ARC VT100 with KT-120 tubes ?

Karma16: please back off Hifigeek. We should all be respectful to each other. Moreover, he has always provided good advice to those of us who are less informed about electronic theory, particularly ARC gear. Oh, my rig is all ARC: PH-7, Ref-3, VS-115 and CD-7. I can personally attest to the very helpfulp advice and information that Hifigeek has always provided.

BTW, the ARCDB website has some info on increased power output for various ARC amps that use the KT-120. See the News tab. I don't know, or frankly care for that matter, where ARCDB got their information.

If you do a broad "KT-120" search on the A'gon discussion forums, I think a number of ARC owners have posted comments about the superior sonic attributes of the KT-120 over the 6550. Is it true, I guess you'll have to spring for the new tube and try it yourself.

Will tube life be extended? We'll just have to wait and see. However, Hifigeek's comment about the KT-120's ability to handle plate current of 700V dc (versus actual bias being set at 65mV dc) is impressive. As a lay person, it would seem (?) that the new tube has a robust build quality that may possibly extend tube life over the 2000 maximum hours suggested for the 6550.

Thanks to everyone for their helpful advice.

Thank you Casouza for your helpful explanations. Just to be clear, I appreciate your clarification that current and voltage are different concepts.

However, I quote from Hifigeek above that "(t)he tube is capable of running up to a maximum plate (VOLTAGE) at least 700Vdc. The hope is that tube life will be extended." Casouza, I should have said that "the KT-120's ability to handle plate (VOLTAGE) of 700V dc (versus actual bias being set at 65mV dc) is impressive." Quite honestly, not being an electronics techie, I have no idea whether VOLTAGE handling capability will or will not extend tube life. Hopefully, it will.

Finally, I think your advice that one should not replace 6550 tubes with KT-120s because of concerns about increased CURRENT draw on power transformers is correct. FWIW, I spoke to an ARC tech rep about the issue. I was told that the newer models can handle the KT-120 without the need for a mod. FWIW, the ARCDB web site states that the output tubes on the VS115 amp were changed over to the KT120 tube in Nov 2010. By contrast, I didn't see the same notation for the VS115 on the ARC web site. I don't know where ARCDB obtained that info, although I believe it to be correct. In short, I too would advise anyone thinking about changing out 6550s for KT120s to call ARC or their respective amp mfg'er before changing out the tubes.

Thanks again Casouza for the explanations.

Thanks Tdaudio for the power supply info. That's good to know.

Hifigeek, do you know anything about the power supply adjustments that Tdaudio mentioned in the post above? Also, just curious about the VS115 you have for repair. What's the problem? I'm interested because I own a VS115.

Tdaudio and Hifigeek: spoke with Chris at ARC today. Was told that REF210 and REF610 will require mods, as mentioned by Hifigeek above. However, the VS115 and many others are ok as is. Until something comes out in writing, I would still call to double check for yourselves.

Chris also said that ARC is not in a position to say that the KT120 will have extended life over the 6550C because there is not enough history behind the new tube and a lot of variables are in play that can affect tube life. However, ARC does believe that the new KT120 sounds better than the 6550C.

In my case, as I get closer to the 2000 hour mark for my current set of 6550C tubes, I will probably consider dropping in the KT120s. I'm very curious to hear how they sound. FWIW.

Thansk Hifigeei and Casouza for the tech information. Hifigeek, care to share what's wrong with the VS115 you're working on??