After this last weekend, the tube configuration on my AMR CD77 is Philips 5687 in the rear, Mullard CV4024 (12AT7) in the middle, and RFT EZ80 in the front. I have heard good things about the Bendix 5687, but havent had a chance to audition them. This past weekend I had some extra time compared four different sets of EZ80s (front position).
Tesla rolled off highs & lows; very warm; sounded like a screen was placed in front of the speakers. I was not impressed at all.
Brimar similar to the Tesla, but not quite as warm and not as rolled off at either end. The mid-range is where these tubes excel.
Tungsram great extension both top & bottom, but poor density. Music had a hallow sound, like listening through a pipe. Also has a bit of boost in the upper mid-range. I had used these previously, but was never happy with them.
RFT- Magic time! This is by far the best tube I have tried in this position. Voices are real; in the room with you real! Thunderous bass, excellent midrange and a delicate high end. If one can find fault with them, it would also be a bit of push in the upper midrange, but far less than the Tungsram. Mind you, Im knit-picking (but isnt that what we all do with this hobby?). I plan on adding a third set of damping rings to the tubes my guess is that it will help control it a bit.
Remember, no tube is perfect. All have their strengths and weaknesses. What works in my system my not work in yours. You really have to experiment to find out whats best for you. In my opinion, this is one of the great strengths of the AMR; you can customize it to your liking. Also, you can easily move the damping rings to different points on the tubes to make even finer adjustments to the sound. Additionally, if your machine is not a 77.1 (the current version), you can have Darren Censullo of Avatar Acoustics modify it to the new standard a substantial improvement!
