ARC VT100 with KT-120 tubes ?

It is possible that the KT-120's are running cooler because the plate of the tube is much larger. Therefore, there is a greater area for heat dissipation and less chance of a hot spot. There are also heat sinks on the plate structure as well, making cooling more efficient. The KT-120 represents the latest state of the art in power tube design.

I bought 6922 input tubes and 6550C output tubes on the internet, but they did not meet the standard and it was impossible for my tech to get the settings right and the bias up to the correct value. He recommended that I got the “authorized” tubes from ARC and I ordered a complete set of new tubes and got the KT120 instead of the 6550C from ARC (or actually from Audionord.se, the Nordic distributer).

This time the tech had no problem getting the setting right and the bias correct and I got the VT100mkII back in no time.

The change in sound was dramatic. Before the sound was easy, soft and pleasant, the amplifier seemed to work fine and I was happy. But now it is much more open, revealing and tight. I listen mainly to acoustic jazz and the double bass is much better defined, the sound from the plucking, the string and body is more coherent as from one instrument (as it is in reality). Drums and especially cymbals sound natural and again the attack and ringing of the cymbal is coherent. The recording of the piano is clearly revealed, but still sound neutral and musical, not analytic.

I find that one of the greatest strengths of ARC gear, is the “recreation” of the human voice. And the voice of Ella Fitzgerald or Diana Krall shines through the VT100mkII with the new KT120 output tube.

Before I could read a book or work on my laptop while listening to music, but now it is difficult to concentrate and, as I am writing this, I have to stop and listen all the time, even to music I have heard a hundred times.

I can second what gmorris writes and I can recommend use of the KT120 in the VT100. And I will absolutely recommend buying the “authorized” tubes from ARC, it can save you and/or your tech a lot of time and trouble.

Farobari I try and tell my ARC customers that all the time. ARC tubes are more expensive but well worth it, especially if you want to get your amp up and running quickly. I also recommend factory trained technicians do this because you are dealing with high voltages in the amp and one wrong move and the results are not pretty. With ARC tubes, I don't have to sit there and let the tube bias settle in for a week. The bias is usually stable after an hour since they had been burned in for 48 hrs. I can run it for an a day, set the bias, do a frequency response and a power output test and return it back to the customer in short order. I had to recently re-tube a C/J amp and purchased tubes from a reliable vendor. Two minutes after I installed the tubes, wouldn't you know one of the EL-34 started running away. And these were supposedly tested tubes that I paid extra for. The point is you really can't trust many tube vendors out there. Granted, it's possible the tube got damaged in shipment. I find that with ARC products, installing non-ARC tubes in their products is like putting low octane gas in a Ferrari.