I often wondered why the term "ultra-linear" came to be. Did it refer to curve B in the diagram? If so that has little to do with the stage's performance in terms of low distortion. It is not the linearity of the Va/Ia characteristic that counts, but the linearity of the Vg1/Va graph, or then the Vg1/Ia. This is shown by equal distances between different Vg1 curves where they cross the plate load line, for equal Vg1 differences.
The advantage of the UL or distributed load option simply lies in that the best of the triode world can be obtained together with the best of the pentode world for optimal g2 taps. One must also be careful not to regard g2 simply as another input grid. It draws current and therefore has a specific 'input impedance' (something like rp) in contrast to the g1 infinite input impedance at audio freuqency. For this reason there is a measurable difference beteen using power pentodes (EL34) or beam tubes (KT66, 6L6GC) in UL, other things being equal. The greater variation in g2 current drawn by beam tubes depending on the output given, causes a large variation in 'input' impedance when used in the UL mode.
These were some notes I took . I forgot to tie them with a circuit alas , it would take time to find it . Had I known I would show them I would have taken more care . This was one rare time I got 16.5 db feedback to work as I wanted . A bunch of transistors helping . These were rejected as my friend who I built the amp for wouldn't want that . What to my eyes is most interesting is how mediocre the fake triode is , this is usually chosen without a second thought . Also how OK pentode is . For various reasons pentode is not optimum as it was not being sort as a possibility ( 3 K g2 to HT of 450 V ) . The transformer by chance offered spare taps which serve OK for unconventional UL . I think it is interesting enough to make it worth showing . If feedback is removed it is a different story .
It is simple to say UL offers an optimum . There is a little bit more to it than that . I never found it's exact equivalent by using various other types of feedback . The so called cathode UL feedback seemed to be different if looking at the spectra . I had 17 V rms to feed into the cathode sitting at 39 V at clipping when looking at that version . Doubtless not optimum ?
As I have liked EL 34 the most of the valves I have , I must try g3 at 0V as EL 34 will allow that .
One thing people overlook is the pentode's ability to work with a slightly less good power supply . This coupled with some feedback might give good distortion and low hum .
One thing my test proved is that a centre tapped AC PSU to the heaters is very close to DC . Sometimes no measured difference at all .
Another reason to look at UL again is that SE amps might suit it better . This is well documented in UL design notes although not specifically about SE ( cross coupling in PP and ringing ) .
Damping factors . 3 is OK , 16 is plenty .
When using loop feedback on my SE amp up to 9.5 dB the trends seem the same as no feedback albeit lower distortion . Above that not so nice .
Of the feedback I tried other than UL and liked was simple capacitor coupled shunt feedback to g1 . It looks very much like fake triode ( g2 to plate ) . One can add that instead of loop feedback . A bit of both might be excellent ?
This is a nice write up on UL shortly after first commercial use . Note Blumlein had thought of it when the first beam Tetrodes had appeared about 20 years before .
Tetrodes with Screen Feedback
BTW my graphs previously were for an Alex Kitic type amp with plate feedback removed and made loop . I abandoned it as I felt distortion levels were too high . I manged without any obvious feedback to equal these ( loop ) .
Tetrodes with Screen Feedback
BTW my graphs previously were for an Alex Kitic type amp with plate feedback removed and made loop . I abandoned it as I felt distortion levels were too high . I manged without any obvious feedback to equal these ( loop ) .
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Because it is more linear than both pentode and triode mode.
http://www.diyaudio.com/forums/tube...en-ultralinear-triode-mode-2.html#post3279143
That is why it is wrong to say that Blumlein invented UL. He didn't. Blumlein invented distributed loading, but it was Hafler and Keroes who discovered it would become UL under the right conditions.
I mistakenly lumped Gu 50 with Beam tetrodes earlier . The mistake was taking the name Ray Pentode I have seen associated with them to mean more than it did . There are hybrids out there , Rod pentodes which are as far as I can see a very different animal . I mistakenly took Gu 50 to share some similarities .
Russian Rod Pentodes | Radios-tv.co.uk
I read this some time ago . Strapping G3 to anode produces big wobbles in the curves .
http://www.kaponk.com/~yanyong/ETF06TS.pdf
I hope others will add to this as pentodes are very interesting devices . I was looking today to see how much current I could take from g2 of EL 34 . I suspect 10 mA ? If I was to take 10 + 10 mA at 800 V what might I get ? The idea being to put a resistance in the anode to force it to happen . EL 34's are cheap enough to risk . Would I get a better triode ? 800 V is 16 watts dissipation . The idea is to offset the grids to cancel . Then look at the mix of current after that . Joy of joys if the anode can be increased to full dissipation and get a better curve .
If looking at my so called pentode curves of EL 34 there is a hint of this ( No 63 ) . A typical pentode amplifier would seek higher gain . The gain advantage of full pentode mode from Mullard data is 8.7 V rms g1 = 11 W 18.9 Vrms g1 = 6 W triode . If my maths is right a gain advantage of about 3 or 9.5 dB . If one is very careful a full 11 watts from one valve with lower hum and comparable distortion albeit of different spectrum . The PYE Mozart gave 10 watts at 0.3% distortion . It truly was a hi fi amp using one EL 34 if to DIN 45500 .
http://www.doramusic.com/patents/496883.htm
Russian Rod Pentodes | Radios-tv.co.uk
I read this some time ago . Strapping G3 to anode produces big wobbles in the curves .
http://www.kaponk.com/~yanyong/ETF06TS.pdf
I hope others will add to this as pentodes are very interesting devices . I was looking today to see how much current I could take from g2 of EL 34 . I suspect 10 mA ? If I was to take 10 + 10 mA at 800 V what might I get ? The idea being to put a resistance in the anode to force it to happen . EL 34's are cheap enough to risk . Would I get a better triode ? 800 V is 16 watts dissipation . The idea is to offset the grids to cancel . Then look at the mix of current after that . Joy of joys if the anode can be increased to full dissipation and get a better curve .
If looking at my so called pentode curves of EL 34 there is a hint of this ( No 63 ) . A typical pentode amplifier would seek higher gain . The gain advantage of full pentode mode from Mullard data is 8.7 V rms g1 = 11 W 18.9 Vrms g1 = 6 W triode . If my maths is right a gain advantage of about 3 or 9.5 dB . If one is very careful a full 11 watts from one valve with lower hum and comparable distortion albeit of different spectrum . The PYE Mozart gave 10 watts at 0.3% distortion . It truly was a hi fi amp using one EL 34 if to DIN 45500 .
http://www.doramusic.com/patents/496883.htm
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I hope the gentleman who asked why we used input stage pentode is satisfied with the various answers ? Forgive me for including all pentodes . If driving a 845 triode I guess an EL 34 can be an input device ?
Alan Blumlein was lent to Mr Churchill by his boss Mr Schoenberg . Alan died testing a type of radar which if I am correct was said by Goering to have shortened the war by 2 years . His family wasn't told how he died . His genius makes me think UL distributed load was obvious to him even if he didn't get involved with naming of it . I think this is the house ( so much like my own , recent additions no doubt ) ? I hope it gets a blue plaque one day ( our famous people get them , Mr Handle and Jimmy Hendrix neighbours in Soho do )
Alan Blumlein was lent to Mr Churchill by his boss Mr Schoenberg . Alan died testing a type of radar which if I am correct was said by Goering to have shortened the war by 2 years . His family wasn't told how he died . His genius makes me think UL distributed load was obvious to him even if he didn't get involved with naming of it . I think this is the house ( so much like my own , recent additions no doubt ) ? I hope it gets a blue plaque one day ( our famous people get them , Mr Handle and Jimmy Hendrix neighbours in Soho do )
triode wired, the EL34 was used as driver tubes for high powered triode pp amps like the MY3-275....http://tubedata.tubes.se/sheets/129/m/MY3-275.pdf
Glad to say there is a plaque .
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I think PCL 84 drives 211 well ? My experiments seem to favour a pentode over a triode on all count if driving a triode . My next step is to have a UL driver transformer , cost is about $50 . Loosely speaking still why use an input pentode . MY3-275 , wow !!
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I think PCL 84 drives 211 well ? My experiments seem to favour a pentode over a triode on all count if driving a triode . My next step is to have a UL driver transformer , cost is about $50 . Loosely speaking still why use an input pentode . MY3-275 , wow !!
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I am if no one has guessed dyslexic . Alan Blumlein so badly so he would have failed to advance at school . His mother paid a man who usually got people into university to get her son to read and write . It was this man who first identified his talent .
I employed a man called Bob who appeared in the film The Leather Boys on his BSA Gold Star . Many years later he asked me how he passed his interview . Simple I said , you told me you maintained that Gold Star . Bob could co anything I asked . Often things beyond the possible if reading a book about it ( bearings ) . To top that he could do it with tools barely able to do it . It was years later I found out that he had the writing age of an 8 year old . Later he told me that he had wired most of the flight decks of the Concorde's . He had a friend do all the paper work ! He told me the French twigged it and didn't care . The Brits never did . Not a boastful man , took him about 9 years to say it .
Like the various people in history I never met Alan Blumlein except in his ideas . The story I liked is if he found a young engineer struggling with a problem he would say he was bit bored and might he help ! I wish he would in spirit form do that for me .
Sorry we got so far away from why input pentodes were popular . For what it is worth I guess transistors did it better ? Very rare one saw a hybrid so even that theory holds no water .
I employed a man called Bob who appeared in the film The Leather Boys on his BSA Gold Star . Many years later he asked me how he passed his interview . Simple I said , you told me you maintained that Gold Star . Bob could co anything I asked . Often things beyond the possible if reading a book about it ( bearings ) . To top that he could do it with tools barely able to do it . It was years later I found out that he had the writing age of an 8 year old . Later he told me that he had wired most of the flight decks of the Concorde's . He had a friend do all the paper work ! He told me the French twigged it and didn't care . The Brits never did . Not a boastful man , took him about 9 years to say it .
Like the various people in history I never met Alan Blumlein except in his ideas . The story I liked is if he found a young engineer struggling with a problem he would say he was bit bored and might he help ! I wish he would in spirit form do that for me .
Sorry we got so far away from why input pentodes were popular . For what it is worth I guess transistors did it better ? Very rare one saw a hybrid so even that theory holds no water .
With the 6M11, one thing you could do is use the two triodes as an LTP splitter, with the pent in service as an active tail load. That just might save you an extra hole in the chassis if you didn't want to solid state the tail load.
Let's not forget color TV vid amps. That's what the 12BY7A was originally designed to do.
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Apart from EL 84, 34 Gu 50 what plentiful pentodes are worth looking at ?
I suspect some have the beating of 300B and 211 if triode strapped ? Price would be important as would the tube base . Gu 50 is not a standard type which is a pain . Ones that resemble a big EL 34 would be good . $50 is about as high as I want to go . In current production would be even better .
In transistors the video type devices are well liked . MPSA 42/92 are similar survivors . BF720/721 resemble video devices .
I suspect some have the beating of 300B and 211 if triode strapped ? Price would be important as would the tube base . Gu 50 is not a standard type which is a pain . Ones that resemble a big EL 34 would be good . $50 is about as high as I want to go . In current production would be even better .
In transistors the video type devices are well liked . MPSA 42/92 are similar survivors . BF720/721 resemble video devices .
I like TV horizontal and vertical deflection types: 6BQ6GA/GTB, 6CB5, 6AV5, 6DQ5, 6LW6 (horizontal deflection types -- some of these are real beasts that can put out north of 100W at reasonable rail voltages).
Some vertical deflection types: 6LR8 (small signal triode + beam former) this one can use the triodes as either an LTP driver or cathode follower grid drivers) The 10JA5 also looks good. These vertical deflection types can also use stock OPTs, as their loads come close to what's available "off the shelf", and the distortion performance looks pretty good if you don't need more than ~30W.
As for availability, it's pretty good if you go for the odd heater voltages as lots of these were made in many different heater voltages to accommodate series heater strings across the AC mains in TV sets that didn't use a PTX.
Some of these will work as pseudotriodes, and can tolerate considerable V22 spec busting if used in this manner (6AV5s in particular). Others, not so much and/or it's brand specific. YMMV if you try it.
The main problem with these, and probably the spec sheets make no mention of audio final use for this reason, is that they don't work so good as Class A amps, as the most linear part of the characteristic is well within red plate territory. As Class A, SE amps, they do sound good until the glass melts. Otherwise, you have to use 'em as Class AB, PP finals to hit the most linear part of the characteristic.
In that regard, the high current capability makes for easier to design and build OPTs since the Rl / phase is so much lower. (4K4 (P-2-P) works just fine with 6BQ6s, and that, too, comes close to a stock OPT that was intended for Class A, PP 6L6s -- though you do sacrifice some power output capability if you use such an OPT -- which I did as I already had one in the junk box.)
Thanks for that . I wish my late brother was around to join in .
Sort of on my list although a museum device .
813 @ The National Valve Museum
Sort of on my list although a museum device .
813 @ The National Valve Museum
^^
No worse than the tolerances for most other types. (The only type that's notorious for this that I heard of is the 6SJ7, but that's a small signal pent.) I found that in circuit performance comes to within 5% of design nominal predictions, and that the H3 predictions from loadlines are "high side" errors. First I ever heard of this claim.
No worse than the tolerances for most other types. (The only type that's notorious for this that I heard of is the 6SJ7, but that's a small signal pent.) I found that in circuit performance comes to within 5% of design nominal predictions, and that the H3 predictions from loadlines are "high side" errors. First I ever heard of this claim.
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