Hi Davey.
No conclusions as stated, just one man’s opinion for a given system. Actually, Acoustats with two panels or more per side are a relatively easy load for most (tube) amplifiers, the impedance does not drop very low until the high treble. And my Acoustat interfaces have been rebuilt and the bias increased to make them an even easier load for my amp
I’m not saying the Teles are a bad tube (for one thing they are incredibly well made—I have collected 20 samples and they all test strong and well matched), but in the Rogue I find them thin sounding and lacking in “bloom”in the midrange with bass that does not compare to American black plate tubes from the same era. The Tung Sol KT120 are not a good sounding tube in my opinion and many people share that opinion. Sure they are powerful and punchy, but also harmonically lean and dry in the midrange. As “solid state” sounding an output tube as you could possibly find. I understand that some people would like that sound, but it’s not for me.
Have you tried a Raytheon or RCA black plate 12ax7 in your amp? Or a triple mica black plate 5751 from Sylvania or GE or RCA? A very different type of sound from the Teles. I find the Mullard short plate 12ax7s from the 1960s to be almost the opposite of the Teles, they go to far with bloom and richness in the midrange until the music sound a little thick and bloated. Again, in some systems and to some listeners this works. There is no right or wrong in tube rolling.
I can and do alter the sound of my amp and system with the tubes I use. To me this is one of the things that makes owning tube equipment fun. I still have an old Adcom amp here, and a Quad 606 that I used for many years before I got the Rogue. I think the 606 is a good amp, modern Quad amps still use basically the same circuit. But when I switch it in to drive the Acoustats I lose interest in the music. I just don’t want to sit and listen to it, it doesn’t involve me. It sounds like an electronic reproduction, not like music. Granted, I have not tried a big $$$ solid state amp in my system. And my Rogue has been modified with with a lot of expensive parts (and the best tubes of course!). Would love to hear a Pass Labs amp in my system one day.
Obviously my opinion of the TS KT120 is not shared by Rogue Audio. All their amps come standard with this tube. Pity. But many manufacturers like ARC and Conrad Johnson have moved to the KT150 tube (which I have not heard). I think it is just a matter of time till other manufacturers move away from the TS KT120.
