ecl82 class A pp, need schematic

[artosalo]

Power toroidals have been measured to have over a 100 Henries of primary inductance...

I just measured the primary inductance of my 100 VA / 230 V / 10 V power toroid. The result was quite far from the above, only 2.5 H.

After getting that result I begun to wonder why power transformer manufacturers would make transformers with 100 H primary inductance, when 2.5 H would be sufficient. Why would they spend that much copper in vain ?

Has anybody else measured such high (100 H) primary inductances from power toroids ?

 

[Shoog]

Steve Bench has a nice write up on this on his site and that is where the measurement was derived from.

Shoog

 

[artosalo]

Link ?

 

[GoatGuy]

Artosalo,

I see how 2.5 H could be the right value. (This is an edited comment, where formerly I thought H should be about 85 or so)
Also, I can see how 1.4 H would be the right value.

Did a little fast'n'dirty piecewise integration using Newton's method. Peak amps are right where they're supposed to be for a 100 VA, 230 V transformer, when primary winding = 1.4 H


GoatGuy

 

[Shoog]

Do a search for Steve Benchs website, its been over 5 years since I was last there so its as easy for you to find as myself.

Shoog

 

[artosalo]

I visited Steve Benchs website, but there is too much information to search for that particular item.

I think it is one of those many legends here, that power toroids with 100 H would exist. If it existed, it were a sign of unskilled design.

 

[Shoog]

I visited Steve Benchs website, but there is too much information to search for that particular item.

I think it is one of those many legends here, that power toroids with 100 H would exist. If it existed, it were a sign of unskilled design.

The point overall is that they work, they sustain signals down to a level comparable to many EI, lots of people have used them successfully. You should lash up a simple design and try it for yourself. I fairly much guarantee that you will be surprised.

Shoog

 

[artosalo]

I know how an OPT with 2.5 H primary impedance works and behaves.
With typical output tubes the bass end will be attenuated but can be fixed a bit with GNFB.
With low impedance tubes the case is better, but still the THD is considerable at bass frequencies.
This in turn may be experience as some kind of "synthetic bass" in practice giving illusion of "strong" or "deep" bass but actually is distorted bass.
I well can believe that some DIYers can enjoy about such.

 

[Shoog]

You obviously didn't try very hard to find the reference;

I also did some investigation of the Amveco toroidal power transformers on the Owens Inductance Bridge (as described on these pages. I found those transformers had high primary inductance (on the order of 100Hy) with low leakage inductance (on the order of 100uHy). That implied that they *might* be good for audio. As it turns out, they work quite well, are inexpensive, and perform quite adequately.

Shoog

 

[artosalo]

Link ?

 

[Shoog]

Now you are been lazy aren't you.

Of AC/DC Amps, Toroid Transformers and Small Size

I can't see how you failed to find that since it is clearly indicated on the index page.
I guarantee that Steve Bench is a better engineer than either you or I, so I will take his word for it - and the testimony of my own ears.

Shoog

 

[artosalo]

Now you are been lazy aren't you.

Maybe, but if you had this information, why did you not give the link at once ??

I guarantee that Steve Bench is a better engineer than either you or I, so I will take his word for it - and the testimony of my own ears.

I did not know the we so close that you can classify my knowledge.

But tell me how you use ears to measure inductances up to 100 H. I don't know anybody so skilled person.
You my be a real superman.

 

[Shoog]

Maybe, but if you had this information, why did you not give the link at once ??



I did not know the we so close that you can classify my knowledge.

But tell me how you use ears to measure inductances up to 100 H. I don't know anybody so skilled person.
You my be a real superman.

I didn't have that link when you asked me - you went to the site and failed to find the reference which was within the first page - clear as day.

The point is - you claim that the bass should sound a particular way, it doesn't. That is the proof of my ears and that is good enough for me. The fact that Steve Bench actually measured the inductance was what gave me the confidence to see if they would work. They did and I find it a little odd that people would dismiss it without first trying it themselves.

What is most important in the context of this thread is that the thread starter explicitly stated he wanted to try it and find out for himself - and I shared my personal experience that it could work very well. However, to qualify - the ECL82 is not an ideal match since it requires a quite high primary impedance which is hard to achieve with suitable toroidals - though not impossibly so.

Shoog

 

[artosalo]

The point is - you claim that the bass should sound a particular way, it doesn't. That is the proof of my ears and that is good enough for me.

Actually I said that distorted bass (that is created by too low primary inductance) can give the illusion (=sound like) of "strong" or "deep" bass.
But you said it does not. So does it sound bad ? I thought that it sounds good !

The fact that Steve Bench actually measured the inductance was what gave me the confidence to see if they would work.

There must be some systematic mistake with those test results.
100 H as a primary inductance of any power toroid is illogical, because only 1 to 2 % of that inductance is sufficient. No manufacturer would spend huge amount of material and effort to gain nothing.

Also the leakage inductance Bench measured - 100 μH - is practically impossible, if the primary inductance were 100 H. Any engineer will understand this.

As a reference I just measured these values from my power toroids I have now in hand. I tested six (6) different toroids ranging from 40 VA to 300 VA.
The primary inductance varied from 1,5 H to 8,2 H and leakage inductance from 2,0 mH to 15,5 mH. I can list the types I tested with detailed results, but I think that will give no more value to this discussion.

What is most important in the context of this thread is that the thread starter explicitly stated he wanted to try it and find out for himself - and I shared my personal experience that it could work very well. However, to qualify - the ECL82 is not an ideal match since it requires a quite high primary impedance which is hard to achieve with suitable toroidals - though not impossibly so.

I agree. Only tubes with very low Rp can give good results (with GNFB).