ARC VT100 with KT-120 tubes ?

Karma16..Have a nice day.

I am considering purchasing a VT100MkII. Any preferences on/compairsons between the VT100MkII and the VT100NkIII?

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.

Howdy!
Some slight technical corrections:

Bifwynne, you wrote:
"the KT-120's ability to handle plate current of 700V dc (versus actual bias being set at 65mV dc) is impressive."

700VDC is plate voltage (Volts DC), not current.

Karma16, you wrote:
"Until you prove me wrong, I stand by Ohm's Law and state that simply installing KT120's will not increase an amps power output."

Ohm's law does not apply to tubes, because tubes have plate current/voltage CURVES, not straight lines.
Ohm's law is a first order equation, therefore it represents a linear relationship between voltage, current and resistance. its graphical representation is always a straight line.

Also, a tube with a different set of voltage / current curves may interact differently with the same output transformer at the same bias point, because the OPT does not follow Ohm's law either. An OPT's main electrical spec is impedance, a non-linear measurement, it varies with current AND frequency.

So I guess we are all laymen and should wait for the manufacturer's findings.

In the meanwhile, do not pop KT-120s into your 6550 tube amps, KT-120s draw more heater current and may burn the power transformer beyond repair.
Enjoy the music!

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.