I have been collecting tubes for many years currently have around 500 el34 tubes the main production countries were netehrlands and Blackburn, some were labbled as Brimar, mullard, phillips and Valvo.
As far as Mullards go I like the ones from around 1957 to 1962 they have a double ring getter the base wise much wider than the glass itself the bases them self can vary. I found the ones without the guiding pin sound best they have a sense of ease and openess in the midrange which is very nice.
The more common tube is the brown base Mullard where the base is the same size of glass. I have seen the exact tube with the Valvo and brimar logo they sound the same to my ears this tube says made in black burn production was up to 1968. The sound is way more congested and thicker than the earlier tube. It is still very musical.
The 1954 with the code 5x kek flat ring el 34 with the large metal base and flat getter is a great tube I have seen the same tube as a Valvo and brimar its a very powerful sounding tube amazing base needs a adaptor to work.
Dont get me started on 300b and 211 tubes now they can really drive me potty.
I have learnt without trying them in ones system its very difficult so sadly costly mistakes become the norm when trying to find perfection.
There are many many variants I could write about some have different logos etc. I like the Phillips tube with the code xf3 lx lxx with its bakerlite base now this is one beast of a el34 its so so fleshed out in the midrange comes out and simply hugs you. The bass is deep and controlled the top is sweet and liquid. This tube was made in Sittard Netherlands I have not seen this as a mullard or brimar etc. The more common Phillips tube is the one with xf4/5 again stunning.
There were some rare german production el34 tubes that had a flat ring getter I have some not even sure who labbled them they say made in germany I have a code of SYA DX. I think those are great very robust not soft and rounded very controlled.
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