Agreed
Hi Jan,
Agreed. And I should have been more clear. I was referring to some who believe they already have the best designs, and not give another a chance, such as vdV. There is alot of uncharted territory out there so pinning this or that design as best is a little premature in my opinion.
I was thinking if it was his First project, this might be a little difficult for him, but in no way meaning to put either him or vdV down. Just thinking one should completely understand, If he is a newbie, so one wouldn't get frustrated if something doesn't work quite right and throw up his hands in disgust.
Sorry about any confusion Jan.
Hi Jan,
Agreed. And I should have been more clear. I was referring to some who believe they already have the best designs, and not give another a chance, such as vdV. There is alot of uncharted territory out there so pinning this or that design as best is a little premature in my opinion.
I was thinking if it was his First project, this might be a little difficult for him, but in no way meaning to put either him or vdV down. Just thinking one should completely understand, If he is a newbie, so one wouldn't get frustrated if something doesn't work quite right and throw up his hands in disgust.
Sorry about any confusion Jan.
What Specific Alternatives Can You Recommend?
Thanks all, for your variety of insights and viewpoints.
A number have suggested that I tackle a more conventional, proven design for my next project. That seems a very reasonable suggestion--could I trouble you to give me specific examples of what you have in mind? Can you recommend an available 50+WPC DIY design that sounds great?
A schematic (with layout and parts list would be ideal) or kit would be fine, and I am glad to pay for a good design.
I've suggested a couple of designs, and appreciate your cautions / reservations on them. If you share specific recommendations of what you *like*, you'll help a newbie build something better.
Save me from the cluches of unproven design!
Thanks again, and happy building!
Best,
George Ferguson
Thanks all, for your variety of insights and viewpoints.
A number have suggested that I tackle a more conventional, proven design for my next project. That seems a very reasonable suggestion--could I trouble you to give me specific examples of what you have in mind? Can you recommend an available 50+WPC DIY design that sounds great?
A schematic (with layout and parts list would be ideal) or kit would be fine, and I am glad to pay for a good design.
I've suggested a couple of designs, and appreciate your cautions / reservations on them. If you share specific recommendations of what you *like*, you'll help a newbie build something better.
Save me from the cluches of unproven design!
Thanks again, and happy building!
Best,
George Ferguson
More Info / Question on the Vanderveen Design
Hi All,
I was re-reading MV's article on constructing the Super-Triode circuit (here) , and I noticed that for best sound he recommends running the SV6550C at 75mA per tube.
He says that he realizes that this high quiescent current will shorten tube life, but that he finds the tradeoff worthwhile for better sound (the details are at the end of the article).
Can anyone give me an idea of how short a tube life one could expect from a SV6550C at 75mA quiescent current? How hard is that pushing the tube?
Thanks all!
George Ferguson
Hi All,
I was re-reading MV's article on constructing the Super-Triode circuit (here) , and I noticed that for best sound he recommends running the SV6550C at 75mA per tube.
He says that he realizes that this high quiescent current will shorten tube life, but that he finds the tradeoff worthwhile for better sound (the details are at the end of the article).
Can anyone give me an idea of how short a tube life one could expect from a SV6550C at 75mA quiescent current? How hard is that pushing the tube?
Thanks all!
George Ferguson
Thoughts
Hi Doc,
Got some thoughts about some things.
1) I would guess the tube, at .075a is probably dissapating close to 94-97% of the dissapation rating.
2) The power supply shown has some major drawbacks and I wouldn't recommend it.
The main problem is frequency dependent music/sonic feedback through the power supply. It is occurring at midband and much worse as the frequency goes lower, with phase shifts approaching approx 90 degrees between ajacent channels. Clearly not good, but inexpensive. Sound won't be that clean when such a supply is used.
When using feedback "from" an OPT, the requirements of the OPT are enormous; much greater than the requirements when no feedback is used.
His findings of DF in triode mode seems low to me. In triode mode, damping factors can be 8 or more without the use of negative feedback.
ps. By the way, fig 4, 5 have to be designed very carefully and clipping minimized if the screens are to be kept intact.
Hi Doc,
Got some thoughts about some things.
1) I would guess the tube, at .075a is probably dissapating close to 94-97% of the dissapation rating.
2) The power supply shown has some major drawbacks and I wouldn't recommend it.
The main problem is frequency dependent music/sonic feedback through the power supply. It is occurring at midband and much worse as the frequency goes lower, with phase shifts approaching approx 90 degrees between ajacent channels. Clearly not good, but inexpensive. Sound won't be that clean when such a supply is used.
When using feedback "from" an OPT, the requirements of the OPT are enormous; much greater than the requirements when no feedback is used.
His findings of DF in triode mode seems low to me. In triode mode, damping factors can be 8 or more without the use of negative feedback.
ps. By the way, fig 4, 5 have to be designed very carefully and clipping minimized if the screens are to be kept intact.
Hi George, All,
In the othwewise extensive documentation of http://www.plitron.com/PDF/4070CFB.PDF I am not able to find the windings ratio for the Cathode Feedback. Is this a problem of my bad sight or is this considered to be a trade secret?
Regards,
Peter Jacobi
DrDeville said:
In the othwewise extensive documentation of http://www.plitron.com/PDF/4070CFB.PDF I am not able to find the windings ratio for the Cathode Feedback. Is this a problem of my bad sight or is this considered to be a trade secret?
Regards,
Peter Jacobi
Cathode Feedback is 7.1%
Hi Peter,
I think I can help you out--I guess it's easier to be a realtive expert on something no one seems to know much about
Anyway, the answer to your questions is "no".
The Amplimo site has different documentation than the Plitron site, and the information you seek is here --7.1%.
The Plitron site has more links to projects using the transformers (click on the "site map" link), and the Amplimo site seems to have better transformer descriptions, including explanations on what the model designations mean.
I hope this helps, and happy tweaking!
Best,
George Ferguson
Hi Peter,
I think I can help you out--I guess it's easier to be a realtive expert on something no one seems to know much about
Anyway, the answer to your questions is "no".
The Amplimo site has different documentation than the Plitron site, and the information you seek is here --7.1%.
The Plitron site has more links to projects using the transformers (click on the "site map" link), and the Amplimo site seems to have better transformer descriptions, including explanations on what the model designations mean.
I hope this helps, and happy tweaking!
Best,
George Ferguson
This is my dream thread, I am too going along the same path as this thread starter Plitron and vdV...
I am Quite stunned to the feedback and good measure this design has had so far, and are even more stunned that no one replied to the thread I started a few months back upon the 4142 and KT88.
I guess there is something special about cathode feedback..
and there isn't much new in this design which credits such comments..:
http://www.plitron.com/pages/Products/Audio/vtvkt88.htm
I am very happy of the comments you guy's have given this guy and have forever more been fortified to get this amplifier built and working well now since upon reading this thread.
Can I expect similar quality if the Plitron 4142 designed by vdV?
I too am learning more and more everyday about how and why certian methods are used like using the plate for input instead of grid or cathode in rectifiers for a lower resistive output, I think.
And how fixed and variable bias has different effects and reasons.
I've been flying through old Electronics Australia magazines and Radio Constructor from england and reading all of the theorys and project ideas like they're today's news
Surprisingly to me I can actually now understand 1/2 of the "Manual of Questions & Answers for the novice licence" Sixth Edition, January 1978
I've been working for years for my Amateur Radio Operators licence but not once went in for a test because I know myself I am still not cut out for it, (I want to go in there first time and get it off the bat).
But I /still/ can't seem to get enough time with a good read
Diyaudio.com has been a great help in many areas Thanks!
I am Quite stunned to the feedback and good measure this design has had so far, and are even more stunned that no one replied to the thread I started a few months back upon the 4142 and KT88.
I guess there is something special about cathode feedback..
and there isn't much new in this design which credits such comments..:
http://www.plitron.com/pages/Products/Audio/vtvkt88.htm
I am very happy of the comments you guy's have given this guy and have forever more been fortified to get this amplifier built and working well now since upon reading this thread.
Can I expect similar quality if the Plitron 4142 designed by vdV?
I too am learning more and more everyday about how and why certian methods are used like using the plate for input instead of grid or cathode in rectifiers for a lower resistive output, I think.
And how fixed and variable bias has different effects and reasons.
I've been flying through old Electronics Australia magazines and Radio Constructor from england and reading all of the theorys and project ideas like they're today's news
Surprisingly to me I can actually now understand 1/2 of the "Manual of Questions & Answers for the novice licence" Sixth Edition, January 1978
I've been working for years for my Amateur Radio Operators licence but not once went in for a test because I know myself I am still not cut out for it, (I want to go in there first time and get it off the bat).
But I /still/ can't seem to get enough time with a good read
Diyaudio.com has been a great help in many areas
Thanks!
See? Sometimes dreams *do* come true.
Ah, another Thermonic Thrillseeker! Welcome!
From the article you mentioned and comments here, the KT88 design you mentioned is a straightforward and euphonic update of a traditional design, with the MvdV transformer being the biggest change. As you read, VTV loved it and Plitron (which implies MvdV) assisted, if that gives you any confidence.
A major drawback of MvdV's torroidal transformers is their saturation sensitivity to DC. However, it looks like this design takes that into account with the bias adjustments. check this thread for further comments and considerations, and discussion of a less traditional MdvV design. And if you can't read enough, you might pick up his book.
I'm working on his Super-Triode amplifier, so feel free to contact me if this newbie can be of any help, even if it's just encouragement.
Good luck!
Best,
George Ferguson
Thank you DrDeville!! for commenting!
Yes! I actually found a website while searching for the willamson design where it said there simply "Don't mix circuit plans, choose one and stick to that one, e.g. don't try fixed bias with a Williamson."
It was from here: http://www.xs4all.nl/~ideas/amps/chapt14.html
I haven't read it very much if at all...I'm currently busy sanding back some shelfs for my new kick-*** mini-workbench
Will do check that thread, His book!? As long as I can get it in hard-cover
I'll post pictures, it's going to be fully polished with natural shellac to give a really outstanding look for the otherwise dull pure-white room, I love polished woodwork but hate to see trees like this...
Kind of a catch 20
for commenting!Yes! I actually found a website while searching for the willamson design where it said there simply "Don't mix circuit plans, choose one and stick to that one, e.g. don't try fixed bias with a Williamson."
It was from here: http://www.xs4all.nl/~ideas/amps/chapt14.html
I haven't read it very much if at all...I'm currently busy sanding back some shelfs for my new kick-*** mini-workbench
Will do check that thread, His book!? As long as I can get it in hard-cover
I'll post pictures, it's going to be fully polished with natural shellac to give a really outstanding look for the otherwise dull pure-white room, I love polished woodwork but hate to see trees like this...
Kind of a catch 20
Hi George,
Would yoz be so kind to further clarify one point:
Is this problem really limited to DC and how does the transformer know, it's DC?
To make this sound less insane, I try to give an example.
Assume you are reproducing music at significant level, say 10W.
Now the organ plays the C (65Hz, if I remember right). This is pretty near to DC, so to say. The mA representing this "C" will flow for 120° (about 5ms) in one direction at significant amplitude.
Will this saturate the core and disturb all other tones, i.e. producing large IM distortion?
Regards,
Peter Jacobi
Would yoz be so kind to further clarify one point:
DrDeville said:
Is this problem really limited to DC and how does the transformer know, it's DC?
To make this sound less insane, I try to give an example.
Assume you are reproducing music at significant level, say 10W.
Now the organ plays the C (65Hz, if I remember right). This is pretty near to DC, so to say. The mA representing this "C" will flow for 120° (about 5ms) in one direction at significant amplitude.
Will this saturate the core and disturb all other tones, i.e. producing large IM distortion?
Regards,
Peter Jacobi
Hi Peter,
Thanks for your question! Sometimes when I say that I am just being polite, but this time I mean it, because your question seems like a sincere search for knowledge, a quest I enjoy.
Anyway, I was lucky enough to get Menno Vanderveen's book today, and after glancing at it, I will try to answer your questions. Please bear in mind that I am a newbie, may make mistakes, and appreciate anyone's corrections.
Okay, here goes:
As far as I can tell, your physics and intuition are correct. Any transformer is will saturate at too high a current and, except for a factor I will mention, it does not matter whether the current is AC or DC.
Of course, as frequency goes down, the peak voltage/current required to produce a given power level goes up, so this factor becomes more of a constraint as frequency goes down.
Here's an example from MvdV's book. Take a SET circuit ( Class A natch), and an Amplimo/Plitron VDV3035-SE transformer, designed for single-ended circuits. Its rated maximum DC current with low distortion is Idc = 173 mA. As you correctly noted, this maximum current must be shared between DC and the music, so MvdV recommends setting the tube quiescent current at 0.5*Idc, allowing the greatest current swing on the output signal before exceeding the transformer's rating.
Make sense?
Another consideration (for input stages at least, I'm not sure about output transformers) is that in PP amps AC music signals go through the transformer in opposite directions, so their magnetic fields cancel out and do not contribute to transformer saturation!
So in summary, your concern is a correct one, but not a problem as long as the transformer is operated within its rated current limits.
I believe this is true of *any* transformer. However, torroidal transformers tend to have lower saturation current limits, so the design must take that into account--e.g. a design for a torroidal transformer might control DC transformer current more carefully than a corresponding air-gap transformer circuit.
Why bother? Well, everything is a tradeoff, and torroidal transformers trade DC suceptibility for lower distortion and greater bandwidth.
If you'd like to see an example, check out this article from VTV, which presents an amp that updates a Williamson circuit to work with a Plitron/Amplimo transformer. They thought the Plitron torroid performed as well or better than one of the best classic transformers--the Acrosound TO-330.
Anyway, I hope you find this mesage useful--I certainly learned while writing it.
Apologies in advance for any mistakes or insults--either is unintentional.
Happy Building,
George Ferguson
Thanks for your question! Sometimes when I say that I am just being polite
, but this time I mean it, because your question seems like a sincere search for knowledge, a quest I enjoy. Anyway, I was lucky enough to get Menno Vanderveen's book today, and after glancing at it, I will try to answer your questions. Please bear in mind that I am a newbie, may make mistakes, and appreciate anyone's corrections.
Okay, here goes:
As far as I can tell, your physics and intuition are correct. Any transformer is will saturate at too high a current and, except for a factor I will mention, it does not matter whether the current is AC or DC.
Of course, as frequency goes down, the peak voltage/current required to produce a given power level goes up, so this factor becomes more of a constraint as frequency goes down.
Here's an example from MvdV's book. Take a SET circuit ( Class A natch), and an Amplimo/Plitron VDV3035-SE transformer, designed for single-ended circuits. Its rated maximum DC current with low distortion is Idc = 173 mA. As you correctly noted, this maximum current must be shared between DC and the music, so MvdV recommends setting the tube quiescent current at 0.5*Idc, allowing the greatest current swing on the output signal before exceeding the transformer's rating.
Make sense?
Another consideration (for input stages at least, I'm not sure about output transformers) is that in PP amps AC music signals go through the transformer in opposite directions, so their magnetic fields cancel out and do not contribute to transformer saturation!
So in summary, your concern is a correct one, but not a problem as long as the transformer is operated within its rated current limits.
I believe this is true of *any* transformer. However, torroidal transformers tend to have lower saturation current limits, so the design must take that into account--e.g. a design for a torroidal transformer might control DC transformer current more carefully than a corresponding air-gap transformer circuit.
Why bother? Well, everything is a tradeoff, and torroidal transformers trade DC suceptibility for lower distortion and greater bandwidth.
If you'd like to see an example, check out this article from VTV, which presents an amp that updates a Williamson circuit to work with a Plitron/Amplimo transformer. They thought the Plitron torroid performed as well or better than one of the best classic transformers--the Acrosound TO-330.
Anyway, I hope you find this mesage useful--I certainly learned while writing it.
Apologies in advance for any mistakes or insults--either is unintentional.
Happy Building,
George Ferguson
I believe that the MacIntosh Amps used a cathode winding coupled to the output transformer. It was considered to be a major break through because it allows the tube grid currents to keeps the OPT core flux from going to zero. This eliminates crossover distortion.
All of this is explained in MvdV's supplement to his book. The transformers are better designs then have been available for years. If you are interested in cathode coupling they are the only option. That doesn't mean that the MvdV Amp circuit designs are the best possible. He recommends many things I would do differently. This probably means that It should not be a first amp, or if it is, you should be ready to change things. These devices are 1. Expensive and 2. Potentally lethal. MvdV explains that the ul cathode coupled design is limited by it's voltage drive requirements.
I personally would copy an old Mac design using the Plitron transformers and other modern components.
Just another $0.02.
All of this is explained in MvdV's supplement to his book. The transformers are better designs then have been available for years. If you are interested in cathode coupling they are the only option. That doesn't mean that the MvdV Amp circuit designs are the best possible. He recommends many things I would do differently. This probably means that It should not be a first amp, or if it is, you should be ready to change things. These devices are 1. Expensive and 2. Potentally lethal. MvdV explains that the ul cathode coupled design is limited by it's voltage drive requirements.
I personally would copy an old Mac design using the Plitron transformers and other modern components.
Just another $0.02.
DrDeville said:
Amplio is van der Veen's company and Plitron hired him to be their head transformer designer (and they spent a fair amount of Canada Research Council grants)
I spent a good part of an afternoon listening to him and Bill Perkins talk about transformers. Both these guys know a lot about transformer design.
As to an amp you might look at Allen Wright's amp ... with 4 KT88s or 2 509s (i think it was these 5xx somethings anyway-- Allen was talking about 4 tubes for 100 W to drive some new ESLs he'd fallen head ove heels for) you should be able to get 50 W or so.
An externally hosted image should be here but it was not working when we last tested it.
It uses the cascode differential front end (his twist on stuff HP used in test gear) and a Class A triode wired output stage with a CCS on the cathodes. Allen publically revealed the circuit at the most recent VSAC (the reason why is an interesting story in itself). Allen has only found one other amp using similar tricks -- used in a atomic electric plant (what for i don't know), but he will be the 1st to admit there is little new... he hadn't seen the precursor to his amp pictured (from 1956 Radio Electonics). Take that amp, wire in triode, bias into class A, add CCSs at the bottom of both differential sections, a super reg on the cascode, no feedback, and you have the essence of his amp.
It is available as a kit if you don't want to tackle all the fine tuning he has done over the last 6 or more years.
dave
Attachments
Thomas said:
As I said above, that's an intriguing idea.
I did a little Googling around--is this the sort of thing you had in mind?
Just checking--I like your idea, but just wonder if there might be a simpler version.
Thanks again--because of help from folks like you, I am beginning to get some ideas on how to begin what I hope will be a long and fun journey.
Best,
George Ferguson
As I said above, that's an intriguing idea.
I did a little Googling around--is this the sort of thing you had in mind?
Just checking--I like your idea, but just wonder if there might be a simpler version.
Thanks again--because of help from folks like you, I am beginning to get some ideas on how to begin what I hope will be a long and fun journey.
Best,
George Ferguson
Planet10 wrote:
Hey Dave,
Thanks for the tip. I like the ideas behind the amp, and love the cosmetics. I am a total sucker for that updated 50s "Forbidden Planet" look. Mondo cool.
Anyway, I sent Vacuum State Electronics an email to check on the price of their kits. I plan to be sitting when I read it, for their assembled units are on sale for 8800 euros!
(I have Scottish and Dutch ancestry, so frugality is deep in my genes 
)
Thanks again for the tip--each one give me new ideas. I like his idea for removing the distortion that PP amps may have at very low signal levels. Seems the McIntosh cathode feedback design was another solution to the same issue.
Happy Tweaking,
George Ferguson
Hey Dave,
Thanks for the tip. I like the ideas behind the amp, and love the cosmetics. I am a total sucker for that updated 50s "Forbidden Planet" look. Mondo cool.
Anyway, I sent Vacuum State Electronics an email to check on the price of their kits. I plan to be sitting when I read it, for their assembled units are on sale for 8800 euros!
(I have Scottish and Dutch ancestry, so frugality is deep in my genes )Thanks again for the tip--each one give me new ideas. I like his idea for removing the distortion that PP amps may have at very low signal levels. Seems the McIntosh cathode feedback design was another solution to the same issue.
Happy Tweaking,
George Ferguson
Allen Wright Differential Amp
Planet10 Wrote:
My goal is to first build a baseline 50WPC amp, and then, as I learn, modify it into something fantastic sounding.
One apt truism is "Any successful device is a modification of a simpler one." So I'm hoping to select a topology that I can build in a simple/traditional form, get working, and then improve--Like maybe PP, and then do something tricky to combat crossover effects.
That possibility attracts me to Menno Vanderveen's cathode-feedback designs, and it seems like Allen Wright's Differential amp design might offer a similar opportunity.
Planet10 Wrote:
Okay, I just... D'OH!
Seriously, do you think it would be possible to start with a relatively straighforward PP design and then, with the help of a wise mentor
, slowly modify it into something like Wright's design, or something equally cool?
(If you say "yes", you know what my next question will be.)
By the way, I checked out Allen Wright's kits and, though they are wonderful and probably worth every penny, they look a bit beyond my budget as a starting point.
But again thanks for the tip and the food for thought.
Best,
George Ferguson
Planet10 Wrote:
Thanks Dave. I did, am intrigued, and would enjoy any opinions/insights that you or others have about it.
My goal is to first build a baseline 50WPC amp, and then, as I learn, modify it into something fantastic sounding.
One apt truism is "Any successful device is a modification of a simpler one." So I'm hoping to select a topology that I can build in a simple/traditional form, get working, and then improve--Like maybe PP, and then do something tricky to combat crossover effects.
That possibility attracts me to Menno Vanderveen's cathode-feedback designs, and it seems like Allen Wright's Differential amp design might offer a similar opportunity.
Planet10 Wrote:
Okay, I just... D'OH!
Seriously, do you think it would be possible to start with a relatively straighforward PP design and then, with the help of a wise mentor
, slowly modify it into something like Wright's design, or something equally cool?(If you say "yes", you know what my next question will be.)
By the way, I checked out Allen Wright's kits and, though they are wonderful and probably worth every penny, they look a bit beyond my budget as a starting point.
But again thanks for the tip and the food for thought.
Best,
George Ferguson