gibosi
Headphoneus Supremus
- Joined
- Oct 18, 2012
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AJ1 suggests that they have the same construction. They conform to the first revision. That is, when the tube was first introduced, it was AJ0. The first revision is AJ1. To my ears, all AJ1 sound the same. And so there is no difference in sound between 60s and 70s production.
Here is the key to Philips production codes:
https://frank.pocnet.net/other/Philips/PhilipsCodeListAB.pdf.
R7K1 is likely the first week of November, 1967. R8H4 is likely the fourth week of August, 1968. And the third tube can be dated according to the CV code:. Z = 1968 and J = September.
https://www.tubecollector.org/cv-valves.htm
Here is the key to Philips production codes:
https://frank.pocnet.net/other/Philips/PhilipsCodeListAB.pdf.
R7K1 is likely the first week of November, 1967. R8H4 is likely the fourth week of August, 1968. And the third tube can be dated according to the CV code:. Z = 1968 and J = September.
https://www.tubecollector.org/cv-valves.htm