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In the process of selecting a higher powered tube amplifier I came across this Bob Carver interview regarding ultra-linear. I'm assuming that with their popularity and continued production that the issues mentioned in this article have been worked around by now.
["I met Stu Hegeman when he went to CES to show his new Happi One preamp. He told me that ultra linear was the worst fad of all time, that he only designed one that way, that it was the biggest blunder of his career, and he would never design an ultra linear output stage ever again. And he didn't. He designed lots of amps for Sidney Harman and for Lafayette, and only one was designed to be ultra-linear, the Citation II. Sidney, his boss, made him run the KT88s at 0.100 amps per tube with 500 (earlier) volts on the plate at idle (see Sam's photofact). 50 watts for a tube rated at 35 watts! Sidney wanted to have low distortion to compete with Marantz. Stu objected, but Sidney made him. He relented after too many tubes blew up, frying the screen resistors and the Citation division of Harman Kardon had to fix them all."
"The other problem with ultra-linear is that the screen grid is pushed too low when the plate pulls close to ground at high output. This limits the maximum output current to a rather wimpy value and makes the amplifier's power response very peaky, falling off rapidly as we go away from the ideal loading. Speakers do that. Stu taught me all this one enchanting day at CES. Before that I believed everything I read about ultralinear as being the cat's meow and the hot set-up. Then I noticed that the tube amps I loved the most were pure pentode, not ultra-linear (Citation V, Lafayette 550, Mesa Baron, I could go on and on). My heroes are Einstein, Gandhi, Hegeman. Hegeman got it right. So much for Ultra Linear!"]
Follow Ups:
My new amplifier has two switches - UL and Triode as well as Max feedback and min feedback. The rational from the manufacturer who makes several speakers felt that for certain music and speakers the UL option is desirable for some while Triode is desirable for others. Personally so far I prefer the Triode operation with min feedback but I can see the appeal of the UL with max feedback. Quite a difference.
The UL mode offers about double the power so depending on the speakers that could be a factor as the company makes their own LS-3/5a at 82db sensitive.
Still it's nice to have options to tailor the sound less intrusively than bass/treble
Interesting product. What's involved when your Audio Space gear needs service?
There are dealers in the U.S. and Canada. Like any other product you send it back to the dealer - they fix it and return it. They've been around a long time so it's not a fly-by-night.
Finding the US distributor page is somewhat confusing as the distributor is called Gini systems
Well, no that's not, "Like any other product" I own. I don't have an issue sending something abroad to a manufacture for repair of upgrade. Dealer repair? No thanks.
Sorry.
I get the sense that most people are bit old school like me and when something breaks I like to go back to the store I bought it from and have them repair it or send it away for me.
The dealer is located in HK - I went to their shop which is a dedicated Audio Space showroom (they have a new bigger one) and I met the co-owner. I wanted to hear the speakers before I accepted them for review. Simply because it wastes my time to listen to something for a month so I prefer to hear them first.
For me personally it helps that the dealer is also the co-owner designer. They can do repairs and upgrades on-site. Numerous cap upgrades and piles of tubes for sale. I think I have a picture of the place in my camera so when I post my third installment on dagogo's commenary section I will include one of their showroom.
You are quite right - it's a global world so it doesn't really matter where the store is locted. It would be the same for bigger brands as well - When my HP computer died I had to ship it to HP.
Good LS3/5As will work fine with 12W in your triode mode. Mine are driven both by a 12W PP triode amp and my 9-10W Meishu. Even Peter Qvortrup believes the LS3/5As sound good on his gear!
Observe, before you think
I have just finished my review of the Audio Space LS-3/5a and their dedicated subs make all the difference in the world - great combo. I'm sitting here waiting for them to pick up the speakers.
I am back to listening to the AX Two which doesn't give up much in the bass amazingly enough(yes against the sub - and makes me think even more highly of them). I wonder if Peter would consider making subwoofers like that. The LS-3/5a subs integrate about as well as I have ever heard any sub integrate. I know Peter hates subs but he did like down-firing designs in the Snell Type A. I don't see why they could not do that for any standmount - design it strictly for the model.
I can't really compare LS-3/5a models since *ahem* the speakers came out when I was something like 3 years old. The AX Twos in corners free up more space ultimately being able to stick them in corners - still need to fill the stands and possibly get bass traps. I wasn't expecting the level of bass out of the AX Two because most standmounts in this price range are laughably anaemic. The trouble is finding something to fill the stands.
There is no home depot or Wal-mart where everything is under one roof. You have to go to certain marketing districts to find anything - but of course you need to know "where" product A is. You'd think the hi-fi stores would sell this right? Nope. The place that sells acoustic foam doesn't sell any methiod of attaching it to the walls. So I sit for a month with acoustic foam all over my apartment trying various glues that either don't work or eat a hole through the foam. Finally found two way tape that works but I bet it rips the paint of the wall when it comes down. Arggh.
The Audio Space amp has no trouble with the combo at all - the UL switch seemed to merely compress the sound (on the LS-3/5a) a little - bringing everything to a flat plane (hence the SS sound) and loses the third dimension and depth. Though still sounds good just not as good as the triode mode. The headphone amp section was worth the price by itself which was ultimately why I bought it. My ASL MG Head and Total Bithead amps will go up for sale. The fact that you can operate it as just a power amp and the terrific build quality don't hurt none.
I'm listening to Techno music Tiesto club life Miami Vol 2 and Audio Note always amazes me that even their AX Two can play this with in the chest bass at pretty high levels.
I would love the Meishu - that was the first amp I heard that turned the entire audio hobby on end for me. That amp combo with E destroyed the first 15 years of audio listening and embarrassed EVERY system by everyone over those 15 years. Interestingly I always think back and wonder if I should take a more serious look at the Meishu. Especially here in HK where apartments are smaller and it would not need to fill the big western living spaces - here the entire apartment range from 432 to 1000 square feet. No wonder the Line Magnetic dealer said their 3 watt EL 84 based SET could drive the ATC 150s. The Meishu would be a behemoth.
I don't think that destroying the current limiting resistor for the screen grid is much of a problem, but other than that Hegeman made some interesting and valid points. Basically the "ultra-linear" configuration adds taps to the primary winding to apply feedback to the screen grids. This is just of one of many ways to do something similar.
Audio Research has always used a configuration that ties the cathodes to the secondary winding to provide feedback around the transformer. McIntosh had multiple windings to transfer some of the load directly to the cathodes. Others use no feedback around the output stage whatsoever (pretty much confined to low-powered triode designs).
Clearly there is no single "best" solution, or everyone would use it. There are always trade-offs involved in any product design, even with something as simple as toasters. Often the trade-off is that a better solution costs more. The "ultra-linear" output stage invented by Hafler and Keroes in the early '50s (or maybe by Blumlein before that -- it usually turns out that he was actually the first to have invented many audio designs, but for some reason didn't receive credit for many of them).
As usual, the best thing to do is listen. If you like the sound and it fits in your budget, that is the real "best" design.
UL comes to us from a patent in the 1950s. The original patent called for a very specific point on the transformer for the screen tap. If done that way you got the linearity of a triode with about 90% of the pentode power.
Other companies wanted this but did not pay the original patent holder, and got around the patent by changing the point of the tap. This had consequences, not the least of which was the triode linearity suffered.
The point of this is not all UL are the same. Do they use the correct tap point? For example, Dynaco never did.
What Stu says is true (the reliability issue had nothing to do with it being UL, BTW), but it makes a difference how hard you push the amp. If you don't drive it hard the load sensitivity does not manifest. However tube power is expensive so as audiophiles we tend to buy amps that have 'enough' power and then try to use every drop.
Its for this reason I have always preferred triodes. True, they are more expensive but due to the distortion characteristics they have a greater amount of 'usable' power. IOW you can push them harder before they get unpleasant.
Assuming that the 50's UL patent has expired, are there any manufactures that use the correct tap?
Speaking generally and or subjectively, if triode is preferred which would come next pentode or UL?
You would have to inquire with the manufacturer.
I suspect the answer to the latter is very design/execution dependent, and also depends on the speaker. In your case, the speaker has a linear impedance curve, this would be better for UL.
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