Mullard 12ax7 dating
In a separate cartouche there often is a two character alpha code which denotes manufacture date eg AA.The first letter denotes the year and uses the entire alphabet except for I and O and started in 1945. In a similar fashion the second letter denotes the month of manufacture with A denoting January and M denoting December.A microphonic tube will ring, howl or produce general feedback problems.It will be more noticeable at louder volumes or when used in close proximity to a speaker, typically in combo amps.
When used in this application most tubes will generate some noise if you tap on them with a pencil during operation. Box and orange writing appear to be authentic when compared to 6GK6 in picture above. Date in orange writing is (8136) 36th week of 1981. This tube is marked "made in England" in orange lettering.All tubes were used at the input amplifier stage of the amp since this seems to be where most people develop their perceptions of how good a pre-amp tube is.Back to top The musical detail or ability to reproduce the sound of the instrument is a key factor in assessing a tube for guitar amplifiers. Each one has strengths, weaknesses and certain factors that contribute to its overall ratings. Papesa appears to be a misprint in the Philips data. 12AU7/ECC82 code: Gf8 (NOKEY)9C2 - NOKEY is Heerlen, Netherlands 9 is 1969 date. Mullard tubes and valves of all kinds - we have largest supply of Mullard Tubes in the world! Contact us or drop us line, we have limited quanitities of limited tubes.For each tube used in the test, two were taken since there was no pre-screening involved.The aim was to get a sample that would be practical to work with but allow for variations in the tubes or prevent picking the only dud in a lot. One was a 100-watt Trace Elliot Speed King with 4 x 12 cabinet, and the other was a Fender Blues Junior combo amp.