Sonic Comparison between New Tung Sol 6550 vs KT120 vs KT150

[gadget73]

The reason i bought my kt120 when i did, they cost less than a kt88 or 6550. Not by much, maybe 5 or 10 a tube.


As for linearity they do have a bobble down in the low current zone that is worse than a kt88 curve set so i believe that statement. Its reminiscent of the old school "tetrode kink" that the KT series don't really have, so possibly the beam plates or grid alignment is imperfect.

 

[Joe Dawson]

@arts,
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..?

Thank you Kward. Some information concerning TS KT120s sounding different than the TS 6550s in the same circuit, same system.
That is helpful to me.

keep on trucking

joe

 

[Joe Dawson]

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.

It is not surprising to me. Let's suppose 20db of negative voltage feedback. That is a 10 to 1 ratio in gain and
variance in other parameters. That is not a complete nullification of differences.

10db of feedback allows even less nullification, thus more easily perceived.

Currently, in the "lab", many individuals who visit can identify sonic differences of 1 part in 4,100,000. That is approximately
-132db from the fundamental. There are different ways, such as a 12pf cap across a 47ufd in the speaker crossover, same
resistor changes etc.

Not surprising that sonic differences exist between components, with the same factory spec, as well.

keep on truckin

joe

 

[Joe Dawson]

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

Which Sovtek 6550? There have been many variants.

Good question Art. Mine are the black base from yesteryear. are yours the newer metal
base types?

 

[BmWr75]

TS 6550 quad came today. Listening to them now.

 

[arts]

Good question Art. Mine are the black base from yesteryear. are yours the newer metal
base types?

I have used every model 6550 from Sovtek, WA through WE. Each version is somewhat different in construction, performance and reliability.

The model with the plastic base is the WD version. I don't think those were produced for very long, as most amplifiers with 6550's use the base clamps that require the metal bases.

 

[Joe Dawson]

I have used every model 6550 from Sovtek, WA through WE. Each version is somewhat different in construction, performance and reliability.

The model with the plastic base is the WD version. I don't think those were produced for very long, as most amplifiers with 6550's use the base clamps that require the metal bases.

Thanks for the info Art.

 

[BmWr75]

I bought a quad of Tung Sol 6550s because of interested generated in this thread. Sat down today to listen to them in a PrimaLuna Dialogue Two amp driving Caladan open baffle speakers. They sounded dull on the top end, boring even. Pulled them and installed sold some vintage RFT dimple top EL34s. The sparkle is back. YMMV

 

[Brice]

You may need to give them sone time to break in. I had the same experience with GL KT77.

 

[automojo]

Last couple months I ended up dumping my Primaluna gear in favor of a Rogue Atlas iii Magnum, and a Atlas iii DARK. In the near future I plan on revisting the KT-120's. I didn't like them in either Prima Luna. However, as I have read in a few threads concerning this tube is they sound better with a higher bias setting (.45ma). EL@ Stereophile also seems to agree on his review of the Rogue Titan Atlas Magnum, finding .45ma the ideal setting.

Rogue Audio Titan Atlas Magnum power amplifier | Stereophile.com

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www.stereophile.com

 

[Brice]

Do you know the plate voltage your amp is operating?
At 45mA, the kt120 is most likely cold biased, almost too much to sound good.

 

[automojo]

Do you know the plate voltage your amp is operating?
At 45mA, the kt120 is most likely cold biased, almost too much to sound good.

Not sure, but would assume it’s the same as the Titan Atlas Magnum.
I’m thinking in the Stereophile review if it would’ve sounded like crap I don’t think he would’ve made a point of putting it in the article.
But I could ask Rogue.
I have not tried it yet, it was a comment on what I read in a few places.
I like my KT88’s and KT66’s so far, no need to roll yet.

 

[Joe Dawson]

I bought a quad of Tung Sol 6550s because of interested generated in this thread. Sat down today to listen to them in a PrimaLuna Dialogue Two amp driving Caladan open baffle speakers. They sounded dull on the top end, boring even. Pulled them and installed sold some vintage RFT dimple top EL34s. The sparkle is back. YMMV

That is interesting. Might give it more time to break in. When I was given an octet of new Tung Sol 6550s some years ago,
I just tried them now and they were nearly as bright as the sun vs other brands. I demagnetized the TS and most of the
brightness went away. I wonder if they changed sonics over the years in their designs?

keep on truckin

joe

 

[oldflame]

Do you know the plate voltage your amp is operating?
At 45mA, the kt120 is most likely cold biased, almost too much to sound good.

According to a ten-year-old call to Rogue, my 2015 Atlas Magnum has 585 volts on the plates ... unless my memory has lost more than a few volts. If that's correct, do you still feel that 45mA is too "cold"? Rogue sends it from the factory set at 35mA. OTOH, some use the 120's at 60 or more mA, but I don't know at what plate-voltage.

 

[a_retent]

If that's correct, do you still feel that 45mA is too "cold"? Rogue sends it from the factory set at 35mA. OTOH, some use the 120's at 60 or more mA, but I don't know at what plate-voltage.

I have a pair of Audio Research vm220 PP monoblock amps that originally came with 6550 tubes factory installed. Prior to my ownership TS kt120 tubes replaced the original 6550s. I will not speculate on the sonic differences between the 2 in my specific application because I wasn't afforded the luxury of having 2 complete sets of tubes to compare, 16 tubes per set, 32 total.



I will say that when I contacted ARC about using the kt120 tube, the service manager / repair tech confirmed the 120 was most acceptable and they should be biased at the same 65mA as the 6550s were. He did say this particular amp would not function properly using the kt150 tube. Based on that information I would have reason to believe 35-45mA may be a bit low for this tube to perform well.

 

[Brice]

585V plate voltage @ 45mA gives you a KT120 working at 44%.

Still cold.

65mA from ARC gets you a 64.3% plate dissipation (60W), which is more like a normal usage.

I am guessing that the power supply will suffer from higher B+ demand than 45mA, to get the KT120 going at a higher plate dissipation.

It is often the case.

I had the same problem with one amp which had 6550 tubes, switch to KT120, but the PS was complaining at the "normal" KT120 bias level 70%. 65mA was the max I would set it, and has run without issue for a few years now.

Going to a KT150 is dangerous for an amp not designed for it as the heater current is much higher (2A Vs 1.6A). Could be a problem for the PT.

 

[oldflame]

Thanks Brice and a-retent, your replies confirm other, usually reliable, info I've read elsewhere. Rogue had mentioned that some attention was given to improving the B+ supply beyond previous Atlas amps. I don't know if any changes were made since 2015. IIRC Stereophile Atlas Magnum reviews were quite favorable and I don't recall the bias being adjusted beyond the factory setting. Maybe the cold bias is "good enough" and with the amp's particular circuit, and component values, raising it will only make a small improvement. Of course, I'm only guessing about that.

Interesting topic. I wonder at what point reliability might become an issue? Rogue claims about 3000 hours can, typically, be expected for output tube-life. Apparently, new production tubes don't match NOS for life, so maybe a "cooler" bias will help extend the KT-120's usefull existence. Had the 120's been manufactured back in the Olden Days, perhaps they'd have closer to 5000 hours of life.

 

[Brice]

Yes that's correct.

Also people makes the mistake thinking using a bigger tube will increase the wattage out of the amp, which is untrue.

IMO, using a KT120 instead of a KT88/6550 is a good move if your amp supports it safely, making the power tubes last much longer at that dissipation level.
Sound wise, the KT120 is excellent, with better bass. It's a super KT88.
I have no experience with KT150.

 

[BmWr75]

I bought a quad of Tung Sol 6550s because of interested generated in this thread. Sat down today to listen to them in a PrimaLuna Dialogue Two amp driving Caladan open baffle speakers. They sounded dull on the top end, boring even. Pulled them and installed sold some vintage RFT dimple top EL34s. The sparkle is back. YMMV

Reinstalled these Tung Sol 6550s and tried to listen to them yesterday while an audio friend was visiting. There was so much noise coming from the amp it sounded like we were listening to a scratched up vinyl record. First changed out the 12AX7 drivers. No change, still noisy. Then changed out the 6550s for some 6CA7s, noise gone. Conclusion, the 6550s must be noisy in my amp anyway.

 

[automojo]

Eventually I found the Atlas Magnum III (now both are Dark Version) simply sounds better with the KT120, vs KT88. They never came with 6500's-the first ones EL34/KT77.
The KT120's are way more dynamic then KT88's. The mid are way better-EL34 like, and the high are smooth and grain less. As far as the distortion curve? Who knows....does not seem to matter much here.........