I don´t agree that screen drive produces triode curves, looks more like ultra linear or penthode to me.
However, I tested my monoblocks less than an hour ago and they seemed perfectly happy with 2,5k
Once the mechanical assembly is completed I´ll sit down and try to find the best operation point, I guess that with 2,5k it will be "low and hot"
However, I tested my monoblocks less than an hour ago and they seemed perfectly happy with 2,5k
Once the mechanical assembly is completed I´ll sit down and try to find the best operation point, I guess that with 2,5k it will be "low and hot"
hi all
i thought i would try to resserect this thread as i have built a ear 859 se clone but i need some help/advice.
i find the top end very rolled off,i noticed that someone mentions a printing error in the schematic regarding the feedback loop,ive built using 47pf x2 per channel in the feedback loop,is this my problem and should they be infact 4.7pf,would this re -address the treble issue? also i wanted to use silver micra in this postion but they only seem to go up to 500volts rating as in the diagram its showing 600+? is that right or can i get away with 500v rating.
would love to hear anyones views/experiences regarding building and using this amp along with ideas and tweaks,and ideas and surgesstions regarding output transformers as im using r-cores of unknown make quality or specs.
please help
all the best
smithie
i thought i would try to resserect this thread as i have built a ear 859 se clone but i need some help/advice.
i find the top end very rolled off,i noticed that someone mentions a printing error in the schematic regarding the feedback loop,ive built using 47pf x2 per channel in the feedback loop,is this my problem and should they be infact 4.7pf,would this re -address the treble issue? also i wanted to use silver micra in this postion but they only seem to go up to 500volts rating as in the diagram its showing 600+? is that right or can i get away with 500v rating.
would love to hear anyones views/experiences regarding building and using this amp along with ideas and tweaks,and ideas and surgesstions regarding output transformers as im using r-cores of unknown make quality or specs.
please help
all the best
smithie
I found 4.7pF worked well and assumed this was one of the errors referred to.
As for voltage rating, the peak on the anode could theoretically reach twice the HT volts, so I would use high voltage components to be on the safe side. I think the OPT primary was about 6k8 gapped for 90mA, but I might be wrong about that as it was a long time ago.
As for voltage rating, the peak on the anode could theoretically reach twice the HT volts, so I would use high voltage components to be on the safe side. I think the OPT primary was about 6k8 gapped for 90mA, but I might be wrong about that as it was a long time ago.
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hi ardee
thanks very much for your reply and infomation, regarding the pf voltage on the feedback,i knew deep down i wouldnt get away with the lower voltage...i was just hoping as i dont quite know what to use there for good results,plenty to choose up to 500v but in the 630v range there isnt much..any surgestions/links to something suitable would be of help,i can follow a curcuit just but have little understanding why im doing things.
its a shame you not deffient regarding the opts as i would really like to get that right,you reckon 6k8 yet someone before in this thread gave a value of 4k6...damn,anyone know for sure,but whatever i appricate your help thus far
all the best
smithie
thanks very much for your reply and infomation, regarding the pf voltage on the feedback,i knew deep down i wouldnt get away with the lower voltage...i was just hoping as i dont quite know what to use there for good results,plenty to choose up to 500v but in the 630v range there isnt much..any surgestions/links to something suitable would be of help,i can follow a curcuit just but have little understanding why im doing things.
its a shame you not deffient regarding the opts as i would really like to get that right,you reckon 6k8 yet someone before in this thread gave a value of 4k6
...damn,anyone know for sure,but whatever i appricate your help thus farall the best
smithie
The roll-off capacitors will not be working within the audio range, so I personally would have no problem using high voltage ceramics from Cricklewood Electronics.
Although the curves are triode-like, screen drive gives a pentode-like ra so I would not make the load too low. Whatever you use is very unlikely to perform as well as the original, and I think I got my figure by measuring the voltage ratio of one of these.
Although the curves are triode-like, screen drive gives a pentode-like ra so I would not make the load too low. Whatever you use is very unlikely to perform as well as the original, and I think I got my figure by measuring the voltage ratio of one of these.
The output Transformer impedance on the primary is nominally 5K Ohm.
The capacitors used in my product are 47 pf and are 500 volt Mica or were Philips 630 volt Polyprop (now discontinued) Ceramics produce non linear distortion, I never use them if I can help it.
The combined 23.5 pf was for stability with capacitance load on the speaker side. You might have reduced the value due to a poor output transformer and wishing to make 20 KHz ruler flat, Not my minus a half dB,
Farnell do have some 47 pf at 1000 volt polyprop capacitors now.
As an alternative, you could as I have done in the past use a piece of RG178
coax at 103 pf per metre, good for 3KV peak.
Anyone can offer different circuits and can be so smart after the fact.
I have to consider value for money in a design. Would someone pay a million Dollars for the product? No. However, there are over a thousand units
sold in Japan let alone else where. That is reality I affraid.
AV8R
hi guys
many thanks for your input and help,much appricated.
av8r...many thanks for your valued input and clearing my questions up for me,i heard your original product when it was first introduced,had one for awhile but like a idiot i sold it on when my hifi fix kicked in, over the years ive learnt what a big mistake that was.
as i had the circuit diagram and wanted to learn alittle and try to build something this amp seemed the ideal choice.
is it still possible to buy the originall transformer kit that you offered in the original hifi news magazine?ive been on the look out for some that may have never been used when brought for a kit...but to no avail.
once again many thanks to everyone.
all the best
smithie
many thanks for your input and help,much appricated.
av8r...many thanks for your valued input and clearing my questions up for me,i heard your original product when it was first introduced,had one for awhile but like a idiot i sold it on when my hifi fix kicked in, over the years ive learnt what a big mistake that was.
as i had the circuit diagram and wanted to learn alittle and try to build something this amp seemed the ideal choice.
is it still possible to buy the originall transformer kit that you offered in the original hifi news magazine?ive been on the look out for some that may have never been used when brought for a kit...but to no avail.
once again many thanks to everyone.
all the best
smithie
Congratulations for your amp.
Could you share your experiences on all (intentional?) error related to schematics published by HFN? I have been aware of 2 errors so far, 47 k instaed of 4.7k and 4.7 pF instaed of 47 pF...there must be others I'm interested so much.
Errors?
Hi, Sorry Obi, I was not aware of any errors. I built my amp to the circuit diagrams published in 1994 in HFN. On the magazine copy I have here I can see there are 2x 47pH caps in series on the anode of the PL519 (I used 40V heater valves) but otherwise I know of no errors I'm afraid. I'll be interested to know if there any mistakes in the original article???
I guess I could compare the diagram published on the web with my paper copy? Please do let me know if you find anything, I'll have a look over the web diagram in the next couple of days.
Thanks, Andrew
Hi, Sorry Obi, I was not aware of any errors. I built my amp to the circuit diagrams published in 1994 in HFN. On the magazine copy I have here I can see there are 2x 47pH caps in series on the anode of the PL519 (I used 40V heater valves) but otherwise I know of no errors I'm afraid. I'll be interested to know if there any mistakes in the original article???
I guess I could compare the diagram published on the web with my paper copy? Please do let me know if you find anything, I'll have a look over the web diagram in the next couple of days.
Thanks, Andrew
Hi guys, long no see .. how about this re-calculated design of the original 859 for some other tube types ? (The 2x47pF -s will be adjusted to 4.7pF)
Made by my father, we're already working on a further upgrade with XLR/balanced inputs.
Made by my father, we're already working on a further upgrade with XLR/balanced inputs.
An externally hosted image should be here but it was not working when we last tested it.
EAR859,
Obi Wan, There is no error, I stated 47 pf with two in series making 23.5 pf.
Please I did this to make good stability into high capacitance loads such as QUAD ELS speakers.
I did state minus half dB at 20 KHz Of which I am sure you golden ears lot can hear perfectly every time?
Upgrade yes what does this word mean? like Balanced input by what means?
Not an upgrade in the home. KT88 can be made to work but requires way to much drive to be able to get full output. I stated 20 years ago that the EL509 or PL509/519 are ideal for this, Oh and linearity is superb thank you.
My later version with an added extra valve to make it bias accurately without selecting valves added cost to original.
It was made to an affordable price point, Hence the world wide success.
My question is "How long is a piece of string?"
Finally, trying to add motional feedback is not very clever as there is precious little spare gain. The feedback in the original is only 7 dB.
All deliberate in the original design of mine.
Obi Wan, There is no error, I stated 47 pf with two in series making 23.5 pf.
Please I did this to make good stability into high capacitance loads such as QUAD ELS speakers.
I did state minus half dB at 20 KHz Of which I am sure you golden ears lot can hear perfectly every time?
Upgrade yes what does this word mean? like Balanced input by what means?
Not an upgrade in the home. KT88 can be made to work but requires way to much drive to be able to get full output. I stated 20 years ago that the EL509 or PL509/519 are ideal for this, Oh and linearity is superb thank you.
My later version with an added extra valve to make it bias accurately without selecting valves added cost to original.
It was made to an affordable price point, Hence the world wide success.
My question is "How long is a piece of string?"
Finally, trying to add motional feedback is not very clever as there is precious little spare gain. The feedback in the original is only 7 dB.
All deliberate in the original design of mine.
Well, we'll try this last design anyway and let's see how it performs.
The core principle was to play around a little bit and experiment, not to meet or match the original 859's performance - that does't matter anymore for now, at least we're not comparing our own project to that. It served as a very interesting design (and basis) for the enhanced triode mode operation, but that's all. The rest is all about having fun since we're both hobbyists.. I'll be happy if we can finish this very first amp of mine this year..
Here's the - most probably - final one, fresh as of today (we haven't read your comments yet, however, thanks for the observations).
I try to translate comments into English:
1. XLR input added.
2. Grid voltage has been increased so the tube operates in a more steep and more linear section compared to our very first KT88 design.
3. Feedback has been simplified (again compared to the very first design) and will be set up based on our experiments with the final boxes.
4. If we put everything into one chassis like usual (instead of 2 monoblocks) we can use 1+1 remaining half of the 2 ECC99 tubes for something else - thinking about a separate headphone circuit now.. not sure yet.
The core principle was to play around a little bit and experiment, not to meet or match the original 859's performance - that does't matter anymore for now, at least we're not comparing our own project to that. It served as a very interesting design (and basis) for the enhanced triode mode operation, but that's all. The rest is all about having fun since we're both hobbyists.. I'll be happy if we can finish this very first amp of mine this year..
Here's the - most probably - final one, fresh as of today (we haven't read your comments yet, however, thanks for the observations).
An externally hosted image should be here but it was not working when we last tested it.
I try to translate comments into English:
1. XLR input added.
2. Grid voltage has been increased so the tube operates in a more steep and more linear section compared to our very first KT88 design.
3. Feedback has been simplified (again compared to the very first design) and will be set up based on our experiments with the final boxes.
4. If we put everything into one chassis like usual (instead of 2 monoblocks) we can use 1+1 remaining half of the 2 ECC99 tubes for something else - thinking about a separate headphone circuit now.. not sure yet.
Am pretty sure way back in the day when the 859 appeared as a DIY project there was no copyright assigned to the schematic, best check! but if you build for non commercial use and don't send it the the states for a buddy to listen to you hopefully will be ok .
The schematic can be improved and changed from its starting point anyway, nothing stays the same !
The schematic can be improved and changed from its starting point anyway, nothing stays the same !
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