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In Reply to: Re: Because in my own extensive tests, it lost information... posted by Eli Duttman on March 18, 2007 at 05:36:29:
Hi."TANSTAAFL" is short of There Aain't No Such Thing As A Free Lunch".
Mind you, take care to use it as it is the official name of wire supplies company in USA, specialized in HV (25KV) & HT (538C) wires.
Agreed to your comment on UL needs high qualtiy O/P iron which are "expensive" to buy.
Here is what Norman H. Crowhurst said his his publshed paper in Nov 1959:
"In the case of Ultra-Linear the choice of the tube operation is vertually one btween pentode & triode. The tappings on the transformer primary "split the difference" between connecting the screen to B+ or directly to plates. The first is pentode, the second is triode. Connecting them to a tapping results in Ultra-Linear. The achieves practically the efficiency of a pentrode while maintain the linearity or lower-order distortion of a triode.
This would seem to be ideal. The difficulty is that, to work perfectly, the transformer must maintain the correct tapping, both in voltage & phase, of ALL audio frequencies. This is not too difficult for the low frequency end but, at the high frequency end, stray leakage inductances between different parts of the winding, along with the winding intercapacitances, can really play HAVOC
with an U-L circuit resulting in some quite weird waveforms at some specific frequencies."The solution as Norman suggested is to get a "correctly designed" U-L transformer to "avoid any spurious deviation from correct tapping up to a frequency beyond the audio range and ALSO beyond the cutoff of the transformer".
This not impossible, but only relatively few irons so built under the name of U-L achieve this objective.
Frankly, I modified my ST-70 with switchable UL/triode strapped, I always listen with the power tubes triode strapped since day one as I am not that impressed by its original U-L mode.
c-J
Follow Ups:
Thanks, c-J, that is just the sort of comment I've read from a number of people who have tried UL and didn't like it. I believe the ST-70 was designed by one of the founders of UL, if not actually its inventor, so one would think that his UL product should be as good as it gets. (I know the ST-70 front end was mediocre but, hey, we can't all be good at everything!)Yet if, as you say, the ST-70 sounds better in triode mode, then why did he use UL? Could it have been a matter of pride in his own topology, or lack of appreciation of good sound, or commercial pressure to provide more power than triode mode could give?
Hi.& was later popularized by David Haflter & Herbert Keroes in early 1950s.
I thought he designed guns for Wyatt Earp? - just kidding ;)Yes, I know what you're saying, that was why I tried to choose my words carefully. However, the fact remains that nothing much came of the idea until, as you say, H & K came along, found out more about it, calle it "Ultralinear" and popularized it.
The question still remains in my mind: Why did Hafler, of all people, design and build a UL amp that sounds significantly better in triode mode? (I'm not speakinmg from personal experience; I've never even seen a Dynaco amp, but you're not the only person who has reported a similar finding.)
Hi.I don't know why this shared O/P load topology was so called "Ultra-linear". Technically, it is sorta kinda a blend-up of a pentode efficieny & a triode low-distortion transfer.
If you compare a U-L transfer chart, you will see the transfer traces look like a very distored triode transfer curve, kinked in a way towards a pentode curve. The curve forms of course change per the tapping percentage on the primary of the O/P iron.
Although commonly it was 43%, but Mullard used 20% & LEAK used 50%.
Both Peter Walker of QUAD, & Williamson objected using the term
"ultra-linear" & preferred the more appropriate terminology of "distrributed load", to which I concur.Put asisde the O/P power efficiency being much better than a trioide, which IMO, is the objective of U-L design, its transfer curve clearly told us it can't outperform a triode's linearity.
So why called it "ultra linear"? I scratched my head on this terminology. IMO, it could be a marketing tactics, who knows?
c-J
Hi ,
Mullard used 20% taps for higher output power or 43% for minimum distortion . Leak designs used 43% screen taps , they also used series resistors between the screen and screen taps in an attempt to reduce distortion . Williamson never advocated ultra linear in the original 1947 article or the later 1949 addendum published in Wireless World . Later designs which were based on the Williamson input stage and driver did . Quad 2 topology is somewhat different to UL , the load is split 90% to the anode and 10% to the cathode , no screen taps at all , this supposedly provides a low output impedence with pentodes with far greater power efficiency than triodescheers
c-J, where did you find it? Please share it!
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