KT120 anyone?

[Ears]

New tube, 60W plate dissipation.
Grid No 2 dissipation not so great though, at 8W it's still similar to KT88, so this tube may be aimed at clean high power without overdriving it.

http://audiokarma.org/forums/showthread.php?t=289955

Apologies if it's already been posted , I haven't been in the garage much recently.

[Andy Le Blanc]

EH KT90 is a good product, they work well as a super tweed.
GT used to market a KT100, I don't see any reason why a KT120 would be
any less or more usable. I have seen some comments on the reborn
tung-sol brand that early run products have been dubious, my only worry.

In a general application KT90 are wonderful, you can push the plate dissipation
and the tone is very good. With a higher plate voltage they crank as far as
the watts go and present program nicely.

You could do a twin with two tubes using KT120. A quartet would be nutz
with enough current in the power side.

Is there any published tube data?

[FYL]

New tube, 60W plate dissipation.

Old Russian tube elements, repackaged. Not a new tube, and not a Tung-Sol.

Silly specs such as a max grid leak resistor of 51K (yes, 51K) in fixed bias appplications and a 1.9A heater current. It won't properly work in any fixed bias amp designed for 6550's and derivatives, despite what NS states in their PR blurb: "When used at the parameters found in existing 6550/KT88/KT90 circuits, the Tung-Sol KT120 is impervious to overload, delivering peak power with extreme reliability and long tube life."

Wonder who their PR agency is. Sounds like Hogwash, Bullshit and Associates.

[David Root]

I believe the old 6550 grid leak spec was 50K, but they work fine above 100K.

Whether that translates to a new tube is debatable. That 1.9A heater requirement is a practical problem too.

The published curves look a little flaky to me.

Are these old design, new production guts or old production guts? That could make a difference in reliability.

If it's real it looks like an 8417 on steroids.

[Andy Le Blanc]

Here's the sheet, the genalex KT88 lists it's Ih at 1.6 A ,not too far off.

The upper Ih on the proposed KT120 can be an issue.

The thing with an amp that is designed around a tube type is when you put
the new "super tube" in it, the power side is only gonna produce so many ma..
The new tube ratings exceed what the amp can make, so you get a long life claim.

I've seen published grid return values for fixed bias on other types like that,
they didn't pose any issue in practice for most applications.

If your gonna run the device with 850v on the anode like the sheet says you
can it will be a different story, I'd mind the published limitations.

Any way.... it look like its still cheaper to buy out old Russian mil. stock piles
than it is to hire people in the USA to develop and manufacture tubes.

The EHKT90 is a nice tube despite its origin and adaption, they're probably
gonna try to follow the same formula with this KT120, it'll be fun to try a pair.

I've run 8417.... jeez... they were fun still have pair in the bench spares.

60w @ 450v....thats around a 300ma requirement for a pair, thats a big PT
just with a static bias.

[FYL]

I believe the old 6550 grid leak spec was 50K, but they work fine above 100K.

You're correct. But why repeat the same old mistakes and underspec a supposedly new tube?

That 1.9A heater requirement is a practical problem too.

It's actually specified at 1.7A min and 1.95A max (!) with 1.9A reportedly being the average for design purposes.

The published curves look a little flaky to me.

I don't trust NS datasheets, and this one - Russian translated in pigdin English - is no exception.

Are these old design, new production guts or old production guts?

I'd say new production guts based on old templates. Kinda stretched plates et al.

[David Root]

I would feel better about it if the screen dissipation were higher. How would this tube perform in a typical Fender or Dumble circuit with 450-500V on the screen?

I've run a pair of 8417 at 520V in UL, 100W of clean warmth!

[Andy Le Blanc]

its 8w @600v on g2 Whats the typical ma on a screen grid in a fender?
8w at 500 is around 16 ma., screen grid resistor choice..... a 5881 g2 max is around 3w
it'll do fine.

[jelle]

Just design the amp to these specs. I'd love to try this tube.

[jbefumo]

Any thoughts about the possibility of using the KT-120 to make 20-25W in a single-ended class-A config?

Thanks.

Joe

[JazzGuitarGimp]

This tube has been on my radar screen for nearly two years. NS claims 150 watts from a duet. It certainly looks interesting.

[Cliff Schecht]

I built a quad KT-120 bass amp recently and it was all the way loud. ~550V on the plates and each tube idled about ~75mA IIRC.. They get REALLY hot though, enough to where I'm installing fans in that amp once I get some time. Here's a gutshot before I put in the final e-caps.. I still owe you guys a proper build thread, maybe after the thesis is finished..

[img:960:574]https://sphotos-b.xx.fbcdn.net/hphotos- ... 6730_n.jpg[/img]

[M Fowler]

I think 550 plate volts is too low for these monster tubes so I'm going to find a larger PT.

Mark

[rp]

I built a quad KT-120 bass amp recently and it was all the way loud.. I still owe you guys a proper build thread, maybe after the thesis is finished.. :

You built something this nuts and didn't show it off? You are a most humble man.

[renshen1957]

New tube, 60W plate dissipation.

Old Russian tube elements, repackaged. Not a new tube, and not a Tung-Sol.

Silly specs such as a max grid leak resistor of 51K (yes, 51K) in fixed bias appplications and a 1.9A heater current. It won't properly work in any fixed bias amp designed for 6550's and derivatives, despite what NS states in their PR blurb: "When used at the parameters found in existing 6550/KT88/KT90 circuits, the Tung-Sol KT120 is impervious to overload, delivering peak power with extreme reliability and long tube life."

Wonder who their PR agency is. Sounds like Hogwash, Bullshit and Associates.

How about : "Dewey, Cheatem, and Howe"