Great question John and I don't want to hijack this tread but I would very interested in any ones opinion of the TS KT120's and in which amp (mainly because it is such a new tube and I am also considering them).
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Well I service C/J as well as ARC and it's funny you mention it because I asked them about KT-120's last week. Their answer was..."We do not plan on using that tube". So there you go. Because of the increased heater current when using the KT-120 it's possible they would not be compatible. I'm just speculating as they did not give me a reason.
This does not directly answer your question, but when I owned a Premier 11A the previous owner had been using KT-88s. He thought that they sounded great but wondered why he kept blowing fuses and why the tubes needed frequent biasing and replacing so often. Although it metered OK, the amp sounded so bad I thought that it might be defective. On a whim I ordered a quad of EH 6550s and after replacing the KT-88s the amp sounded wonderful and no more blown fuses.
I used to have a Japanese customer, a very old school and old money guy who was raised very traditionally. When we would go out for sushi he would shudder every time I would add wasabe to my soy. He would admonish me "if the Itamae (sushi chef) wanted you to have more wasabi, he would have added it to the sushi!"
Long story short - I don't think that it pays to try and second guess the designers of the amp.
Basically, I agree with your last sentence. However, I think there are exceptions. For example, I have modified my ARC D250 Mk II Servo amp. It was designed in the mid 1980's. At the time, it might well have been the finest amp you could buy. J. Gordon Holt (RIP), the founder of Stereophile, thought so. I bought mine used in the early 1990's. By the year 2000, one of the things that had changed since the amp was designed was capacitor technology. The D250 had the finest Rel caps available at the time the amp was designed.
Around 2000 I decided to replace all the interstage coupling capacitors with the latest and greatest. MIT was my manufacturer and technology of choice. Unfortunately they did not manufacture caps with the necessary voltage ratings. In fact, no one did with the capacitance value I needed. Were the original Rel caps a custom design for ARC? Could be. They certainly were not in the catalogs.
After a long search I decided to request a custom design from MIT. They agreed and we struck a contract (I had to pre-pay). They were expensive which was mostly a result of the limited production run of 20 pieces. Of course, even their off the shelf standard capacitors were expensive. Mine were more so. After 6 months I had the capacitors.
The new caps definitely improved the sound of the amp. Better resolution, transparency, and speed. This amp was already excellent in these areas. I'm certain that if the amp had been redesigned the caps would have been replaced with more modern improved designs. I simply anticipated the redesign that never happened.
At this time I do not plan on replacing the 6550's with the new KT120's. However, once more is known about the KT120 performance in older amp designs, I might change my mind. The KT120's will not result in more power but might offer significantly longer tube life.
And there have been no downsides to my cap upgrade. The amp just keeps chugging along and I love it. It's truly a great amp.
Sparky, not to sound argumentative; but I do not think that upgrading the caps in an amp is the same as swapping a non-spec'd power tube. Capacitor technology has improved significantly in the last 30 years, and there is little to no risk in replacing old caps with new ones of the same (or compatible) values. But that's not the same as a power tube substitution, which in many cases compromises the integrity of the system design.
I'm not implying that it should never be done, but in my book it's an all bets are off decision. I'm not interested in being an unpaid beta site with my good tube gear.
Br3098 I totally agree with you. Caps can make a huge difference and not all caps work well as coupling caps. There are caps I would use for crossovers that I would never use for coupling caps and vice versa. The bottom line is: all these tweeks, be it caps, or tubes, or speaker wire and interconnect cables are tone controls. Shaping the sound to the room and your taste.
I also want to upgrade my amplifers. I want to upgrade the capacitors, resistors and wiring. CJ announced they have capacitor upgrade C1 for old amplifiers. They ask 2000 Dollars for each amp. I think I will go for Mundorf caps. I used to have Unison Research S8 amp, I modified it with Mundorf caps, Japanese tantalum resistors, good wires and DACT attenuator. All this mods took the amp to another level. But it took about 300 hours for breaking-in, wich drowe me crazy.
I totally agree. A cap upgrade is pretty safe and I believe I indicated that. I just wanted to not discourage folks from certain kinds of upgrades that are safe and can really add to the sonic experience. Tubes are a different story and should be done very carefully.
My guess is I will never upgrade to the KT120. The differences with just the heater current, while not great for a single tube, adds up when you consider that I have 16 6550's not counteng the regulators. The resulting added current may well overload the heater supply. I'm very curious about others experiences.
Karma if you want to upgrade your amp replace all the electrolytic caps in the amp if you haven't already. That will make a huge difference especially if that amp has the old style twist lock lytics on the high voltage side. ARC's upgraded caps have an adapter on them. They are not twist locks but with the adapter plate they provide it's a drop in replacement. Twist locks have high ESR. When I upgrade an ARC amp I always replace them. Also I don't have a circuit diagram in front of me but if you own the MKII servo and your so inclined I would find a better ic for the servo. Put in an IC socket so you can easily remove them. Servos IC's do have a sonic impact. Servos were a good idea at the time, but they're not really used all that much anymore.
Why in the world would I follow your advice? In a previous thread you made claims that I questioned. I asked you to back up your claims by telling us what your test methods were. This is a fair question. You refused to do so. Scientifically, your attitude is simply not acceptable and inspires suspicion.
As far as I'm concerned you are full of hot air and are just trying to impress the naive. But you can't fool me. With me you have zero credibility. I have all the test equipment and knowledge to stand on my own. Your input is not trusted or wanted.
I have been using sed kt88's,and have also tried golden lions in my premier 12's.I noticed very small diferences between those brands.I installed kt120's wow!bass has explosive dynamics,very natural and effortless, a much greater sense power and ease the sound stage is now deeper and wider,midrange is also expanded and more musical the top end is at least on par with kt88's.differences are dramatic I am extremely impressed