The RCA (EIA) code number is “274″ and proves RCA was the true manufacturer. Here are several examples:
In this photo, from left-to-right, are RCA-manufactured tubes with 274 codes — a Magnavox, Emerson, and Motorola. The 4th tube is RCA, and you can see the comparison.
Example of when a tube is branded by RCA, but was NOT manufactured by RCA:
Example: Stacked printed designation “12AX7A ECC83 7025”.
Here is an example of unique Sylvania-manufactured designation for 12AX7A tubes, where the tube is printed as “12AX7A ECC83 7025” vertically stacked. In this example, this tube is branded as an RCA, but was in fact manufactured by Sylvania. Compare to the Sylvania-labeled tube.