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hi guy.
i'd like to know what's your guy think about the power trannies current rating on high voltage section. i have seen some expert around here shooting for 3 to 4 time the current of the actual circuit draw ,then there is some expert highly regarded the 1% power transformer which design for the actual current draw of the circuit . say if the circuit draw 30ma then design the trasformer with 30ma no more . also i don't really understand what the heck 1% transformer really means . any comment on this ?
Cheers
Lovetube
Follow Ups:
Kind of like hauling around a fat woman when a food store exists on every city block. Bigger is not always better.
2x current with reasonably low DCR works fine. Internal shielded toroidal transformer with a Corcom AC line input filter will quickly transfer a lot of current and does not produce a large external magnetic field so toss the 30" wide chassis as well.
Lovetube,
Power transformer design is not difficult nowadays. PSUD2 is quite enough. Design your own PSU with PSUD2 and see the current peak value through the secondary (It1). This is current value for calculated thickness of the secondary wire.
Most transformer cores today come from China or India. Hard to find a precise and accurate data for these cores. Therefore we recommend to take the value of peak current through secondary (not sinus value).
Your 30 mA requires about 100 mA (C input PSU) through the PT secondary. With L input PSU, current peak wil be about 50 mA (or so).
You will see exact value after PSU design in PSUD2.
Best diying.
transformers have to be nearly obsolete surely switch mode will come into there own soon enough.
Hi,I covered this beautifully eight years ago - after about 30 years of A-Bing this on DHT amplifiers, almost always Class A1.
Boy, did I make enemies. Here goes, to remind you all:
DCR of half the high voltage secondary winding (if a center tap) or entire secondary( if a non center tap) of a typical (audio output tube) amplifier :
" HIGH FIDELITY" is 20 Ohms or less DCR.
" ULTRA HIGH FIDELITY" is 10 Ohms or less DCR.
And this hasn't changed ONE IOTA.
Cheers,
Jeff Medwin
Edits: 04/26/12
> " HIGH FIDELITY" is 20 Ohms or less DCR.
> " ULTRA HIGH FIDELITY" is 10 Ohms or less DCR.
And what is the meaning of these statements in terms of engineering? Any s/n ratio, dynamic range numbers, distortion spectrum analysis of finished products (amplifier connected to this PS), whatever?
YES JEFF, you made enemies but it will never be me.We disagree on many things but you will always be a friend.
"Boy, did I make enemies."
No, you didn't make any enemies apart, possibly, from Mr Dennis Fraker. Dennis it was who taught us all that the power transformer is an ACTIVE component of the power supply and is thus not required to be of low DCR.
Incidentally, the link you included is to a thread from 2009, specifically to a posting by a person identifying himself as "JLH", whose contributions to that thread seem to be confused, at best.
Jeff, can you please post a link to information which indicates "High Fidelity and Ultra High Fidelity" as it pertains to DCR?
Wheezer,
It was originally in about 2004 from what I can tell. Wasn't able to quickly find the original description I posted. Below is just a DCR "recap" in 2008.
Jeff Medwin
I was thinking, at the very least - Wikipedia!
Cheers
So that is the "punch line" Wheezer??? Good for you.
Sorry, you got it from the source who did all the work and all the listening, directly and hands-on, over about 30 years.
Jeff Medwin
Determine the class the amp will operate in.
Measure the class A(mA) and when/if it hits class B(mA).
Add the FE tubes with the class A total.
From there you can work some calculations on the mA size of the PT - Class A + peak, 50% to 70%.
If you go 2x, how will you hit the desired B+?
If it's a preamp typically they run Class A.
I would run the calculations, M6 lams and send it off to Jack Elliano for the build.:-(
"If you go 2x how will you hit the desired B+"
that is the exact concern and hence this questions.
Lovetube
A good winder will get the job done.
Do all the math first including choke DCR and so forth, if the rail voltage is that critical.
Jack Elliano did wonders with hitting the requested mark.
Guitar amps should be designed at current rating of transformer. Part of the sound musicians like is due to thee higher voltage drop.
Home entertainment amps should have a low DCR for plenty of current reserve attributing to good voltage regulation. PP operating in Class AB or SE are most critical. I use approximately double the current rating.
I compared transformers into a LCLC filter not exceeding 100 ohms & use a low voltage drop rectifier such as a GZ34 or damper tubes. I compared that design to a shunt regulated that is as stiff a power supply one can achieve. Guess what, I hear no difference in-between the two power supplies. I also tried huge transmitter chokes at a combined 30 ohms. Again I hear no difference. Thus I do not require 30lb 8" x 8" x 10" chokes.
Some could argue my system is not detailed enough to hear the difference in microdynamics. I would tend to disagree with that.
My limited power transformer experience has always been overkill.Antek power transformers are a bargain.
The 18lbs Haybour on my 2a3 amp is just incredible...and costs 4x as much.
I'd prefer the latter in all of my builds... but haven't given up on toroids yet. I'd like to do some experimenting to get a peek at the results of the wide band part of the equation....didn't have trouble with it with my monoblocks...but they don't even come close to the sound of my stereo 2a3 amp... I am tired of carrying the heavy fucker though. :) (its only 58 lbs, paks monoblocks weigh more than that each!)
The toroids in my monoblocks are ice cold....never even luke warm...and have moderate DCR on the secondary, I think ~ 30 ohms for most of them.
The 4TS320 (or something like that) does have a shield.
Edits: 04/26/12
IMHO, I look for test equipment transformers made for Hewlett Packard or Tektronix that have dual primaries or international specs; 120 and 240v. PAECO made many for HP. There are many parameters that have to be juggled but SIZE matters. The larger core(the cross section of the center tongue where the wire is wound around) will yield a better transformer. Another criteria that is hard to investigate is whether the core window is filled up with wire and the use of an electrostatic shield. I tend to stray away from toroids as they are wide band and will pass most any trash on the power line unless they have a shield between the primary and the secondary. You don't want the tranny to overheat or to vibrate excessively and undersize trannys will do that. You also don't want to over tighten the bolts holding the laminations together. They will deform the soft iron. Good transformers are expensive but the price will ward off any problems down the line and we all want our projects to be successful. Ray
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
I had one in a chassis and no matter what amp I built in it. It never sounded good. Always the bass sounded thin and in the end I had to trash it because of the mechanical hum. Perhaps it was worn out I don't know but the few windings it had where all pretty high dcr. I suspect that most the current in those trans are wired auto former off the mains.And most the core is for the heaters. As it turns out I have recently re coated the chassis for another go with a different tech trans to try again. This one has even less ht windings just 2 one center and one not but the dcr is still high. I still haven't made up my mind what to try but I think it will be a very low power amp in the hope I don't tax the trans to hard and if it is still crap I will throw it out and bolt a toroidal on top. Not worth the greif really.
"I tend to stray away from toroids as they are wide band and will pass most any trash on the power line unless they have a shield between the primary and the secondary."
Good sized ferrite beads on the primary side, with the wires looped a couple of times, suppress the power line crud. There are always tradeoffs. Toroids exhibit much lower stray magnetic fields than EI trafos exhibit.
Eli D.
nt
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
A quick search at Mouser turned up the link provided below.
While not inexpensive, stock # 710-74277290 caught my eye. The bore of that bead is approx. 1/2 inch. Several turns of wire can go around that bead and kibosh EMI/RFI rather well. :> D
Dig around and you'll find less costly beads. Make sure to buy only rounded or chamfered parts. You don't want sharp corners nicking the wires.
Eli D.
I use balanced 240v power line input on all my amps. Thanks Ray
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
http://www.ebay.com/itm/Qty-4-each-2-5mH-10A-EMI-Choke-JW-Miller-Coils-Filter-/220680930554?pt=BI_Circuit_Breakers_Transformers&hash=item33619bc4fa
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
I use 500VA ICT for B+ in a 3W SE stereo circuit.
10 ohms from one leg of the HT secondary to the CT.
Bigger is better.
I'm a contrarian here (one of the reasons I rarely post), so take my remarks with suitable caution.
I think that magnetic headroom is very important. That means keeping the induction low - around 10kgauss for grain0oriented silicon steel cores, maybe 8 or 9kGauss for non-oriented materials. Even lower for small-signal power transformers. The reason relates to external radiated fields which induce hum and its harmonics, and also vibration which affects all the other components on the chassis. Keeping the core in it's more linear operating range reduces these problems.
Getting the induction that low requires more turns of wire, and/or a larger core, compared to the normal economic design. Both are expensive, so such transformers are rarely available except by custom design. The best you can do easily is to insist on 50Hz rated transformers operated at 60Hz. This will get you down to 13kgauss instead of the usual 16kgauss. An alternate is to use dual voltage transformers at half their design voltage (240v primary operated at 120v), giving 6.5 to 8kgauss - kind of overkill there.
Many here advocate low resistance, which is a consequence of using a transformer rated for much higher current that you are actually using. There are two benefits - lower internal temperature (giving longer life) and better regulation (more important for Class AB and B push-pull amps). This criterion also requires larger and more costly transformers.
Paul
> > An alternate is to use dual voltage
> > transformers at half their design voltage
I never heard this and it has me intrigued.
Then the output voltage rating has to be
doubled because you need the same ratio.
Is it more efficient or less efficient?
Maybe plus or minus 10% or so?
DanL
To maintain the original design regulation (technical term for resistance, relative to the load) you must use the transformer at half the rated current, and it will produce half the rated voltage - i.e. 1/4 the power. Vdery inefficient use of materials!
For electrical efficiency, the core losses are very small. Taking efficiency as the power consumed that is not converted to heat, it is slightly more efficient due to the reduction in core loss - but the combined core and copper losses at the design voltages and currents are small even at the original design point, usually 5% to 10% of the delivered power.
Paul
I have two transformers on my new 845 design.
#1) Driver Section - 120Vac : 180Vac @ 80mA
I can use a 240Vac : 360Vac @ 500mA
#2) Output Section - 120Vac : 630Vac @ 160mA
I can use a 220Vac : 1160Vac @ 650mA
What do you think?
Overkill probably.
DanL
Nothing wrong with that, as long as your medical covers hernias! Jeff would approve of the high current rating, I approve of the high magnetic margin. If you do it, tell us what you hear - that's the bottom line for all of us!
Paul
BTW
I am using low DCR low/H chokes (1H and .6H)
but the caps are 60uFd/60uFd/180uFd Mtr Runs.
Not what Jeff proposes but I like it on PSUD.
Also will try the Tent Electronic Chokes MEC-50s
on the driver PS but will use 400V Solens -
no electrolytics for me.
DanL
I used this technique in my Raven style line stage, where I only wanted around 120 volt b+ and didn't want to drop a lot of volts. I used a small lundahl PT with the primaries stacked, the 6.6 secondaries in series to yield 6.6 for tube heaters, and used the 500 v ct secondary to yield 250 ct into a clClC supply, which gave me the b+ I wanted, runs very cool (can leave on forever and doesn't get warm).
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