Sonic Comparison between New Tung Sol 6550 vs KT120 vs KT150

[oldflame]

Sorry if this is too OT, but when did tube "rolling" become a practice with audiophiles? IIRC, it was maybe the 1990's, or even later, when I first read about it and seems to have become more prevalent since ... especially here at the AK. I suppose it could have started in the 70's, after the initial demise of vacuum tubes.

 

[opnly bafld]

@Joe Dawson

KT120 dissipation

Just finished up a pair of KT120 monoblocks using tungsol tubes, that sound amazing BTW, but after listening for about an hour I notice the left plate of both tubes (Keyway is facing forward in the amp, ) have a little red glow deep in the groove of the folded plate area. It's not the whole side...

audiokarma.org

 

[opnly bafld]

Sorry if this is too OT, but when did tube "rolling" become a practice with audiophiles? IIRC, it was maybe the 1990's, or even later, when I first read about it and seems to have become more prevalent since ... especially here at the AK. I suppose it could have started in the 70's, after the initial demise of vacuum tubes.

I assume this thread is about finding a good new production tube that performs closer to nos 6550 tubes that are getting more rare and super expensive. Perhaps the old tubes are just plain getting worn out and need to be replaced.

 

[BmWr75]

Thank you BmWr75. Yes, I understand there are a few hours difference, but at least some sort of comparison. Can you let the new
tubes run for a few hours, even idle, just to get some time on them?

Have there been any problems with the 10 year old TS KT120 tubes? I ask because some years ago the JJs would cherry plate at
~80% plate dissipation, maybe less, that could affect results?

Much appreciated and I am sorry that I was rather rough.

joe

No problems at all with the KT120s. The PrimaLuna has an adaptive auto bias circuit.

 

[arts]

This is off topic, as I did not have available any TS 6550's for comparison at the time of my testing. Therefore, if anybody is offended by this post or considers it to be too far "OFF-TOPIC" to be acceptable, I am sure that the moderators will be very happy to delete this content.

I have tried the KT120 in three of my amplifiers, all of which are Audio Research Corporation products. All required nothing more than the bias to be adjusted for the different type.

The 6550's that I have used/rotated through these amplifiers are GE, Sylvania, Sovtek and Svetlana. They all perform about the same, vis-a-vis sonics and electrically.
I firmly believe that the Tung Sol is just a re-branded Sovtek, perhaps with better QC, so maybe close enough to a TS to count here?

VS110; this model can accept either 6550 or KT120 types without issue.

D70 MKII & D76A: these two were not intended for the additional heater current required for the KT120, although the heater voltage did remain on-spec, and I was comfortable running them with the KT120's for a couple of weeks of listening/testing to form an opinion. The power transformers ran slightly warmer.

My conclusions:

1: All three amplifiers bench tests were so close as to be inconsequential.

2: For whatever my sonic perceptions are worth, I did not like the KT120 in any of the amplifiers. In fact, I much preferred the 6550, regardless of brand.
Which really contradicts my initial personal expectation bias of great things from the KT120...

Just my 2¢, feel free to delete

 

[oldflame]

I assume this is about finding a good new production tube that performs closer to nos 6550 tubes that are getting more rare and super expensive. Perhaps the old tubes are just plain getting worn out and need to be replaced, what should I buy that won't disappoint?

Well, sort of, opnly bafld. I do have a couple amps that use 6550's but have room to install the taller KT-120's so I'm not sure what I might do. Certainly I wouldn't want less than the 1970's GE brand performance and KT-120's might just be insurance against poor, newer, 6550's-- if I want to buy Russian KT's. The Dyna MkIII & Sunn 200S both use the Dyna 430 transformer and, I believe, should handle the added heater current.

Until the last ~35 years, I hadn't been aware of choosing particular tube brands for best quality. I wasn't as deeply into tube-electronics as some other were before the 1990's. I was curious about when tube aficionados began more carefully choosing there poisons.

 

[opnly bafld]

@oldflame

I edited my post above, I was referring to the possible reason for this thread, not your post.
Sorry

Might be a question deserving its own thread if you are really curious enough.

I'm not a tube roller, so I don't pay much attention to it.

 

[oldflame]

@oldflame

Might be a question deserving its own thread if you are really curious enough.

Good point; I'll have to decide how seriously curious I am.

arts, what do you prefer about the 6550 sound? It's interesting knowing what others hear that I might not.

 

[arts]

arts, what do you prefer about the 6550 sound? It's interesting knowing what others hear that I might not.

^^^
@arts

That would be very, very, difficult to describe.

First, I have been a musician and been surrounded by other musicians for most of my life, and my musical tastes are extremely eclectic. I listen to electric and non-electric in equal measure, from chamber music all the way up to Humble Pie front row center (although these days I do need a doctor ).
I have likely attended more live performances than most people have listened to albums, so my appreciation for the delicacies of many instruments is rather well developed.

I cannot identify what makes the 6550 preferable to the KT120.

But, I can identify what I dislike about the KT120; I find that everything sounds compressed, closed in, one-dimensional, lifeless. It actually reminds me of those amplifiers from the 1970's with the 0.000001% THD ratings, where the mega-dB's of negative feedback sucked all of the life out of the music.

 

[Bill Ferris]

This is off topic, as I did not have available any TS 6550's for comparison at the time of my testing. Therefore, if anybody is offended by this post or considers it to be too far "OFF-TOPIC" to be acceptable, I am sure that the moderators will be very happy to delete this content.

I have tried the KT120 in three of my amplifiers, all of which are Audio Research Corporation products. All required nothing more than the bias to be adjusted for the different type.

The 6550's that I have used/rotated through these amplifiers are GE, Sylvania, Sovtek and Svetlana. They all perform about the same, vis-a-vis sonics and electrically.
I firmly believe that the Tung Sol is just a re-branded Sovtek, perhaps with better QC, so maybe close enough to a TS to count here?

VS110; this model can accept either 6550 or KT120 types without issue.

D70 MKII & D76A: these two were not intended for the additional heater current required for the KT120, although the heater voltage did remain on-spec, and I was comfortable running them with the KT120's for a couple of weeks of listening/testing to form an opinion. The power transformers ran slightly warmer.

My conclusions:

1: All three amplifiers bench tests were so close as to be inconsequential.

2: For whatever my sonic perceptions are worth, I did not like the KT120 in any of the amplifiers. In fact, I much preferred the 6550, regardless of brand.
Which really contradicts my initial personal expectation bias of great things from the KT120...

Just my 2¢, feel free to delete

As to you`re concern with the higher filament requirements of the KT-120, and I`m assuming KT-150`s (I have no knowledge of their filament draw) yet even higher I/f needs was the first concern that crossed my mind when I originally first came upon this thread some time earlier last week.

Just an observational comment, that is all, from my technical concern.

If the OP`s home constructed amp initially has plenty of filament current headroom to handle the 120/150`s higher filament current without transformer current draw stress, will then should be no concerns for the power transformer`s long term heath.

I would be hesitant to try 120/150 due that concern alone with tube rolling them with my own D-76A, as it seems quite happy with the matched GE 6550 currently residing in it, and if I ever need to replace the outputs in the future, probably go with new manufacture 6550, or KT-88s and would be the route I`ll go.

 

[oldflame]

But, I can identify what I dislike about the KT120; I find that everything sounds compressed, closed in, one-dimensional, lifeless. It actually reminds me of those amplifiers from the 1970's with the 0.000001% THD ratings, where the mega-dB's of negative feedback sucked all of the life out of the music.

What if ... the 120 has a microscopic R/C connection between G1 and anode for self-induced feedback? I haven't slept enough, lately.

 

[arts]

What if ... the 120 has a microscopic R/C connection between G1 and anode for self-induced feedback? I haven't slept enough, lately.

I think that would be positive feedback; wouldn't that make things dynamic, open, deep and lively? (I don't sleep at all anymore.. )

 

[oldflame]

After my nap I had realized my mistake. It's good you pointed that out because I could've misled or confused someone first dipping their toes into this sport.

 

[kward]

@arts,
I also have tried KT120s in amps built/tuned for 6550s (in my case my long standing reference CJ Premier 11), and I did not like the sound of that amp with KT120s. On the other hand, amps that were tuned for the KT120s sounded better to me than that same amp running Tung Sol new production 6550s.

I would have thought that in a global feedback Push Pull topology I would not have been able to discern a big difference. Go figure..?

 

[dcgillespie]

All triodes in fact do have a feedback path between G1and the anode. It’s negative feedback, which would be the same case if the KT120 had a “microscopic R/C connection between G1 and anode” unless I’m missing something here……which is always possible…..

Dave

 

[arts]

All triodes in fact do have a feedback path between G1and the anode. It’s negative feedback, which would be the same case if the KT120 had a “microscopic R/C connection between G1 and anode” unless I’m missing something here……which is always possible…..

Dave

Sarcasm....

 

[arts]

@arts,
I also have tried KT120s in amps built/tuned for 6550s (in my case my long standing reference CJ Premier 11), and I did not like the sound of that amp with KT120s. On the other hand, amps that were tuned for the KT120s sounded better to me than that same amp running Tung Sol new production 6550s.

I would have thought that in a global feedback Push Pull topology I would not have been able to discern a big difference. Go figure..?

The Premier 11 is an excellent amplifier, and the output transformers are incredible. I've always wanted something from that range, but around here they get snapped up instantly.

I agree that theoretically, there should be no difference in a feedback amplifier. But as we all know, oftentimes theory goes out the window when practice rears it's ugly head.

 

[Joe Dawson]

"I firmly believe that the Tung Sol is just a re-branded Sovtek, perhaps with better QC, so maybe close enough to a TS to count here?"

I have both the Sovtek and TS, and they sound quite different in my monoblock amps.

One interesting note; from a poster on another string stated that the TS KT 120 appears to be a 6550 with additional external angled plates welded to provide higher plate dissipation. That would be interesting development. IF that is the case, then the specs for the TS 6550 and KT 120 are
essentially the same.

As far as red plating on one side of the plate; the cathode should be centered with respect of grid, screen, beam electrodes
and plate.

Especially with respect to the grid and screen.

keep on truckin

joe

 

[arts]

"I have both the Sovtek and TS, and they sound quite different in my monoblock amps."

Which Sovtek 6550? There have been many variants.

 

[GordonW]

I'm tempted to get a couple of TS KT120s, and send them over to Dave Gillespie, so he can test them to see if they perform well, relatively to the new-production Gold Lion KT88s. Comparing the KT150s would be interesting, as well. I've been told by a very well regarded high-end amp designer, that neither the KT120 or KT150 is as linear (as indicated by the plate curves) as the KT88.

Of course, as difficult as TS KT120s have been to get recently, that might be a pretty daunting task, right now.

Regards,
Gordon.