Achim van Duren sent a set of photographs of his EM34 collection. The valve is essentially the same electrically throughout its manufacturing life but external changes are evident. Additionally the EM34 was made by more than one facility.
The first picture shows an EM34 straight out of the box. It is probably of late manufacture and although it has the Mullard name, the gold metalising clearly shows in the lettering that this valve was not made in the UK. The plain box indicates a supply to industry or government (note the CV394). Retail sales would dictate a box with coloured print.
The EM34 above is again in a utility box. It carries the Mullard logo but was made in Austria.
Philips, the owners of the Mullard brand since the late 1920s, produced EM34s for non UK sales under the Miniwatt label. The two examples above show the target market as consumers by the use of coloured packaging. Philips devices proudly carry the made in Holland logo.
The German Siemans example of the EM34 looks very much like the Mullard valve at the top of the article. One may speculate that the foreign maker from the top photograph may well be Siemens.
The much respected Hungarian manufacturer Tungsram are also among the many makers of the EM34. In this example the coating on the valve is red paint.
This Mullard clear EM34 was not made in the UK but is still displaying the BVA logo. As the British Valve Association was a manufacturers club the pressure would have been on all the members to source their products from within the UK.
The final two images are of the EM34 in its government service livery, the CV394. The Siemens offering on the left has a clear envelope, whilst the valve on the right has the familiar red paint. One can only presume that the equipment had its own shielding or the application was less prone to interference.