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In Reply to: RE: Heerlen Philips Factory 12ax7 Date Codes posted by vmazzone@fastmail.fm on December 27, 2014 at 13:03:22
I have included some reference photos taken from past eBay listings to clarify the differences between Copenhagen and Heerlen production for 12AX7/ECC83 tubes.
The first and second photos above show the triangle symbol inverse to your tube (photo 3) - almost a mirror image that represents Copenhagen production rather than Heerlen production.
As you have correctly stated in your eBay listing your RCA 12AX7 tube was made in Heerlen Holland (photo 3) in October 1953. The RCA 12AX7 tube shown in photo 1 above was made in Copenhagen Denmark in September 1953 and the RCA 12AX7 tube shown in photo 2 above was also made in Copenhagen Denmark in January 1951. I don't think the January 1951 date code is correct. I am more inclined to think the tube in photo 2 was made very early in January of 1954 but was tagged with the year of manufacture as 1953. Being a Copenhagen produced tube it could have also been made back in January of 1951.
I hope the above information helps.
Follow Ups:
The triangles can be confusing, especially with old code non acid etched print. Sometimes other clues help identify origin. I don't believe welded long plates were made in the Heerlen factory for ecc82 and ecc83. Other clues such as plate construction suggests Copenhagen origin. However their were welded plate ecc81 Heerlen tubes made in the early fifties with old codes which are often mistaken for Copenhagen. It seems the reverse practice for welded vs crimped plates were in practice for ecc81 tubes. Early fifties Copenhagen ecc81 were however crimped plates ! Go figure.
The ultimate test is to audition the tube for factory sound. A reference tube would be helpful. A Copenhagen should have better resolution especially in the mid range. A Heerlen has more extended treble but overall less resolving. The old code Heerlen also has a liquid more euphonic sound to the Copenhagen making it very appealing especially with female vocals, but ultimately less transparent to the Copenhagen.
Very Helpful XLR!
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