Hi Douglas,
No, not all wisdom - but at least some in a time when there often was even less from elsewhere. And his design graphs were all quite useful; couldn't get along without them.
I try not to judge a guy by his worst or last game, but by his best. Had far too much of that myself. But point taken.
Regards.
No, not all wisdom - but at least some in a time when there often was even less from elsewhere. And his design graphs were all quite useful; couldn't get along without them.
I try not to judge a guy by his worst or last game, but by his best. Had far too much of that myself. But point taken.
Regards.
Johan Potgieter said:
Anatoliy!!!!!
What are you trying to do? All those losses and leakage reactances! Are you that heavily against simple old UL?
Absolutely not!!!
I don't want to loose well regulated low voltage on screen grids, so in order to try advantages of UL I need separate UL windings...
Do you think, if you had separate windings for UL, you might be better served using them for cathode feedback à la Quad II instead of screen taps? I think that's what I would do, because it seems to give similar advantages to UL but with better damping, even if it does require more input from the driver.
There is a choice of OP trannies on the market that include separate UL/CF windings, such as Lundahl's LL1620_CFB, Sowter's U066 and 8994 and several Plitron/Amplimo designs.
Hey Ray,
There are several from Chicago's BO and BOH lines. A winder with a skilled unwinder( like Heyboer ) should have no problem making any one you decide to provide them a single sample of. The BO-6 is a fine OPT, and I'll soon know about their BO-14 too...🙂
cheers,
Douglas
There are several from Chicago's BO and BOH lines. A winder with a skilled unwinder( like Heyboer ) should have no problem making any one you decide to provide them a single sample of. The BO-6 is a fine OPT, and I'll soon know about their BO-14 too...🙂
cheers,
Douglas
ray_moth said:
Once again, I agree to try UL, but want to preserve freedom to use lower regulated G2 suppy 😀
Thank you!
I've ordered already some transformers from Edcor USA for prototyping, but probably Sowter may be another good option, though shipment from UK would be costly...
Just in support of these last posts.
It is probably remembered that that is what I do (Quad II style) - I have the great convenience of having a transformer firm on my doorstep, so to speak.
Only perhaps a warning: Even using 25% "taps" (that is the % cathode winding), leaves one with about 370Vp-p requirement on the power tube grids (6L6 in my case). One needs to watch out that the driver distortion does not become dominant (although for triodes it will be predominantly 2nd harmonic). I have since gone down to 20% windings. It takes me a little higher on the basic Rp scale, but still provides <1% distortion at 100W in my case, and eases the driver's job.
As Anatoliy suggested, one then has freedom to use lower G2 voltage, an advantage in high power tube amplifiers (also regulated).
Although importing is prohibitive because of cost for me, I am certainly going to look into the mentioned examples of output transformers. Thanks.
It is probably remembered that that is what I do (Quad II style) - I have the great convenience of having a transformer firm on my doorstep, so to speak.
Only perhaps a warning: Even using 25% "taps" (that is the % cathode winding), leaves one with about 370Vp-p requirement on the power tube grids (6L6 in my case). One needs to watch out that the driver distortion does not become dominant (although for triodes it will be predominantly 2nd harmonic). I have since gone down to 20% windings. It takes me a little higher on the basic Rp scale, but still provides <1% distortion at 100W in my case, and eases the driver's job.
As Anatoliy suggested, one then has freedom to use lower G2 voltage, an advantage in high power tube amplifiers (also regulated).
Although importing is prohibitive because of cost for me, I am certainly going to look into the mentioned examples of output transformers. Thanks.
Very interesting.... maybe I will try pentode mode with cathode feedback. I use 6L6's too, and I have more of them sitting around. I'm no tube expert, but this is a good way to learn.
Thanks for the ideas, guys!
Thanks for the ideas, guys!
Ken,
I should be in bed! But just a quick reminder. Cathode feedback with a pentode is in fact UL, if one analyses the topology. (The part of the transformer primary between g2 and B+, carrying cathode current, have simply been moved to the cathode side.) That brings more of triode performance into the circuit than pentode, which is part of the advantage.
Regards.
I should be in bed! But just a quick reminder. Cathode feedback with a pentode is in fact UL, if one analyses the topology. (The part of the transformer primary between g2 and B+, carrying cathode current, have simply been moved to the cathode side.) That brings more of triode performance into the circuit than pentode, which is part of the advantage.
Regards.
hey-Hey!!!,
Been thinking about special options with this topology. For a given CFB percentage, it is likely that building a tap in the plate winding of the same percentage will be easy( end of layer opportunities ). One can then ignore the tap, or use it in series to double the U-L percentage, or antiphase for true pentode operation with CFB. I must ratio the BO-14, as I suspect that it may be wound just this way...🙂
cheers,
Douglas
Been thinking about special options with this topology. For a given CFB percentage, it is likely that building a tap in the plate winding of the same percentage will be easy( end of layer opportunities ). One can then ignore the tap, or use it in series to double the U-L percentage, or antiphase for true pentode operation with CFB. I must ratio the BO-14, as I suspect that it may be wound just this way...🙂
cheers,
Douglas
Bandersnatch said:
I don't take any expert as the "last word" about anything. That also applies to Doug Self on the solid state side. Like Self, Crowhurst worked as a consultant to the "Big Box" manufacturers, and so wasn't in a position to rock the boat too much. So basically:
- Don't mindlessly follow fads
- The "numbers" don't tell all
- Even experts can be wrong
- Trust your judgement
ray_moth said:
a preferenc for dht's?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
my Cray XT4™ Supercomputer,
says 'UL is, obsolete'
or 'obstinate', which may be a glitch...
http://www.cray.com/downloads/Cray_XT4_Datasheet.pdf
http://www.cray.com/products/xt4/architecture.html
Ah, yes, but would you use UL with dhp (like a 47)?
How do you ask the Cray a question (e.g. What is the answer to the ultimate question of life, the universe and everything)?
How do you ask the Cray a question (e.g. What is the answer to the ultimate question of life, the universe and everything)?
Yes, Johan, I remember your telling us that. How long ago did you change from using screen taps (if you ever did) to using CFB?
Have you ever tried both at the same time, described as 'Super-Triode' in this article by Menno Van der Veen of Amplimo?
I understand that what you say is correct, but I believe the blanket term used for both is 'Distributed Load'.
Hi Ray,
Well ....🙂 I actually used both from early. I built a few Williamson and Leak TL12 types (triodes) for folks desiring them, but I experienced the first Quad II at about 1955 (imported by a friend) and got behind the topology by Peter Walker actually sending me a copy of his and Williamson's article now well known. For Quad types the output transformers had to be wound locally and were more expensive than UL types off the shelf. So I did the Quad type only where the client did not mind paying. The first one was a 150W mono (4 x KT66) about 1957, used as a PA/hi-fi amp. Usual requirements were for 30 - 40W types, screen taps, EL34/KT66/6L6GB. (*GCs down here came later.) (At the time I mostly used the pentode-ltp-triodes type pre-circuit, but cathode feedback required Williamson types.)
Yes, I actually prefer the term distributed load, also for screen taps. (Not to be as adamant as Williamson/Walker, but ultra- linear is not an exact feature - it is not really "more linear".) But UL has become easy and well-known. Few would know what DL is.
V.d.Veen's article is interesting indeed, as is his test circuit. He unfortunately does not give distortion analysis. Intuitively I would not prefer the "super-pentode" (only for a few watts extra?) - would like to check max. dissipation and distortion first. The "super-triode" solves the problem mentioned earlier of best screen taps rendering too much cathode feedback, thus drive signal. Quad II actually suffers somewhat by using only a 10% "tap" (i.e. cathode winding). I did say that I came down to 20% (from 25%) for reasons of drive convenience. The super-triode also means that one is back to anode potential on G2. (Not another separate G2-winding, please!
)
Regards
Well ....🙂 I actually used both from early. I built a few Williamson and Leak TL12 types (triodes) for folks desiring them, but I experienced the first Quad II at about 1955 (imported by a friend) and got behind the topology by Peter Walker actually sending me a copy of his and Williamson's article now well known. For Quad types the output transformers had to be wound locally and were more expensive than UL types off the shelf. So I did the Quad type only where the client did not mind paying. The first one was a 150W mono (4 x KT66) about 1957, used as a PA/hi-fi amp. Usual requirements were for 30 - 40W types, screen taps, EL34/KT66/6L6GB. (*GCs down here came later.) (At the time I mostly used the pentode-ltp-triodes type pre-circuit, but cathode feedback required Williamson types.)
Yes, I actually prefer the term distributed load, also for screen taps. (Not to be as adamant as Williamson/Walker, but ultra- linear is not an exact feature - it is not really "more linear".) But UL has become easy and well-known. Few would know what DL is.
V.d.Veen's article is interesting indeed, as is his test circuit. He unfortunately does not give distortion analysis. Intuitively I would not prefer the "super-pentode" (only for a few watts extra?) - would like to check max. dissipation and distortion first. The "super-triode" solves the problem mentioned earlier of best screen taps rendering too much cathode feedback, thus drive signal. Quad II actually suffers somewhat by using only a 10% "tap" (i.e. cathode winding). I did say that I came down to 20% (from 25%) for reasons of drive convenience. The super-triode also means that one is back to anode potential on G2. (Not another separate G2-winding, please!
)Regards
Thanks, Johan. When you say that 'Super-Triode' solves the problem of best screen taps rendering too much cathode feedback, I guess you mean that the NFB can be shared between cathode feedback and screen taps feedback? Since only the CF part increases the driver signal requirements, you could 'have your cake and eat it'.
I guess, also, that the reason you found you needed to use Williamson topology for CF was because the 'Leak/Mullard' topology couldn't give sufficient swing?
I guess, also, that the reason you found you needed to use Williamson topology for CF was because the 'Leak/Mullard' topology couldn't give sufficient swing?
ray_moth said:
That is correct. I am at present looking at my output transformer design to see if such G2-taps will conveniently lie at the end of layers. For me (6L6) that would mean ability to go for say 35% G2-taps, and using only say 15 - 20% of the total primary in the cathode circuit. It would probably mean a bit of juggling to satisfy other OPT requirements. (I use Langford-Smith design procedures - originator Crowhurst again!)
Correct again, plus also more gain required. I have an input pentode-to-cathodyne phase splitter (ECF80 or the like), folllowed by a fairly hefty twin triode (E182CC) to get the about 370Vpp 6L6 grid drive at fairly low output impedance, as mentioned before. I am not saying it would be impossible with the L/M topology, but I found that inconvenient. (I like that for "normal" designs.) With the above and 20dB global NFB input needed is about 400mV.
Regards.
On this CFB drive level...370V p-p seems a bit high, even at 20%. May I assume AB1? Say a 6L6's g1 is 50V negative. Half of 370 is 185V. 185-50 is 135. 135/.2 is 675 V worth of anode swing(per phase ).
Are you sure you're doing the math corectly? Or could you point out where I made an error?
My KT90 amp from long ago ran the Dynaco A441( a rather mediocre OPT ). B+ of 375 and idle current of 115 mA per tube needed about +/- 90V of swing IIRC. That one had ~16% CFB.
cheers,
Douglas
Are you sure you're doing the math corectly? Or could you point out where I made an error?
My KT90 amp from long ago ran the Dynaco A441( a rather mediocre OPT ). B+ of 375 and idle current of 115 mA per tube needed about +/- 90V of swing IIRC. That one had ~16% CFB.
cheers,
Douglas
Johan Potgieter said:
Hi Johan, had to think about that one for a while but I don't quite see it. UL doesn't modulate the cathode/grid voltage, cathode feedback does and typically derives the bulk of its degeneration from it. The latter has UL aspects by modulating the cathode/screen voltage but true equivalence escapes me.
rdf said:
Ignore the magnitude of the FB for a moment.
Fix g2 voltage as for 'pentode' CFB operation. The cathode is moved a percentage of the anode swing. since g2 is fixed, k-g2 gets moved the same percentage. Now it isn't the magic 43% due to the tertiary winding usually being a single layer on either side of CT.
cheers,
Douglas
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