Home » Audio » Thermionic Emissions » PS Transformers
Re: PS Transformers [message #9744 is a reply to message #9740] Sun, 30 July 2006 20:44 Go to previous messageGo to next message
Forty2wo is currently offline  Forty2wo
Messages: 163
Registered: May 2009
Master
It seems to me that you are falling down the wokie hole.

"Building the very best amp on the green earth on the first try"

This is the road to madness, or at least inaction. I, and… can I get a show of hands here, been there.

Let’s say for the 6AH4 amp we were discussing a while back. At a guess you need

Re: PS Transformers [message #9745 is a reply to message #9743] Mon, 31 July 2006 06:08 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
Simplest - we have two devices "chained" together, 2nd "sees" output (or source) impedance of the 1st device on its input. For example, if 2nd device is a preamp, and 1st is a pot, then preamp "sees" output resistance of the pot in series on its input. We can describe the pot as a one resistor in series, and one resistor in parallel to the source. Then output resistance of the pot is the parallel combination of those two resistors. If our pot is half-opened 10k device, then its output (or series, or source) resistance (that preamp "sees" in series with its input) is 5k//5k = 2k5.
Power suplies filters are more complicated - they have resistors, but also capacitors and inductors - they have impedance (say, frequency-dependent resistance to AC).
Formulas for output impedances of various filters (Pi-type,CLC, for example) you can find elsevere, RDH comes to my mind...
But, fortunately, large knowledge of network theory isn`t necessary for building a PS...

Re: PS Transformers [message #9746 is a reply to message #9745] Mon, 31 July 2006 17:43 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Can you relate this explanation to the "Source Impedance" of the secondary of the transformer to the input of the first filter element? Thanks. Or the primary of the OPT to the plate of the power tube? That would be helpfull.
I have a very comprehensive library of electronics reference books as well as explanations on the net from Rod Elliott and Bas and others. But you are building a data bank of explanations that can pull all this info together in a simple line of responnses that reflects well on ART. Thats why I persue this with you. If it becomes tiresome then I of course will cease and desist.
Anyone can learn but few can teach.
Wayne is a good example of speaker explanations; you do electronics.

Re: PS Transformers [message #9747 is a reply to message #9746] Tue, 01 August 2006 05:45 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
Huh, thanks - but frankly, I`d be more happy with "normal" forum talk about DIY, exchange of ideas and experiences - then some "teacher role"...
Source impedance in PS to the first capacitor - this is our Rt (secondary resistance + primary resistance "transformed" to the secondary side); plus impedance of vacuum tube recifier in series. It isn`t linear resistor, but for our purposes (with known current draw and voltage "drop" through the tube) we can simplified it with series resistor of typical value, say 100-300 Ohms (depends of the diode).
About tube/OPT loading I wrote many times, for example:

http://audioroundtable.com/GroupBuild/messages/1111.html
http://audioroundtable.com/GroupBuild/messages/1113.html
http://audioroundtable.com/Tubes/messages/665.html

Re: PS Transformers [message #9748 is a reply to message #9747] Tue, 01 August 2006 08:50 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Thats good. You cleared that up for me and thanks. I hope we get some DIY talk on here soon.

Re: PS Transformers [message #9749 is a reply to message #9744] Tue, 01 August 2006 09:23 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Very true; the project that gets built is more beautifull and sounds better than the perfect amp that doesn't. I fully appreciate what you're saying; but let me shplain a little. I have lots of projects going; I just finished my tube rec. EL 84 amp and re-built my Eico ST 40 which I happen to love the sound of. So you know I am not just pulling the chain here. But I decided on the 6Ah4 just as an example of a SE amp so I could use that as a platform for attempting to understand proper design and parts use. So just to get it built would'nt really do that for me. I know it is not going to be a slam dunk amp; if it helps me to understand some things then it did it's job.
You know you and Damir and Doug do good work here as I am sure you all could migrate over to the Joelist or some other forum where they know their shit and it would probably be a lot more interesting for you all. So as a heads up; this beginners stuff is a lot of help to ....me at least; I don't know if others use it. But here's my thanks.
You have brought up a good point regarding why most amps look alike. I have wondered and asked that in the past. What is the point of all this deep thinking then if the work has already been done?

Re: PS Transformers [message #9750 is a reply to message #9749] Wed, 02 August 2006 22:22 Go to previous messageGo to next message
Forty2wo is currently offline  Forty2wo
Messages: 163
Registered: May 2009
Master
When I composed that message, I meant to change the title to "On hand is good". I forgot. Without it, it changes the tone of the post. It was meant as a "use what you got" rather than "Just get on with it"

Over at AA there was a long discussion on the merits of low DSR chokes, that moved on to power transformers. At first I thought the thread had promise. Well silly me.
Also it has been very hot here and with little or no AC. Perhaps I am a bit cranky.(No miserable little smile face)

So. After your very considered reply, I reread the thread. To go back to your original question, low verses high DSR. I can not think of a reason that you would want a high DSR secondary in a SE amp.

Does this mean that that the transformer with the lowest possible DSR is always the best? Good question. I have not looked at it in those terms,

Two points. First, remember, a transformer can be drawn ‘as a black box that is full of compromises’ (I rather like that one;)
Second, if you go and order ten different EI transformers with the same spec. you will end up with a collection that weighs in at say, 5lb to maybe 12lb or more and cost < $50 to maybe several hundred. Can the "goodness" be measured in DSR alone? Probably not but it may well be an indicator. Make a good green belt project for someone. .

There is much more to say on this. Such as OK John get to the point and how do you choose a power transformer.(Hint I look in my junk box first).But it still much too hot and I am starting to fade away. More later…John



Re: PS Transformers [message #9751 is a reply to message #9750] Thu, 03 August 2006 09:51 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Please; I understood where you are coming from in the post and appreciate it. I saw nothing to indicate anything but a helpfull tone. And as I said you are right on the money regarding that advice. In fact I believe I might have indicated I had a used trans I was considering so your point is well taken.
So; I must forget the effect DSR has on the filter and concentrate on measuring what I have and computing what I can do with that? Is that a good way to put it?
Yes it is hot here too; 99 deg. We had a brownout last night and I had to spend a few hours in the bar with the wife and AC. I don't normally do that during the week much; but I should.


Re: PS Transformers [message #9754 is a reply to message #9751] Thu, 03 August 2006 21:10 Go to previous messageGo to next message
Forty2wo is currently offline  Forty2wo
Messages: 163
Registered: May 2009
Master
Oh No, don’t dismiss the question. The DSR of the transformer you end up with and how that DSR will interact with your filter are very separate questions.

My point is I do not choose a transformer on it’s DSR I find that if I choose a good transformer, low DSR usually happens.

For example, take two transformers from Hammond the 270fx Vs the 370fx. Now the 370 is set up for multiple input voltages but that is beside the point. They are rated very close 139VA for the 270 Vs 142VA for the 370. The 370 is a much beefier transformer and cost twice as much. So what’s up with that? Want to guess witch has the lower DSR?

That aside If you are trying to get close to the "rated" 150ma, which do think will run reasonably cool and not buzz like a… well you get the idea. Now if you only ask for 75-100ma the 270 may work just fine. So were dose that leave us with the DSR?

Your mission should you chose to accept it…Please let us know.;)

As to how to whatever DSR we end up with works into the filter. I need to research as well. First thoughts, model a simple filter. Say 10uf -5mh-50uf to a stepped load. vary the transformer DSR and take good notes. Maybe replace the choke with a resistor. When in doubt use 1k. I think there something on the VT52 site.
What do you say, we work this for a week or so and compare notes?…John


Re: PS Transformers [message #9755 is a reply to message #9751] Thu, 03 August 2006 21:10 Go to previous messageGo to previous message
Forty2wo is currently offline  Forty2wo
Messages: 163
Registered: May 2009
Master
Oh No, don’t dismiss the question. The DSR of the transformer you end up with and how that DSR will interact with your filter are very separate questions.

My point is I do not choose a transformer on it’s DSR I find that if I choose a good transformer, low DSR usually happens.

For example, take two transformers from Hammond the 270fx Vs the 370fx. Now the 370 is set up for multiple input voltages but that is beside the point. They are rated very close 139VA for the 270 Vs 142VA for the 370. The 370 is a much beefier transformer and cost twice as much. So what’s up with that? Want to guess witch has the lower DSR?

That aside If you are trying to get close to the "rated" 150ma, which do think will run reasonably cool and not buzz like a… well you get the idea. Now if you only ask for 75-100ma the 270 may work just fine. So were dose that leave us with the DSR?

Your mission should you chose to accept it…Please let us know.;)

As to how to whatever DSR we end up with works into the filter. I need to research as well. First thoughts, model a simple filter. Say 10uf -5mh-50uf to a stepped load. vary the transformer DSR and take good notes. Maybe replace the choke with a resistor. When in doubt use 1k. I think there something on the VT52 site.
What do you say, we work this for a week or so and compare notes?…John


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