Anybody tried KT120 tubes on Conrad Johnson amps?

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.

HI Br3098,
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

Chris at Parts ConneXion recommended the new KT120's for my Power 2. I love the tubes and wrote a thread awhile back.
Chris seems to be very knowledgable about things audio as well as KT120's.kkurtis

HI Kkurtus,
What is a Power 2? How much did you pay for the KT120's and how many of them are in your amp? It's my understanding that they are significantly more expensive than good 6550's. Where did you buy them?

Are they better that your 6550's? In what way?

Sorry, lots of questions.

Sparky

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.