"The earlier a signal is in the audio chain, the more important it's amplification is." This truism places the 12AX7/ECC83 class at the top of a list for the most important tubes in your amplifier. If you have done any tube rolling, you know from experience that the 12AX7 has more effect on amplifier sound than the following 12AU7 or any other low/medium gain stage. The reason has to do with the high gain characteristic of the 12AX7 (or other high gain tubes like 12AT7, 12AZ7, 12AY7, etc.) High gain is used successfully only on very small signals--hence high gain tubes are the first in line for phonograph or microphones or tape heads. If you have never used a high quality vintage old stock 12AX7/ECC83, you will be stunned at the difference. We are documenting our listening tests to help you select the proper vintage tube.
A little bit should be said about the equipment used. The soon-to-be-released custom phono/line stage amplifier from Old Stock Audio has phenomenal articulation and uniquely reveals the subtleties of the tubes. One of the features of that amplifier is that many of the audio path internal components are also old stock and hand selected including OIP (oil-in-paper) capacitors, military quality hardened switches, and hand built transformers. This pre-amp feeds an E80L amplifier driving a pair of Teresonic Lowther-based speakers. This setup truly reveals even the minutest details.
The oldest USA tubes are black plates and all of them are superb, but some really sing. We tested after separating both by manufacturer, and construction/date.
RCA LONG RIBBED BLACK PLATE:
1. Long 'D' Getter, early 50s, White Lettering: The tone was excellent and even with very good articulation. The timpani attacks in a large symphony recording came through sharp and musical. The ambience was engaging. One listener commented "There is so much room in the sound". Highly Recommended
2. Large Horseshoe Getter with double crossbar mount, '50's, ULTRA-RARE!: If you took the tubes from #1 and sprinkled magic fairy dust on them, you might come close to the sound of this tube. Far superior IMHO to a smooth plate Telefunken--I did NOT want to stop listening. Utterly Sublime, and very rare.
3. 7025 Bent 'D" getter, Orange Lettering and reinforced top mica: The 7025 label is often a military version, or ruggedized version of the standard 12AX7 or ECC83. This tube was very similar to #1, but we felt that solo instruments came forward in the sound stage just a little more. A classical guitar solo entranced us, as did the french horn. Highly recommended.
4. JRC (Military) Long 'D' Getter, White Lettering, early '50s: Again this military version of #1 was very similar to it, but with even greater resolution of the sound stage and articulate subtlety. The bass was tight and wonderful. Descriptive words: Subtle, Gentle, Strong, Fast. Very Highly Recommended.
5. Early '60's Long D Getter, Orange Lettering: Not as articulate as #4 or #2, but still very musical and smooth. Reminded me more of a Sylvania style sound than traditional RCA. Recommended.
6. U-Getter with Foil Crossbar, White Lettering, early '50's, ULTRA-RARE: Absolutely wonderful sound! Enormous sound stage. Super articulation without any harshness. Tight Bass. Possibly my favorite Black Plate.
RAYTHEON SHINEY LONG BLACK RIBBED PLATE:
There are seven different styles of 1950's and early 1960's Raytheon 12AX7 & 7025 that we were able to categorize. The sound was so similar in all varieties that it is not possible to break them out individually. As a class of tubes, the black plate Raytheon are truly superb--equal to the best of the RCA. The Raytheon sound has a hint of darkness added to the detail. In passages like the middle of the first movement of the Dvorak 9th, this darkness exposes the melancholy of that passage and makes the listening experience almost transcendent. I love the Raytheon black plates and highly recommend them without reservation.
Sylvania Black Plate:
Sylvania is traditionally known for its smooth and musical sound. It is close to Mullard in that sense. The Sylvania vintage black plate adds articulation that is near to TungSol along with a large sound stage and very tight bass. Another feature that is common to the Sylvania line is their ability to handle complexity. Reproduction is faultless, and in the case of the Sylvania Gold Brand, absolutely unmatched. The Sylvania Gold Brand/Gold Pin are not black plate, but they are my all time favorite 12AX7. These are factory graded for low noise and have a very long break in period. I only wish they were not so rare. I highly recommend all Sylvania Black Plate and Gold Brand tubes.
TungSol Black Plate:
I almost decided not to include the TungSol Black plate because they are so rare and generally unavailable, but there is an excitement to TungSol Black Plate that is unique. Whereas the Sylvania Gold Brand are unmatched in their neutrality, the TungSol black plate are unmatched in their articulation and attacks, without losing the tonal beauty. It is a matter of personal choice and amplifier type as to which 12AX7 is right for your system. My system is one that reveals details so I tend to use the Sylvania Gold Brand for symphonies, the Raytheon Black Plate for solo and ensemble, and the TungSol Black plate for Jazz and Rock. Highly Recommended.
GE Black Plate:
Finally we come to the GE Black plate in the USA line-up. Most of these are labeled Kenrad, but they were made by GE. GE gets a bad rap a lot of the time, but it is not deserved. Their quality control was excellent and tube to tube similarity is much better in the GE and Raytheon lines than in the RCA lines. The GE Black plate 12AX7 (and 5751) have an enchanting and beautiful sound. Articulation is excellent, though not as detailed as the TungSol. Sound stage is expansive and inclusive. As an all around tube you cannot go wrong with the GE Black Plates. They are great performers and very durable. Microphonics is rare in the GE line—again due to the excellent quality control. I use GE tubes as my everyday and background listening tubes. Highly Recommended.