This is a letter I recently wrote to Bob Pletka, president of Eurotubes.
I notice that there are not a lot of customer comments regarding the usage of JJ Tubes in a Hi-Fi application. Well here's my take on using the JJ 12AT7 and E34L's in my VTL 225 monoblocks powering Hales Signature 2 speakers.
Originally the amps were tubed on the output with GE Fat Boy 6CA7/EL34's (8 per amp). When I consulted with you I learned that the GE version was not a true EL34 tube, but rather a kluged up version of a 6L6 adapted for EL34/6CA7 usage. The original 12AT7 was by EI (actually not a bad tube in this application). At any rate I took the plunge and replaced them all with JJ's.
The amps have truly been transformed. Throughout the entire frequency spectrum the sound has been tightened up. The increase in detail was very evident. The midrange is a bit more forward but not in a "Brightness" sense. It is just more clear and detailed. With the new E34L's in place, it became evident that the punchy bass exhibited by the GE's was a bit bloated with too much bloom. The bass with the JJ's is much tighter and natural sounding. The treble was more extended and much less hashy. The harmonics and overtones are wonderfully articulated, again very natural with little artificial bloom.. There is a great sense of width and depth within the stereo image. It took me about a month to get used to this "new" sound. I noticed it took a little longer warmup time until the amps became dialed in but the extra wait was well worth it. The VTL has actually gotten closer to a transistor sound due to it's increased detail retrieval capabilities. Both tube types are extremely balanced throughout the entire frequency range. I must say I am impressed with the quality (and the price!).
I would like to tube roll the JJ 12AT7 with the long life Telefunken version but they are very expensive and tough to find. I am sorely tempted to cryo treat the JJ 12AT7 and if I do I will report back.
Thanks for your advice. You were extremely helpful.
These tubes are worthy of your consideration when considering replacement and Bob is quite qualified (and willing) to discuss your tube needs.