ARC VT100 with KT-120 tubes ?

HI hifigeek,
Well, you never addressed my questions. I don't know what to think. So, are we to assume that your tests were in some way flawed? That the KT120 was not resulting in more power but you won't admit it?

Since you made the claim of increased power but then won't back it up by defining your test methods, we should be very suspicious. Your good name alone won't validate the tests resultes for me.

If it were me, I would have tested the original 6550's to determine their freshness, run power tests with the 6550's using ARC's THD spec as the control, then, test the amp with the KT120's using the same ARC THD. If you wanted to be really precise the AC line voltage should be monitored. This is the only way to determine relative power outputs.

I think you know all these things. But knowing and doing are two different things. The folks who read this thread may not understand how power tests are run and, thus, have no way to evaluate your results.

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.

Sparky

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!