KT120 vs 6550 / KT88

GT Audio Works · « **on:** 17 May 2013, 11:47 am »

Anyone have experience with substituting KT120's in their amp ?
Thinking of purchasing a 6550/KT88 amp that can run KT120's.
I called Audio Research interested in subbing tubes for a Classic 60...
they advised against it, the amp circuitry is not designed to support the higher voltages and currents the tube requires.
They say their older VS 110 can be upgraded.
I have not decided on a manufacturer yet..maybe Quicksilver V4 or VTL.
My primary reason for wanting the KT120 is they are said to be a more robust tube made for audio application and their replacement cost is similar to the 6550/KT88.
Greg

roscoeiii · « **Reply #1 on:** 17 May 2013, 12:28 pm »

Does depend on if the amp can handle the KT120s. Think it depends on the transformers mostly. I really like my Rogue Stereo 90 with the KT-120s.

GT Audio Works · « **Reply #2 on:** 17 May 2013, 12:46 pm »

Quote from: roscoeiii on 17 May 2013, 12:28 pm

Does depend on if the amp can handle the KT120s. Think it depends on the transformers mostly. I really like my Rogue Stereo 90 with the KT-120s.

Forgot about Rogue...How would you describe the sound of Rogue amps as opposed to ARC or Quicksilver..anyone have any input ??

Maritan · « **Reply #3 on:** 17 May 2013, 01:20 pm »

I have heard the Rogue Cronus Magnum. It was at a dealer in a well set up room. I could have stayed there for hours listening to it. Wide and deep soundstage. Great imaging. I just loved it. That was the first well set up tube amp I had heard. It isn't a direct A/B comparison, but hope that helps.

I have an older model VTL ST-150 now. Apparently they are so particular that they advice to use only 6550s, not even KT88s. SteveFord hopefully will chime in since he has a lot more experience with them. Their service is also supposed to be bad. Again, Steve will be able to give you a lot more info regarding that.

Good luck!

medium jim · « **Reply #4 on:** 17 May 2013, 01:52 pm »

I have a ARC VS-110 and I called Audio Research and s/w Kal and he recommended 6550's and modern ones as the old or NOS ones dissipate only 35 watts whereas the new production 42 and they were designed with that in mind. He said that I could go with KT88' and even KT120's, but would lose some speed and dynamics....it would be a very warm tube sound....

I opted for 6550's and couldn't be more pleased.

Jim

GT Audio Works · « **Reply #5 on:** 17 May 2013, 02:21 pm »

Quote from: medium jim on 17 May 2013, 01:52 pm

I have a ARC VS-110 and I called Audio Research and s/w Kal and he recommended 6550's and modern ones as the old or NOS ones dissipate only 35 watts whereas the new production 42 and they were designed with that in mind. He said that I could go with KT88' and even KT120's, but would lose some speed and dynamics....it would be a very warm tube sound....

I opted for 6550's and couldn't be more pleased.

Jim

The ARC VS115 sounds like an amp I want to try...I have tried a ARC classic 60 and sounded great...plenty of power.

medium jim · « **Reply #6 on:** 17 May 2013, 02:55 pm »

Quote from: GT Audio Works on 17 May 2013, 02:21 pm

The ARC VS115 sounds like an amp I want to try...I have tried a ARC classic 60 and sounded great...plenty of power.

The VS-115 evolved from the VS-110 and uses a different front end tube, 6H30 and is biased for KT120's which gives it about 10 more watts per channel, all other things being equal. I have listened to one with a pair of Sonus Faber Amati's and it was might damn good.

I like Audio Research as they make rock solid audio gear that doesn't get old....

Jim

Ericus Rex · « **Reply #7 on:** 17 May 2013, 04:35 pm »

Quote from: GT Audio Works on 17 May 2013, 12:46 pm

Forgot about Rogue...How would you describe the sound of Rogue amps as opposed to ARC or Quicksilver..anyone have any input ??

I have owned three Quicksilver amps; the 8417, the Silver 60s and I still own my GLA. I also own a Rogue Stereo 90 with Super Mag upgrade. The Quickie sound is very neutral with no major flaws anywhere. I find their house sound to be a little bland personally. The GLA is the only one I've kept for any length of time (I guess 6 years now). It was their entry level amp when new but I find it very satisfying. Both the 8417s and the Silver 60s were sold within a year of taking ownership. I was just looking for a bit more tube magic and 'ZIP' (Silver 60s) and more authority in the bass (8417s). I think I get both of those qualities with my Rogue Stereo 90. I'm very happy with the amp but I haven't yet tried the KT120s in it. Very soon, I hope. I had a slight issue with the 8417 once (don't remember exactly what happened, burnt resistor or similar) but I never had a single issue with the Silver 60s, GLA or Rogue amp...knock on wood!

GT Audio Works · « **Reply #8 on:** 17 May 2013, 05:28 pm »

Thanks for the info,, I am going to try to beg borrow or steal a few amps to hear in my system..namely the Rogues, Quicksilver v4's and the ARC VS115. Greg

Ericus Rex · « **Reply #9 on:** 17 May 2013, 07:14 pm »

Don't forget the Music Reference RM-200!

GT Audio Works · « **Reply #10 on:** 17 May 2013, 07:50 pm »

Quote from: Ericus Rex on 17 May 2013, 07:14 pm

Don't forget the Music Reference RM-200!

Yes...Must add it to the list...I have heard that one and it is also very good.

SteveFord · « **Reply #11 on:** 17 May 2013, 10:06 pm »

I've had VTLs for many moons but I'm sure that they'll say KT120s would require modifications.
They might be able to put together an upgrade package for you.

I just had a thought: what about Bob Carver's new amps? You've heard them with your speakers and they have KT120s.

jarcher · « **Reply #12 on:** 18 May 2013, 01:34 am »

I've thought about this in considering buying an older Conrad Johnson MV751A1 from my tube tech that uses 6550s & was curious about running KT120's on it. He seemed to feel there was no problem using KT120's. To get the full power of the KT120's the B+ voltage (?) would have to be raised. Aside from how they sound, another reason I've heard that KT120's are preferable is longevity - i.e. whereas depending on the design a 6550 or KT88 tune in amp may be run close to flat out (e.g. a Mcintosh MC275), a KT120 has more power handling so you don't have to run them as "hot" to their max potential to get the same output.

Anyway - talking here a bit beyond my personal knowledge, but just passing along what folks more knowledgeable than I have told me.........

DustyC · « **Reply #13 on:** 18 May 2013, 05:10 am »

Quote from: jarcher on 18 May 2013, 01:34 am

I've thought about this in considering buying an older Conrad Johnson MV751A1 from my tube tech that uses 6550s & was curious about running KT120's on it. He seemed to feel there was no problem using KT120's. To get the full power of the KT120's the B+ voltage (?) would have to be raised. Aside from how they sound, another reason I've heard that KT120's are preferable is longevity - i.e. whereas depending on the design a 6550 or KT88 tune in amp may be run close to flat out (e.g. a Mcintosh MC275), a KT120 has more power handling so you don't have to run them as "hot" to their max potential to get the same output.

Anyway - talking here a bit beyond my personal knowledge, but just passing along what folks more knowledgeable than I have told me.........

I used to have a pair of C-J MV75's. They run those 6550s pretty hard. Your tech mentioned that the B+ would have to be raised. My amp's power transformers ran pretty hot with the 6550's. The increased current draw of the 120's might be a little much. Have the tech nearby when you plug those 120's in.

GT Audio Works · « **Reply #14 on:** 18 May 2013, 12:53 pm »

Sometimes what seemed a good idea.... in the cold light of reality and reason sometimes loses its appeal.
I wanted to try the KT120's due to their robust reputation, higher power output, sonics ( yet to be heard), longevity and similar price.
But I am finding out their application may be more limited than I wanted.
My two ultimate criteria for a tube amp are sonics and price. If this amp can use KT120's great, if not the standard output tube will do just fine.
Thanks for every ones input....Greg

avta · « **Reply #15 on:** 18 May 2013, 03:10 pm »

I own the Quicksilver Silver 88 monos. I have not owned another tube amp so I am unable to compare these with others. I use them with Harbeth Compact 7 speakers and a Shindo Aurieges-L pre along with an Anedio DAC1. I have had a few ss amps such as W4S ST500, Pass Aleph3, McIntosh MC252. The Silver 88's sound, to my ears, much more lifelike and lush. They have plenty of power and have so far been reliable. ( I have had them for about 3 yrs. ) In my view they are reasonably priced and are hand made in Stockton, California. They use point-to-point wiring and no circuit boards. As you may know they earned a Stereophile Class A rating. I have no connection with the company other than being a customer.

rpf · « **Reply #16 on:** 18 May 2013, 03:35 pm »

Quote from: GT Audio Works on 18 May 2013, 12:53 pm

Sometimes what seemed a good idea.... in the cold light of reality and reason sometimes loses its appeal.
I wanted to try the KT120's due to their robust reputation, higher power output, sonics ( yet to be heard), longevity and similar price.
But I am finding out their application may be more limited than I wanted.
My two ultimate criteria for a tube amp are sonics and price. If this amp can use KT120's great, if not the standard output tube will do just fine.
Thanks for every ones input....Greg

The Rogue amps will take KT120s without any problems. I've owned a CJ MV60SE and Quicksilver Mono 100s, and had a CJ LP66, McIntosh MC275 V5, Music Reference RM200, and VAC PA100/100 in my system and overall I'm more happy with my Rogue Cronus Magnum with the KT120s.

I'd lend it to you but it's already been shipped to my soon to be new home in FL.

EDIT: the Magnum versions of the Rogue amps will take KT120s.

DaveC113 · « **Reply #17 on:** 18 May 2013, 03:44 pm »

From my limited knowledge about them... I was looking into 120s but quickly abandoned the idea of using them in a SET amp... they should work fine in any amp made for a 6550/kt88 but the bias point won't be optimal so there won't be more power. Some amps designed for 6550/kt88 can be modified to have an ideal bias point for kt120s, others may not.

Fwiw, most people seem to like them so it's probably worth trying them out in a PP amp that is designed for them or can be modified for them.

roscoeiii · « **Reply #18 on:** 18 May 2013, 03:46 pm »

Quote from: rpf on 18 May 2013, 03:35 pm

The Rogue amps will take KT120s without any problems. I've owned a CJ MV60SE and Quicksilver Mono 100s, and had a CJ LP66, McIntosh MC275 V5, Music Reference RM200, and VAC PA100/100 in my system and overall I'm more happy with my Rogue Cronus Magnum with the KT120s.

I'd lend it to you but it's already been shipped to my soon to be new home in FL.

Not entirely correct. The cheaper Rogue tube amps need to be upgraded to Magnum status to take KT120s.

medium jim · « **Reply #19 on:** 18 May 2013, 03:48 pm »

In my case, I could have used KT88's without issues and even KT120's, but the issue to me was that Audio Research no doubt spent lots of time and money in R&D to figure how to make it sound its best with new production 6550's and why mess with that formula. As for changing the preamp/front end tubes, no biggie if I were able to....that is the only drawback is that it only accepts the 6N1P.

On the other tube amps I've owned, I did roll the driver/input tubes with nice results.

Jim