[mca]

If you had your choice between these two in an amp, which one would you choose and why?

[FullRangeMan]

If you had your choice between these two in an amp, which one would you choose and why?

Imo current production of Chinese 6550 are modeled to guitar amps(hi distortion), which the musicians call harmonics.

[rpf]

I've had both in my Cronus Magnum (and had 6550s in a couple of amps before that). I prefer the 120s: they are more extended top and bottom, while retaining a full mid-range. They produce a larger soundstage and are more dynamic, if not quite as refined. They, IMO, are superior overall to current 6550s. NOS GE 6550s have a harmonic richness and three dimensionality of images that is unbelievably seductive, but they fall short of the 120s in the other areas above. And are now very expensive, if you can find them.

If you don't need that much power, however, my favorite tube is the KT66. To me it has a more even frequency balance, and a greater purity of tone, transparency, coherency, and refinement than any of the other pentode/beam pentode/kinkless tetrode tubes. The Genalex KT66 reissue is superb.

[dBe]

I've had both in my Cronus Magnum (and had 6550s in a couple of amps before that). I prefer the 120s: they are more extended top and bottom, while retaining a full mid-range. They produce a larger soundstage and are more dynamic, if not quite as refined. They, IMO, are superior overall to current 6550s. NOS GE 6550s have a harmonic richness and three dimensionality of images that is unbelievably seductive, but they fall short of the 120s in the other areas above. And are now very expensive, if you can find them.

If you don't need that much power, however, my favorite tube is the KT66. To me it has a more even frequency balance, and a greater purity of tone, transparency, coherency, and refinement than any of the other pentode/beam pentode/kinkless tetrode tubes. The Genalex KT66 reissue is superb.

KT66 +1 on the Genelecs... New or unobtanium.

From guitar amps to stereo audio reproduction they have a harmonic series and integration that just pushes my button.

[marvda1]

where do the kt 90's fit sound wise?

[JLM]

JJ 6550 kicks Tug Sol KT120 butt in my Prima Luna Dialogue Premium Integrated. 

The KT120's sound no better than my solid state gear (which ain't bad stuff, but clearly worse than EL34, KT66, or KT77).  Out of all the above tubes, the 6550 are my favorite.  Note that except for the KT120's, all tubes are cryo'd.

Note also that the amp has auto-biasing, which ends up negating most of differences between output tubes.

[mca]

Interesting, one vote for KT120 AND ONE FOR 6550 

[rpf]

JJ 6550 kicks Tug Sol KT120 butt in my Prima Luna Dialogue Premium Integrated. 

The KT120's sound no better than my solid state gear (which ain't bad stuff, but clearly worse than EL34, KT66, or KT77).  Out of all the above tubes, the 6550 are my favorite.  Note that except for the KT120's, all tubes are cryo'd.

Note also that the amp has auto-biasing, which ends up negating most of differences between output tubes.

How long have you had the JJs? From what I've read their power tubes aren't that reliable.
In what way do they sound better than the KT120s?

The Cronus has manual bias but I don't know how much that matters; although different tube types have sounded distinctly different in all of the amps (all manually biased) I've had. Why does auto bias negate much of the difference between tube types?

[jupiterboy]

Winged C 6550s are good in my amp, but the KT120 is better on several counts, so it wins.

[dminches]

I would choose NOS Tung Sol 6550s over any new production tube.

[paul79]

Neither get my vote for home audio. I prefer KT88's, particularly Penta Labs.

[rpf]

Btw, the KT66s will put out just a bit less wattage than 6550s. Edit: most amps run the latter at 25-35 watts but some manufacturers run them significantly higher.

NOS Tung Sols at what price?

The Penta Labs KT88SCs are quite good but seem to be unavailable now.

The excellent Winged C 6550s are no longer made. Upscale Audio still has them for now, at $70 apiece.

[Servingthemusic.com]

If you had your choice between these two in an amp, which one would you choose and why?

KT120. It is not even close.

[rpf]

where do the kt 90's fit sound wise?

I've never heard the no longer made EI. I did try the Electro Harmonix. I don't remember precisely how they sounded (a tad lean IIRC) but do remember that I didn't see the point of them. I preferred the Penta KT88s and, by a large margin, the KT120s as well.

[Octadyn]

where do the kt 90's fit sound wise?

I can't speak for the EH KT90's but I have Ei KT90's type II and III.  For me it's the best of the bunch. Why? Because it's the only output tube that sounds real good with either Dynaudio C1 Sig or Raidho D1/D2. With the C1's the original TS 6550 solid black plate wins hands down. KT120's are the worst. Punchy yes - good extension but very 'shouty'.  With the D1 or D2 the TS 6550 are too rolled off in the highs and too sluggish in the lows. KT120's with Raidho is better but still not right. The Ei KT90 is very linear and balanced the best from top to bottom.

Of course this my personal opinion on the sound I like. Never tried the TS 6550 re-issue. My amp came with SED 6550 winged 'C'. Nice and linear but dry sounding.

[rpf]

A correction: the Penta KT88SC is available here: http://www.thetubestore.com/Tubes/KT88-Tube-Types/Preferred-Series-KT88

[ElliottStudio]

I have tried the 120's in my amp and preferred the 6550's; the 120's didn't sound as refined - they had punch and a certain 'wow' factor but the 6550's won out in the long run. This amp was designed to run 6550's though..

I did however build an amp specifically for the KT120's for a client and that amp sounded great. The difference being higher plate voltage, higher bias current and voiced with different caps.

So- I think it is really amp / circuit dependent. Just plugging 120's into an amp designed to run 6550's or KT88's won't get you much except for extended tube life. If manual bias, increasing the bias current can make a difference. YRMV.

[Freo-1]

I always liked the GE 6550A.  Very stout, clean sounding tube. 

I thought the KT-120 has plate curves that were not so not.  The 6550 should be more linear.