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In Reply to: Why do some people dislike UL? posted by Ray Moth on March 17, 2007 at 14:12:56:
If UL is SO bad why were the most popular tube amps, dynacos all UL among many other amps?
Then again a triode PP amp has lower power than an UL or pentode but is more linear(more accurate)
Follow Ups:
To realize full advantages of pentode connection, special stable power supply is needed for G2. UL comes at no extra cost, just taps in the transformer's primary.As it is common in industry, cost-saving solution was advertized as something that improves quality. Hence this meaningless term "ultralinear".
I think there is a flaw in your logic.A screen supply for a pentode can be as cheap as a couple pieces of wire and an r-c (with a small capacitor) section. If the maker was looking for the cheapest way out, then they certainly wouldn't invest in a sophisticated (read:expensive) screen supply. They would use a cheapie supply.
The taps off the OPT are not free - they don't cost a lot, but they do cost something.
So the cost difference between the two approaches can be negligible if the maker so desires.
And if U/L is just cheaper and offers no advantages, why do you think Stu Hegeman used it in the Cit II?
The real question is whether UL should be recommended for DIY, and from most of the posts here it should not. Sure, with a lot of professional engineering, talent, time, and equipment, almost everything can be made to sound good. Even transistors. But average DIY Joe is not Stu Hegeman, he needs something simple that works without much tweaking and he does not need circuit antics a la Citation II or Macintosh. Would you recommend someone to make a DIY Cit II?As to feeding g2 from B+ through series resistor, this is the worst way to do pentode connection. It only works with Ug2 close to Ua, and has poor regulation. Which of these two evils is worse, UL or series resistor g2, is not worthy of discussion.
"The real question is whether UL should be recommended for DIY,"The question I responded to was related to cost, and if that (cost) was the reason U/L output stages were used. So this is a different question.
Why not use it for DIY? With all the other gyrations DIY builders go through, why shouldn't optimizing a U/L stage be an acceptable endeavor? There are any number of complex and challenging issues that DIYers dive into routinely (power supply anyone?), why should this be any different?
"Would you recommend someone to make a DIY Cit II?"
Sure!! In a heartbeat. Why not? The key is that to do it will require OPTs of the highest quality - which aren't cheap. Of course, neither are the Teflon caps and silver wire that DIYers often use.
"As to feeding g2 from B+ through series resistor, this is the worst way to do pentode connection."
I didn't say it was any good, I said it was cheap. And the purpose of mentioning it was to demonstrate how the cost difference between U/L and pure pentode could be reduced to insignificant levels. I will also say that some damn fine sounding gear feeds the screens just that way. Could you improve it? Of course! But that doesn't mean it can't sound very good despite it being cheap.
I'm not a crusader/"true believer" in U/L or any given topology. I used the Cit II to illustrate a point. That point is that you can make a great sounding amp with a U/L stage - as you can with pentode, triode, or any other stage as long as it's well executed.
You certainly can have a personal preference or favorite, but just because you or I like something the best doesn't mean it is the best. Is chocolate better than vanilla because I like chocolate better??
But when building the a DIY Deuce, do it monoblock. Consider also lowering B+ to allow lower plate dissipation valves, or to go closer to Class A.866's for the rectifiers would be a nice touch while you're at it.
> And if U/L is just cheaper and offers no advantages, why do you think Stu Hegeman used it in the Cit II?Not all new topologies are implemented for sonic superiority. The popularity of UL had as much to do with marketing as anything else.
So you are saying what here? It can't work well? The Cit II is no good?Look at the marketing material of the day (you can see a 1961 brochure on my site if you want). There was no mention of UL or "distributed load" except in the spec sheet where it describes the output section in just a few words.
I'm confident the choice was made for performance reasons. There is virtually nothing about a Cit II that followed the trends of the day, there's no reason to believe the UL output was an exception to that.
> I'm confident the choice was made for performance reasons.Which of HK's product specifications improved as a result of applying the UL technique? If the answer is "none," and if you're correct that this wasn't market-driven, then perhaps it was just an excercise in innovation. Engineers do that sometimes.
"Which of HK's product specifications improved as a result of applying the UL technique?"Improved as compared to what? If there was EVER a "clean sheet of paper" design the II was one of them. And H-K wasn't U/L across the board. The Cit V was a true pentode amp (and it's marvelous!).
"If the answer is "none," and if you're correct that this wasn't market-driven, then perhaps it was just an excercise in innovation. Engineers do that sometimes."
Sure, that happens in a lot of fields.
But in addition to the published material, I've had the honor of speaking with people who were personally well acquainted with Stu before he passed away. They tell me to a man that he was absolutely driven to make the finest amplifier in the world. He could have chosen triode, pentode, U/L, whatever. He had free reign. He chose U/L. And really, by 1959-1960 U/L was hardly an innovation, it had been around for 5-6 years.
There was only one design and one construction compromise in the Cit II that Stu made anyone aware of - and it wasn't the ouput stage.
1. Construction - It had to be buildable by an average Joe - the huge majority of those amps were kits.
2. Design - Stu was not able to resolve a 1 Hz oscillation in the Cit II the way he wanted. He ended up using a different approach to solving the problem than he wanted because he ran out of time to work on it. The amp was scheduled to begin production, and he simply had to use a less elegant solution than he preferred.
With the benefit of way more time and much better parts than he had, I've been able to eliminate the 1Hz oscillation without applying Stu's fix. I must tell you, his fix may not have been as elegant as he wanted, but it is totally inaudible - and fixes the problem.
In light of all this, do you still believe he used U/L just as a marketing gimmick, or just to prove he could??
> In light of all this, do you still believe he used U/L just as a marketing gimmick, or just to prove he could??Please don't misquote me for your own purpose. You said earlier that you are confident the choice was made for performance reasons. To that, I asked which of HK's product specifications improved as a result of applying the UL technique? I was of course referring to HK's previous/parallel, non-UL power amplifier products and circuitry. If you have no definitive answer to this question, then I think it might be difficult to demonstrate that the basis for designing a UL output stage was performance-motivated.
One last issue here. You wrote in two earlier posts:"The popularity of UL had as much to do with marketing as anything else."
And later:
"If the answer is "none," and if you're correct that this wasn't market-driven, then perhaps it was just an excercise in innovation."
In my reply I wrote that "In light of all this, do you still believe he used U/L just as a marketing gimmick, or just to prove he could??"
That was not a quote, I was paraphrasing what you said. In light of your actual quotes above, do you think I paraphrased inaccurately or inappropriately? I apologize if I did, but I really don't think that's the case. Other viewers of this post can decide for themselves I guess.
You weren't misquoted - your actual quotes are in my post so there is no possible way to misquote you. No way."You said earlier that you are confident the choice was made for performance reasons."
Yes, and that was based on a number of different things as I said.
"To that, I asked which of HK's product specifications improved as a result of applying the UL technique? I was of course referring to HK's previous/parallel, non-UL power amplifier products and circuitry."
There was VERY little in the Cit II that was common to any earlier H-K stuff. No other H-K product up to that time had used that tube set, those OPTs, the multiple loop NFB, the low impedance power supply, and so on. What is it about "clean sheet of paper" that you don't understand? Do you really want to compare the Cit II to an A-300?? It's ludicrous.
If the change to U/L was the only change (or the only significant change) then your narrow-focused question could be answered. But there really is no H-K product to draw a direct comparison to!!
It doesn't mean anything, but since you seem intent on having some sort of answer (relevant or not), here is a quick list.
Compared to prior H-K designs, the Cit II...
1. Had octaves wider bandwidth
1a. Had an OPT resonant frequency in the 450K area! This made a lot of other things possible in the design.
2. Had much higher RMS and peak power
3. Had lower THD at a given power output
4. Had lower hum and noise
5. Had a higher damping factor
6. Used much higher total NFB. Used lower loop NFB.
Properly implemented UL will show better open loop performance than pentode as regards bass distortion and load tolerance, with a relatively small penalty in efficiency. Compared with triode, it will have less Millering (hence better OL bandwidth and a better spreading of the poles making feedback more stable) and markedly better efficiency. Some of these things will show up on the spec sheet (power), some won't (LF distortion, load tolerance) but will be audible. Your Procrustean restriction to the spec sheet alone is curious and telling- do you really think that all design virtues are contained therein?The two key words are "properly implemented." Slap a cheap piece of shit transformer in and you'll have grief; the best topology for shitty transformers is probably Circlotron.
disclaimer: My own design choices do not include ultralinear. But in the past I've built UL amps with excellent performance, so it's not beyond the capabilities of a DIYer.
> Properly implemented UL will show better open loop performance than pentode as regards bass distortion and load tolerance
Ahh, semantics. Very good.
they hapeened to have a U/L tap? ;-)
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