ARC VT100 with KT-120 tubes ?

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.

Bifwynne, I will be getting in a VS-115 with KT-120's for service. I will let you know what the power output is once the unit has been gone through.

I talked to ARC today 3/9/11, sorry I forgot the name, but ARC is now strongly recomending that even current products like my Ref 210s be sent back for some power supply adjustments before going with the K120 tubes. He said they have learned more about the K120.

BTW I did not go into any detail since I was calling about another 6550 tube issue and I have 650 hours on my set so I will not be making the jump soon. My issue is a 6550 driver tube that will not hold bias.

I am looking forward to the K120 for hopefully both sonic improvements and reliability improvements over the SED 6550 - but its not like they dont sound good IMO.
Terry

Both the Ref210 and Ref610 require changes to one of the regulated power supplies in those two amps. I will probably be able to update the Ref210 at my office, the Ref610 on the other hand requires a more extensive update and therefore Ref610's will need to go back to the factory.