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Driving Kt-88

74.179.132.107
Posted on November 5, 2009 at 04:14:49
MillHouse1835@aol.com
Audiophile

Posts: 197
Location: South Carolina
Joined: March 19, 2007
 I would greatly appreciate any help on this question. What is the difference between driving KT-88's with 12ax7 types versus 6sn7's. Cary, Cayin and Audio Space all make 6sn7 driven amps, while Jolida and many others use 12ax7's. I'm getting ready to buy a KT-88 power amp. Even personal opinions are welcome. thanks

RE: Driving Kt-88, posted on November 5, 2009 at 18:29:21
Eli Duttman
Audiophile

Posts: 6155
Location: Plainsboro, NJ
Joined: March 31, 2000
 So, you want to possess a KT88 amp. Think very hard about acquiring a vintage Harman/Kardon Citation II and having it overhauled according to AA sponsor Jim McShane's method.

Fact, nothing in the commercial marketplace today has O/P transformers of the quality found in the Cit. 2. Superior "iron" and unique circuitry by a legendary master designer, Stu Hegeman, combined with some modern parts yields PERFORMANCE.

Eli D.
RE: Driving Kt-88, posted on November 6, 2009 at 09:03:41
catsimone
Audiophile

Posts: 17
Location: New York City
Joined: November 26, 2004
 Eli-
Could you explain the logistics required to own a McShane modded Citation II? Does one need to obtain one through ebay, etc. and send it to him to mod, or does he have any himself to purchase already modded? Also, assuming one has one, will he do the mods himself, or does he only sell kits for one to do it themselves?? I visited his website and only saw the kits for sale, with no mention of him doing the actual modding (or complete units for sale, for that matter). Thanks...

RE: Driving Kt-88, posted on November 7, 2009 at 14:45:37
Jim McShane
Dealer

Posts: 3405
Location: Chicago
Joined: January 13, 2003
Contributor
  Since: April 11, 2002
 Hello,

Since you asked... I sell the kits and occasionally complete refurbished amps (I have none right now).

If you don't want to do the work yourself I now have an authorized installer who can do a superb job of redoing your amp. If you can find a good "core" amp, we can whip it into shape for you. He uses my kits, tubes, and parts, and the amp is better than new when finished. It's guaranteed too!

Feel free to email with any questions you might have, I'll be happy to help.
RE: Driving Kt-88, posted on November 5, 2009 at 17:53:01
JimL
Audiophile

Posts: 3349
Location: New Mexico
Joined: November 24, 2002
 First of all, I don't think it's a good idea to focus on tube types as THE factor to use in choosing an amplifier - there are simply too many other technical variables involved, such as transformers, parts selection, etc. which can affect the sound.

Having said that, 12AX7 tubes are rarely used as DRIVER tubes because they are high voltage amplification, low current tubes, commonly running around 1 mA plate current, whereas power tubes generally need significantly higher current in their driver tubes to avoid high frequency distortion due to inadequate slew rate from current limiting. For example, Jolida actually uses 12AT7 and 6SN7 tubes as drivers in their KT88 amps, NOT the 12AX7 which is used as an INPUT tube. The only manufacturer that I know off hand that used them specifically as driver tubes was Jadis, and although their amplifiers had a good reputation for sonics, they started slew limiting around 5 kHz.

6SN7 tubes ARE frequently used as DRIVER tubes, commonly running at 5-10 mA plate currents. Other tubes that are used as drivers include 12AT7, 12AU7, 6DJ8, 6H30 and so on. They may be paired with higher voltage gain INPUT tubes such as 12AX7 and 6SL7, although 6SN7 and 6DJ8 tubes have also been used as input tubes.

IMHO, NONE of this should be used to determine what amplifier to buy, as the choice of tubes only one of many factors that are used by a competent designer. It would be equivalent to choosing a car based on whether it has a V8 engine or not, and ignoring everything else such as ride, handling, etc.

RE: Driving Kt-88, posted on November 5, 2009 at 09:47:52
Palustris
Audiophile

Posts: 251
Location: Cape Cod
Joined: September 12, 2008
 Think outside the 12AX7/6SN7 box. Get a good tube manual.

It's a sad day, but I guess a sign of the times..., posted on November 5, 2009 at 09:18:47
Allen Wright
Manufacturer

Posts: 4729
Location: Schaffhausen
Joined: January 31, 2002
 ...when junk designs from China are used as the reference to what tubes should be used in an amp.

Most of these amps have never been near a "designer" who thought, built, listened, rethought, rebuilt and relistened untill it SOUNDED fantastic.

Rather, consider the 60's US masters: Marantz, Harmon Kardon and MacIntosh if you want innovative designs, and to learn about tube choice.

Regards, Allen

Good to know that the 12AX7 was never used as a driver tube..., posted on November 6, 2009 at 09:25:18
Ivan303
Audiophile

Posts: 15825
Location: San Francisco
Joined: February 26, 2001
 in a PP amp until the Chinese arrived on the scene! ;-)


Ever look at the schematic of a Jadis JA-80 power amp?, posted on November 6, 2009 at 18:48:14
JimL
Audiophile

Posts: 3349
Location: New Mexico
Joined: November 24, 2002
 see link.

I don't think there are any amps that use the 12AX7 as a driver, posted on November 6, 2009 at 17:13:19
VynylTap
Audiophile

Posts: 1123
Location: USA - SouthEast
Joined: November 16, 2007
 tube, Chinese or not. They are used appropriately as INPUT tubes in Jolida amps, 12AT7's are the driver tubes.


"I'll play it and tell you what it is later..." - Miles Davis
Um....wrong. See inside., posted on November 6, 2009 at 18:46:12
JimL
Audiophile

Posts: 3349
Location: New Mexico
Joined: November 24, 2002
 Jadis JA-80 schematic. Check out the 12AX7 drivers for 4 KT88 tubes.

Um...okay...one, posted on November 7, 2009 at 09:24:36
VynylTap
Audiophile

Posts: 1123
Location: USA - SouthEast
Joined: November 16, 2007
 Man, I despise the use of "um" in a response - you may as well just not sugarcoat it and put, "Wrong, you dumbass..."

I did say "I don't think there are any". Not having been blessed with omnipotent knowledge of all amps ever manufactured I wasn't aware of the Jadis.

You have to admit it's an unorthodox design.


"I'll play it and tell you what it is later..." - Miles Davis
Ok, what about...., posted on November 7, 2009 at 11:12:29
JimL
Audiophile

Posts: 3349
Location: New Mexico
Joined: November 24, 2002
 wrong, filament breath! :-) Yeah, the Jadis is weird. That's what designed by ear will get you sometimes. I remember Martin Colloms tying himself in knots trying to explain why it sounded good and measured bad in TAS after HP raved about the JA-200 which IIRC used a 12AX7 to drive twice as many KT88s as the JA-80. Not to mention spacing the KT88s so close together that they overheated and failed. There's a phrase that describes this: incompetent engineering.

Hey! I kind of like "filament breath"!, posted on November 7, 2009 at 13:18:55
VynylTap
Audiophile

Posts: 1123
Location: USA - SouthEast
Joined: November 16, 2007
 ... I may have that put on my tombstone ...




"I'll play it and tell you what it is later..." - Miles Davis
RE: It's a sad day, but I guess a sign of the times..., posted on November 5, 2009 at 13:28:27
MillHouse1835@aol.com
Audiophile

Posts: 197
Location: South Carolina
Joined: March 19, 2007
 well then, Mr Wright, be specific. name names. who's good in todays arena?

I was specific., posted on November 5, 2009 at 16:24:00
Allen Wright
Manufacturer

Posts: 4729
Location: Schaffhausen
Joined: January 31, 2002
 If you want top design names today: 1/ VacuumState, 2/ BAT, 3/ Convergent, 4/ Walcott etc etc

And NOT in that order of imprtance - just four names I thought of that are well designed, some using fairly unusal tube like the 6H30 as the driver tube..

Regards, Allen

You might want to mention that YOU manufacture "Vacuum State" amps..., posted on November 6, 2009 at 17:07:57
VynylTap
Audiophile

Posts: 1123
Location: USA - SouthEast
Joined: November 16, 2007
 ... while I like your amps quite a bit, you lose a lot of credibility with me when you call Jolida and Cayin "junk" and in the next breath start talking about how great the amps are that you make a living on without disclosing such...

Don't misunderstand me, the amps you mention are all fine amps and are a step above Jolida and Cayin in price and performance, but to call them "junk" is just irresponsible.


"I'll play it and tell you what it is later..." - Miles Davis
How about a Dynaco MKIII upgrade or kit, posted on November 5, 2009 at 14:45:08
Frihed89
Audiophile

Posts: 8435
Location: Copenhagen
Joined: March 21, 2005
 It will cost a lot less than the amps you name and sound a lot better, too. Or how about a Quad II 40? That will cost more. The 275 probably sounds the best.
"What did the Romans ever do for us?"
RE: Driving Kt-88, posted on November 5, 2009 at 06:44:52
dynacopas
Audiophile

Posts: 45
Location: Central AL
Joined: September 26, 2009
 Well the 12ax7 has tons of gain. And my understanding is unless the circuit requires alot of gain they go with the 6sn7. Now my allen organ model 75's run through the 6sn7 and then back through the other side of the 6sn7 to ramp up the signal getting more gain. There are arguments that the 6sn7 is also more musical. But that has been debated for years and will continue to be. A 12ax7 is actually (2) 6au6 tubes if I understand it right. Basically it all comes down to the circuit and the designers preference.
Allen 75's,Eico HF60's Dyanco PAS3x, Orcale Delphi Mark 2, RCA MI-9358A, MI-9257C
Not sure why this would be a buying criteria...., posted on November 5, 2009 at 05:31:41
doodlebug
Audiophile

Posts: 1740
Location: Little Rock, Arkansas
Joined: July 27, 2006
 There are plenty of excellent circuit designs using KT-88s or variants. For instance, The HK Citation II uses 12BY7 (intended as a wide-band video amp tube), the McIntosh MC-275s use the 12BH7, (similar to the 12BY7).

I'd suggest this implies that the choice of tube compliment isn't necessarily the criteria. It is the circuit architecture/topology and how the designer implements it. The good news is that many of the basic topologies are well known and discussed for decades.

Cheers,

David

RE: Driving Kt-88, posted on November 5, 2009 at 05:01:26
danlaudionut
Audiophile

Posts: 3564
Location: Upstate NY
Joined: June 6, 2002
 The octals (6sn7 & 6SL7) are much more
linear than their 9 pin cousins.
If you are using alot of feedback
that probably doesn't matter.

From highest rp and mu to lowest rp and mu
12AX7
12AT7 & 6SL7
12AV7
12AU7 & 6SN7
12AX7 has 5 times the gain and
10 times the rp of the 6SN7.

Jolida uses 12AX7s for the first stage
and 12AT7 for the driver stage.
Many designs use a 6SL7 for the first stage
and the 6SN7 for the driver stage.

DanL
RE: Driving Kt-88, posted on November 5, 2009 at 06:37:53
MillHouse1835@aol.com
Audiophile

Posts: 197
Location: South Carolina
Joined: March 19, 2007
 thanks. I have heard people say that the 6SN7 was more "musical", which is subjective (?) and that the 12ax7 was developed to be simply smaller (?).
All some of the comments I have seen posted. It does seem that 12ax7 based amps have more wattage than 6sn7 amps from the same pair/channel of KT88's. I'm not a designer or tech. Just interested in hearing comments. thanks again

RE: Driving Kt-88, posted on November 5, 2009 at 09:53:28
danlaudionut
Audiophile

Posts: 3564
Location: Upstate NY
Joined: June 6, 2002
 The 6SN7 IS more accurate than any 12A*7 tube.
6SN7 has the gain of 20
12AX7 has the gain of 100
Completely different animals.

Wattage depends on a couple of things ....
Class AB has more power than a Class A/AB
Class A/AB has more power than a Class A
Pentode has more power than UltraLinear
UltraLinear has more power than Triode
The more power the less accurate and therefore
the more feedback you need to get the accuracy back.
Personally I don't like feedback.
I have taken heat for it but I know what I like.

A Class A PP Triode EL34 amp will give you 10-15 watts.
A Class AB PP UL EL34 amp will give you 20-35 watts.
A Class AB PP Pentode EL34 will give you 50+ watts.

DanL
RE: Driving Kt-88, posted on November 5, 2009 at 07:16:58
geraldm121
Audiophile

Posts: 159
Location: connecticut
Joined: January 9, 2007
 Cayin actually makes two different integrated amps with similar specs that use both types of tubes in the front end. The A88T uses the 6 series octals and the A70T uses the 12 series 9 pin miniatures.Personally I went for the A70 based on my own tube stash inventory and the "semi" tube rectification.

RE: Driving Kt-88, posted on November 5, 2009 at 07:06:20
Mendel
Audiophile

Posts: 16
Location: GTA
Joined: January 17, 2009
 The Rogue Audio Stereo 90 gets 90 watts per channel with a pair of KT88 per side.It uses 12ax7 for input tubes and 6sn7 for drivers, so you get the best of both worlds! They can also take KT88, 6550,EL34,KT77,KT66,6L6GC etc for output tubes. Makes for a lot of tube rolling possibilities. Also switchable to triode for 45 watts/channel. Good solid amps that sound like whatever tubes you put into them.

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