More on the Philips & Siemens: They were produced in the same year and month. Although the xf1, xf2, xf3, xf4 is usually associated with Mullards. These xf codes were used by Philips, Mullards, Siemens, Valvo, Brimar. Mullards usually have an xf code a 'B' code representing Blackburn plant. What's also interesting that xf4 code on my Philips/Siemens is much older than the xf4 codes that appears on Mullards. Philips xf4=~1957-1962 whereas Mullards xf4=~1976-1980 My tubes with code xf4 L0L were produced in the same factory, year and month: xf4 = EL34 tube L= Sittard/Holland 0= 1960 L= December
Thank you for the exceptionally thorough research and the wealth of knowledge you've shared regarding identifying and distinguishing vintage Telefunkin NOS EL34s. Your detailed analysis and insightful tips have been incredibly helpful for audio enthusiasts like myself who cherish the rich sound and history of these classic once in a lifetime components. Your dedication to preserving and sharing this knowledge is a true service to the audiofile community and generations to come. Great Reference video! 👍🏼
