[Ericus Rex]

Anyone directly compared the Tung Sol KT120 with any of the primo versions of the KT88 like the Canada Fuller, Psvane, EAT or even the Black Treasure?  I've heard great things about the KT120 but no talk of how it compares with the best KT88s.  Thx!

[roscoeiii]

A very good question...

[richidoo]

It draws more power, many amps designed for KT88 won't be able to handle KT120, so you gotta choose an amplifier that can handle both before doing comparo.

I am impressed that ARC has chosen KT120 as their new standard power pentode. No more 6550C for new designs.

[roscoeiii]

It draws more power, many amps designed for KT88 won't be able to handle KT120, so you gotta choose an amplifier that can handle both before doing comparo.

Yes Richidoo, a very important point!

And it should also be noted that in many amps the KT120 will not result in increased power. See for example the Stereophile measurements of the Rogue Titan Atlas Magnum:

http://www.stereophile.com/content/rogue-audio-titan-atlas-magnum-power-amplifier-measurements

[rpf]

I compared the KT120s to the Genalex KT88 re-issue and Penta KT88SC in my Rogue Cronus Magnum.

It wasn't even close. The KT120s had bass that was just as strong, with a more balanced mid-range and treble. Dynamics and soundstaging were also greater with the 120s. Although all the tubes put out the same 90wpc that the Cronus circuit is limited to, the 120s sound far more powerful.

I have not heard the specific KT88s you listed but the Pentas are also made by Shuguang and are supposed to be very close to the Black Treasures. (Fwiw, I did compare the Black Treasure 6CA7/EL34 and the KT120s surpassed them in all ways as well).

[Steve]

Right, for a given set of conditions, the KT-120 will provide nearly the exact same output power as
the KT-90 or KT88s. However, three advantages do occur.

1) With higher plate voltage and idle current, more output is available since a higher plate dissipation
is available with the KT-120. However, it may take a slightly different OPT ratio to realize
the extra power.

2) In class A design, higher dissipations are possible and therefore higher power output is available
with the KT-120.

3) With higher plate dissipation, the tube can be run more conservatively in existing designs.

I also wondered about the sonics since on another forum, the HD (and probably IM) distortion
was measured as higher. However, evidently the sonics are very good.

Cheers.

[DaveC113]

They seem like good candidates for a pp amp, most people seem to like them better than kt88s. Not so sure about using them for a set amp though, has anyone tried it?

[richidoo]

I wonder if it will work in SimpleSE!   

[Steve]

I think it might be wise to consider a few areas before substituting.

1) Filament current is approx. 1.9 amps maximum, while KT88 is approx 1.6-1.7 amps.

2) Grid circuit resistence is different.

Fixed Bias  KT88 is 100k max.    KT120 is 51k maximum, might check your rig first.

Self Bias    KT88 is 220k             KT120 is 240k  so very similar

3) Transconductance appears to be close, 11-12k for KT88 VS 12.5k for KT120 under
similar conditions.

Conditions appear similar, but might double check. So bias setting should need
minimal adjustment, if any.

Data sheet shows higher distortion, but individuals seem to like the sonics.

Cheers.

[rpf]

Data sheet shows higher distortion, but individuals seem to like the sonics.

Cheers.

A customer service person at VAC told me that the KT120s could not be used in their (out of production) PA100/100 and that they are sticking with the KT88 in their amps because it is more linear, more accurate.

I have never heard KT88s sound as linear (and musical) as they do in the VAC (KT88) amps I've experienced, so obviously sonic comparisons of the two tube types may vary from amp to amp. Dynamics, headroom and soundstage size will probably always favor the 120s however.

[beanstocks]

Hello.  My twin mono block W6M modified has run the gamut of American KT88/6550 but in the end have settled on Genuine GEC Gold Lions.  The last switch off a year ago was with a matched quad of KT 120s of Russian manufacture I believe.  They boasted higher power and better high end but my results were a bit of disappointment.  Ran the tubes 80 hours before I settled to some critical listening.  There was a bit of harshness or hardness some would say, in the upper registers.  Cymbal finishes were not as clean and definitive and some "air" missing.  The mids were a bit sterile and had less bloom than old USA stock and GECs.  Bass, however was superb--clean, strong, Ray Brown's double bass was there in the room.  After another 4-5 days I switched back to GLs, happily.  Hope this helps.   Ron

[mgsboedmisodpc2]

from stereophile
"Fig.5 repeats the measurements with the amplifier fitted with KT120 output tubes, each biased to the same 35mA. By comparing figs. 5 and 4, you can see that while the KT120s don't allow the amplifier to deliver any more power at clipping—except into 2 ohms, when it delivers 120W (14.7dBW) at 1% THD—the Titan Atlas Magnum is more linear below clipping with KT120s than with KT90s."

and

"Erick Lichte very much liked the sound of Rogue Audio's Titan Atlas Magnum, especially with KT120 tubes. Though I must admit to some disappointment with the amplifier's lack of high-frequency linearity, in this respect it is no worse than the original EL34-equipped "

so go for the KT120 if you are looking for greater linearity

[rpf]

from stereophile
"Fig.5 repeats the measurements with the amplifier fitted with KT120 output tubes, each biased to the same 35mA. By comparing figs. 5 and 4, you can see that while the KT120s don't allow the amplifier to deliver any more power at clipping—except into 2 ohms, when it delivers 120W (14.7dBW) at 1% THD—the Titan Atlas Magnum is more linear below clipping with KT120s than with KT90s."

and

"Erick Lichte very much liked the sound of Rogue Audio's Titan Atlas Magnum, especially with KT120 tubes. Though I must admit to some disappointment with the amplifier's lack of high-frequency linearity, in this respect it is no worse than the original EL34-equipped "

so go for the KT120 if you are looking for greater linearity

Interesting, as I don't hear any significant problem in the high frequencies with the KT120s. They were definitely more linear sounding in the Cronus Magnum than any other tubes I've tried.

KT90s were a disappointment: lean sounding. I also tried NOS GE 6550s that were very smooth and refined, with a holographic mid-range, but they were much smaller scaled and had  a recessed bass compared to the 120s. The 120s threw a larger soundstage, had much greater dynamic range and had more weight and density as well.

[Ericus Rex]

Thank you all.

Beanstocks, I should hope that the original GECs would sound better than anything else available.  But did you compare the KT120 with any current production KT88?

I also haven't heard of anyone complaining about the KT120s high frequency distortion in actual use.  Maybe it looks bad on paper but is inconsequential in use.  Roger Modjeski of Music Reference (who I respect tremendously) is also impressed with the tube and this says a lot.

The Stereophile measurements are interesting but not really pertaining to my OP as the comparison is with the KT90 (a slightly beefier sounding EL34 in my amp).  Also I am more concerned with the sound of the two and not concerned with their plate dissipations.

I see some KT120s in my future!  And they're well under 1/2 the price of the Fuller and Psvanes!

Keep the comparisons coming!