Thanks Hifigeek1: I spoke with a tech guy at ARC yesterday about the KT120. He confirmed what you are reporting above, although he did not know for sure who the manufacturer is. I did some on-line checking and noticed that the only label for KT120 tubes is Tung Sol.
As far as compatibility is concerned, the ARC guy said that the VS 115 could physically and "should" (that's my quote, see below) technically handle the new tube. Because the VS 115 has an open topology, its ability to physical accomodate the KT120 is a no-brainer. Most significantly, as to the all important question of sound quality, he advised that ARC believes the new tube should make the ARC VS115 sound better. There's also the added plus of a slight boost of output power.
On the other hand, when I pressed on the "technical" issue re electronic compatibility and power transformer over-heating, I sensed just a smidge of tentativeness because he did not have tech sheets in front of him. FWIW, out of an abundance of caution, I will wait until I see something in writing from ARC about the tube change. As a fellow A-goner mentenioned in a post, I do not want to chance turning my power transformer into an expensive ship anchor.
The ARC tech guy also mentioned that as long as the "Set" tubes are adjusted as prescribed (65mV), the "Check" tubes could vary as long as they were within the 57-73mV spec. Out of an abundance of caution, Hifigeek1, I tend to agree with you about tapping down the "Set" pots to bring the "CHeck" tube bias current down.
Happy New Year!! BIF
As far as compatibility is concerned, the ARC guy said that the VS 115 could physically and "should" (that's my quote, see below) technically handle the new tube. Because the VS 115 has an open topology, its ability to physical accomodate the KT120 is a no-brainer. Most significantly, as to the all important question of sound quality, he advised that ARC believes the new tube should make the ARC VS115 sound better. There's also the added plus of a slight boost of output power.
On the other hand, when I pressed on the "technical" issue re electronic compatibility and power transformer over-heating, I sensed just a smidge of tentativeness because he did not have tech sheets in front of him. FWIW, out of an abundance of caution, I will wait until I see something in writing from ARC about the tube change. As a fellow A-goner mentenioned in a post, I do not want to chance turning my power transformer into an expensive ship anchor.
The ARC tech guy also mentioned that as long as the "Set" tubes are adjusted as prescribed (65mV), the "Check" tubes could vary as long as they were within the 57-73mV spec. Out of an abundance of caution, Hifigeek1, I tend to agree with you about tapping down the "Set" pots to bring the "CHeck" tube bias current down.
Happy New Year!! BIF