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In Reply to: RE: 38H OPT for 845, so so? posted by walge on April 10, 2021 at 03:09:16
There is not anything better to do measurments at or near maximum power, it's just an academic measurement wich gives no information about what is better.
A performance measurement at normal listening levels gives me more information. I am not interested in how much heat is generated at low or high frequencies at maximum power although this can be calculated if needed.
So how do you solve the bias current problem in your set-up to measure a SE transformer?
Follow Ups:
I must measure all parameters from minimum to maximum.
If I spend money or I ask to have a custom trafo I need to know all specs.
Where is the problem?
I show you the simplest way to do this.
If you don't consider a trafo as a bi-directional device we are loosing time.
Of course, a minumum of equipment you must have, but a good ss amp+scope+tester+audiocard+sw and a attenuator you can read anything
I have some measurement in AI and AP extension to convert, you will read some other things
I will prepare a specifc thread on this method.
Walter
In your opinion it's the easiest way. I simply not agree with that and i explained why.
This minimum equipement you describe are or to minimum or a lot more difficult then you say it is. Btw an Audio-Precision is way out of budget for most people €15k?
That's why you are the only person who dos this and everybody else use a different way.
But no hard feelings, if you like your set-up its fine for me. Just fix the bias problem and maybe somebody else will use it too for his 300b transformer test.
My point of view is based on electronic.
If you are agree that a trafo is a bi-directional device you can agree with my test set.
You didn't explained why this test set is not correct, you have shown a test with a signal trafo that is a differente beast mainly for the signal threated.
That's all.
To be precise I have two Audio Precision, Sys one and Sys Two
But I never spoken about AP to do the test, I spoke about a good sound card with proper setting.
Regarding bias current, be patient! :)
Walter
First of all, I never said that a transformer is not bidirectional. That is only in your mind.
So you can test both ways BUT your method is just an alternative way to test, not better, not easier. It also has shortcomings.
For SE you must have a bias current, if you make measurements at high, higher volumes you will even make the wrong measurements if you do not have the correct bias current.
With a sound card the options are quite limited. Decent frequency measurements are only possible on a modest scale. For someone like me who wants a really good transformer it is unsuitable.
For simple and good equipment i prefer a Analog discovery 2
https://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/
To be precise
I wrote more than one time that the trafo are bi-directional device without any comment by you.
Then, I wrote that, in my opinion, the test set I propose is the best to check in deep the OT trafo.
If it is possible to have a proper generator with variable Zsource and a range from 10 volt to 200 vrms from 1 Hz to 200khz ( as example) the standard method is also fine.
But the costs are very high and I don't think there is something available
For bias, I say again, please wait other info. Something interesting. I hope.
I repeat again, a good sound card and ARTA ( for example) says a lot of things about OT.
And not related to freq. response but mainly on THD vs frequency. That is the most important parameter.
The link you sent show a reasonable level equipment with some limitation ( of course, due the price)
I was not interested in your "bidirectional" question. This is common knowledge and not worth paying so much attention to.If you want a thorough check of your OT, there are better ways to do it. A large signal is not very interesting information. The ear is not very sensitive to high sound levels, instead low level performance is much more interesting. We can also see the benefits of better core material when looking at lower levels. So no, I don't need a generator 10V - 200Vrms.
I am also curious if you could measure a transformer like this picture above with ARTA or the AP????
Edits: 04/10/21
I forgot.
If you aren't interested on bi-directional question is not a problem for me, of course.
The fact that you don't answer is clear for me.
Then, your opinion on large signal is opinable and not correct under the technical aspect; what do you want forma an OT trafo? to get 1 mV?
Then , regarding your test, please let me know the brand of your trafo and I will buy it for test; I have a good number of trafo tested left in a corner. I have also company that make for me the stuff on request ( the ones in the photo)
Last, of course the AP will test at the best the stuff and it is reference test set; surely your test set is not at the same level.
With Arta and sound card, as wrote more tha one time, you can understand lot of things.
Walter
Actually, this rejected transformer causes problems in a tube circuit.
And the real answer is no, we couldn't find the problem if we used an AP or ARTA because of their bandwidth limitations. Fine equipment in itself but good at other things.
But for that problem we could have used a scope and some other skills. Just out of curiosity I made a frequency curve.
This is a SE transformer 3500 Ohm tested with a EL34 in triode mode. Kathode bias and the low frequencie is a bit limited by the electrolitic capacitor.Would be nice to have a 10dB NF and see what happens, 3Hz -300kHz must be possible for SE. With a 300B even slighty better.
Edits: 04/11/21 04/11/21
Please decribe the test set up.
will buy this trafo for my test, please send details.
PS= it is funny, you show a diagram of one trafo seems to be fine but, then after my request to buy it, you wrote that this one got problem in a circuit.
It is a joke?
Something strange.
I repeat I am ready to buy your OT, to verify with a certified test set.
Walter
Walter,That was just a example of a transformer ( pp 5k) and what could be wrong and what happens if the test equipment has limitations. That perticular transformer i don't have anymore, it went in the trash bin.
The latest picture i posted of the 3500 Ohm SE i can make but not for sale, as we all know, i don't sell here anything. So don't send pm.My test equipment is good enough, the "certified" (what ever that means) test set would not make any differance.
Edits: 04/11/21
Ok, I understand.
At the end of the story you can't give any addtional specs or photo on the stuff you mentioned.
It seems a virtual world.
If I have the OT like you description I will be in hurry to sell them!!!!!
In attach the photo of two OT for SE, on the left is the one custome made from F.I.A.T. Roma for me, it is double C, 0,01mm, with a classical bell, for 300B s.e. Involved in a circuit the performance are good and the sound very fine.
The other is the one I spoke before, comes from Onori always in Italy, amourphos, 0,023 mm.
As you see I show the stuff I am speaking, this make a great difference.
Last, the AUdioreview magazine is insithe EISA so the test set is compliant with worlwide dierection.
Bye
Walter
Ohh, you like pictures of my projects?
The differance between you and me is that I actually design transformers.
Edits: 04/11/21 04/11/21 04/11/21 04/11/21 04/11/21
Good!
It is possible to buy or not?
not allowed here Walter
Ok
If not here
Where?
Just friends.....
I will repeat again.
On OT trafo you don't reach that type of answer. I mean only trafo not involved on a circuit
And please explain which type of signal you are using and the circuit; for a 2,7 volt on 8 ohm, 1 watt, with a ratio of 27 (in your case) you need 67,5 volt rms on primary. This is an acceptable start point
In addition a practical example of performance.
In photo a pair of monos built by me years ago, double p-p pf 300B
Then the response with and w/o FB (10 dB)
As you see w/o FB the answer is fine and wide
Then a CCL test, where I sent by AP some signal to reach the max power changin the load.
Normally with a poor configuration the curve tends to be horizontal because the quality of OT and the proper configuration.
In this case the magnetic circuit is big and the configuraion of OT is little bit different, single secondary at set at 5 ohm. (this is another aspect of the test set I use)
Lowering the load the power tend to increase ( with a good ss normally the curve is more vertical) and this is fine.
Of course the signal are continuos and impulsive.
Due to the huge Power bank the lines are similar; normally with poor capacitance ( less Joule) the curve are dissimilar, the impulsive is better, of course.
Walter
Really well done! I love seeing the power tubes up front. I'm surprised you didn't need to shield the small-signal stages.
--------------------------
Buy Chinese. Bury freedom.
Thanks
I have done some stuff also with different tubes as KT120 and KT150, same aesthetic.
The driver stage ia ECC88 + 6H30; very strong and very linear.
The amps are quite also with 300B with the filaments in ac.
The OT are custma with songle secondary set at 5 ohm
Walter
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