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PS Transformers [message #9734]

Fri, 28 July 2006 08:55

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Do we want a very high DCR on the secondary? And how to implement tube voltage regulation in the circuit? Is that a good thing?

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Re: PS Transformers [message #9735 is a reply to message #9734]

Fri, 28 July 2006 14:32

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

No offence, but if you ask those questions on the forum, then your "designer" skills are rudimentary, both for "designing" PT and PS, especially active, tube type.
You can read various opinions, anecdotal and empirical "evidences", one-parameter "wonders", heating debates...
May I suggest a different approach? Start with the quality PT, from the people who know what they are doing (I have a good experiences with Plitron/Amplimo and AE-Europe), add a good chokes, rectifiers and caps with a little help from PSUDII, breadbord it and listen...

http://audioroundtable.com/GroupBuild/messages/1959.html

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Re: PS Transformers [message #9736 is a reply to message #9735]

Fri, 28 July 2006 16:12

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Well that would be the obvious and proper way to go about designing except how would I listen to it? I would have to build a amplifier and driver circuit then plug the PS into it and hope for the best I guess. A good learning experience except if it doesn't sound good; then a very expensive learning experience. Yet right here we have knowledgable designers who could pave the way so to speak.
Yes; of course my design skills are rudimentary; but why then do some people say use low DCR and some say High DCR on the secondaries? And one designer says you must find the off-load voltage to properly utilise the transformer. So each unit must be tested.
I have a couple PT's on hand; but not the ability to test each one for it's parameters.
So I expose my lack of design skills; can you surf? Or play golf and shoot in the low nineties? I'll play you one on one half-court, no blood no foul .

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Re: PS Transformers [message #9737 is a reply to message #9736]

Fri, 28 July 2006 17:05

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

"I have a couple PT's on hand; but not the ability to test each one for it's parameters."

What you need more? You can measure primary and secondary DCR, and with formula Rt = Rs +(Ns/Np)^2 * Rp you can find the "equivalent" PT resistance, where Rs is a DCR from CT to the one end of the secondary (from 0-350V).
For example - you measured Rp=5 Ohms, Rs=20 Ohms. Then you can measure unloaded sec. voltage, say 350-0-350 V.
Ns/Np is PT turns ratio, equal to voltage ratio (sec/prim.), say 350/117 = 3. Then our Rt = 20 + 3^2 * 5 = 65 Ohms. This Rt rectifier tube on the secondary "sees". If you don`t know current rating of your PT, then you can guess by its size, and if it is salvaged from some equipment (preamp/power amp).
You now have all you need for PSUDII - Rt, Utr - choose your rectifier and a first filter (LC or CLC), put the CCS as a load (estimated current of your amp) - and start playing with the program with various values, rectifiers, etc.
For example, you need 375V/100mA DC and you tried 10µ/10H-100R/100µ with 5R4GYB rectifier you have in your junkbox...yes, that`s about it!
Breadbording proves that you are quite close, and you liked the sound - happy end...

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Re: PS Transformers [message #9738 is a reply to message #9737]

Fri, 28 July 2006 18:16

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

I'll give it a shot; I am also following Bas DIY Mag where he has a thorough explanation of the transformer part of PSUD; similar to what you wrote; although he sounds a little less confident of the results.
He claims you must have the off-load voltage but doesn't say how to get that. He uses off-load voltage /wall voltage to get the turns ratio. You use Ns/Np; is there a difference?

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Re: PS Transformers [message #9739 is a reply to message #9738]

Fri, 28 July 2006 23:45

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

Huh, MB...you didn`t pay attention - turns ratio (Ns/Np) is equal to the voltage ratio (Us/Up)...you must measure both voltages (117V i 350V in our example).
Be VERY carefull with those voltages - potentially lethal, better leave this over to the qualified person if you are not sure about measuring and building with HV...

http://www.plyrics.com/lyrics/ramones/gimmegimmeshocktreatment.html

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Re: PS Transformers [message #9740 is a reply to message #9739]

Sat, 29 July 2006 06:58

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

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Re: PS Transformers [message #9741 is a reply to message #9739]

Sat, 29 July 2006 06:59

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Sorry; I assumed you were using the rated spec of the transformer and wall voltage. To measure off-load voltage you connect the primaries to the AC line input then use a voltmeter on the two legs of the secondaries right? But if you measure the voltages then why do you need the turns ratio? Thats already given by the primary and secondary voltage measurements.

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Re: PS Transformers [message #9742 is a reply to message #9741]

Sat, 29 July 2006 09:52

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

Well, the formulae is expressed with turns ratio - the number of turns (Np and Ns) are unchanging constant, both in ideal and real transformer.
In ideal PT, turns ratio (Ns/Np) is equal to the voltage ratio (Us/Up); the real transformer is a little more complicated. But, for our purposes (usually we don`t know Np and Ns), measured "off-load" voltages and their ratio (Us/Up) is equal to the turns ratio.
Note that "step-up" transformation "adds" Rp to the secondary multiplied with square of the turns ratio - with higher Us (and higher voltage/turns ratio) Rt is purely dominated by Rp and not with Rs! For example, we have 550-0-550V PT needed for LC supply (and "targeted" 430V DC)... say, our Rs is only 5 Ohms...but we must add (Us/Up)^2 * Rp, and (550/117)^2*Rp = 22*Rp.
It means that every Ohm of the primary DCR is 22 Ohms "transformed" to the secondary side.

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Re: PS Transformers [message #9743 is a reply to message #9742]

Sun, 30 July 2006 18:06

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Thanks D; you are doing good work here. Now I have a question; what is source impedance? I know it has something to do with the fact that Kirchners Law says that a loop must equalise at all points; but can you explain it in simpler terms? I know the words; it's the reactance looking back into the source; but I don't grasp it intuitively.

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