Identifying RCA-manufactured tubes

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:

RCA-manufactured tubes with 274 factory code

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.

Examples 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.

distinctive markings of the Sylvania 12AX7A

In the example below, this tube is branded as an RCA, but was in fact manufactured by Sylvania. Compare to the Sylvania-labeled tube.

You can see that Sylvania manufacture is obvious.
It just looks like an RCA…