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Old 26th August 2008, 04:09 PM   #1
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Default Darling power supply calculations

Howdy. I am building a Darling using the classic 8532/1626 layout. I want to use independent cathode resistors and all that.

For the power supply, I pucked up a a cheap ebay trans, that was originally used for a cheapo guitar amp I think. It has a 6V and a 12V winding of a couple amps each, as well as a 240 volt output.

Most of the Darling schematics (OK, the original) spec a 190-0-190 PT. Can someone walk me thru the design of a 265V B+ rail from a 240V single winding?

If the voltage is too high, could I use a tube rectifier rather than burning a bunch of power dopping it thru a resistor? I was thinking a 6AX5.

Thanks,

Robert, Mannheim
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Old 26th August 2008, 05:25 PM   #2
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The best rectifier when you work with tubes is a Tube rectifier.
From single 240 VAC You'll get about theoretically 336Vdc on capacitors after rectifier without load.
So to drop this voltage you will need neon lamps or serial zeners and resistors.
BTW how much current is needed for this rail 190v B+.
If a high current for example more of 0.5 Amperes, then better to use other transformer adjusted to give a couple of volts more than 190 V after rectifications
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Old 26th August 2008, 05:38 PM   #3
Stixx is offline Stixx  Germany
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Quote:
Can someone walk me thru the design of a 265V B+ rail from a 240V single winding?
I could probably walk you through designing a suitable psu for your "darling"...
but much more rewarding is doing that yourself...not being obnoxious here, but
download PSUD2 from duncanamps and start plugging in your parts values...
probably the diy tool with the highest fun factor

When more questions arise there will for sure be someone around here to help you out!

Viel Spass,
Oliver
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Old 26th August 2008, 09:10 PM   #4
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Default Thanks for the responses, but...

I should have been more specific. The transformer specs for the Darling from Bob Danielak are a 190-0-190 transformer, which is rectified and filtered to 265VDC to the tubes.

Therefore if 240VAC rectified is 338VDC, (240 x 1.41) then I have to drop about 70V thru the filtering to get down to 265VDC for B+ for the Darling.

Stixx: Thanks for the suggestion on the designer software. I figured that would bbe the first or second answer, and you were more than kind enough to give more than just a URL or singl sentence answer. Thanks for that. My problem with the tool is that I haven't a clue how to use it, which is really what I want the walk thru for. I learn fast, but there is no basis of knowledge for me to follow to learn from. If I was replicating something and just tweaking values, then I could likely do it. But I have a somewhat known transformer, and some chokes and the lot laying about, and I don't know where to start.

Of course I could buy a Hammond 369 and start with 190-0-190 to begin with, but that would not be as much fun (yikes...) and I already have the power supply at less than 1/2 the price. SO it behooves me to learn how to use the PS software, but I don't know where to begin. If someone could lend a hand, I would be mighty appreciative. Teaching a man to fish and all that.

Thanks,

Robert,
Mannheim.
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Old 26th August 2008, 09:10 PM   #5
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Default Whoops, I meant 260VAC from the tranny...

Sorry, I meant that it was a 260V secondary. Sorry for the confusion.
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Old 26th August 2008, 09:34 PM   #6
DougL is offline DougL  United States
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Sorry for the short answer, ...
A choke input PS is about .9 * Vtx
A Cap input supply is up to 1.4 * Vtx

Try PSUD a small Cap on the input 1 to 2 uf and see where that puts you.

Doug
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Old 26th August 2008, 11:22 PM   #7
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Hi!
From the transformer secondary winds 2x190V, or 190-0-190V Ac from before mentioned formula you will get 190*1.4=266VDC on the capacitor after the rectifier diodes or bridge which is O.K for the wanted 265VDC.
If you put a choke after rectifier bridge or diodes than you will get
190*0.9*1.4=239.4VDC which will be lower than wanted 265VDC.

So if you want to get 265VDC with choke than you'll need secondary tr. voltage of:265/0.9/1.4=210.317 or ~210Vac or 210-0-210VAC if you want to use a full wave rectifier with two diodes with common kathode.

I don't think that for this simple work you need any computer!!!
This is job for the hand or simple calculator, otherwise all we are going to be invalid people.
Good luck and be careful because this is not very safe voltages, BTW I've tried this voltages because I was not so careful and you will fell DC voltage right in the bones!!!, very different feeling when you touch Ac voltage of 50 HZ!!!
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Old 26th August 2008, 11:57 PM   #8
DougL is offline DougL  United States
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I'm off work now.

If you have a 190V transformer, with a full wave bridge, the voltage is going to be about 190 * 1.4 = 266 volts

if you have a 260V transformer and want 266V,
A theoretical full wave bridge choke input is 260 * .9 = 234 V

Too low

A Large cap input will approach 260 * 1.4 = 364 V which needs some element to drop the voltage.

PSUD gave me 266 V with a 260V, 33 Ohm transformer,a 1N4007 full wave bridge, a 4uF input cap a 15H 300 ohm Choke, a 220uF cap driving a 100 ma CSS. This is presented ONLY as a place to start, since I did not look up the current requirements, and used whatever choke showed up in PSUD.

With some effort, you should be able to match your current draw, voltage requirements and real world components and come up with something useful.

Hope this helps.

Doug
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Old 27th August 2008, 08:47 AM   #9
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Default Thanks for the basics!

I don't know what current draw the Darling has. How would I figure that out? Sum up the assumed loads of the 2 1626 and the 2 8532s?

I'll measure the values of the DCR of the PS and its true output voltage at home. It has a 220 and a 240 volt input, so I could play with values there.
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Old 27th August 2008, 09:39 AM   #10
Stixx is offline Stixx  Germany
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Robert,

your questions sound very familiar to me.... 'cause I had pretty much the same ones a few years ago. Then I didn't know sh... about tubes but wanted to build a tube headphone amplifier.

Well, I learned a lot since and made good use of PSUD2, so maybe I can contribute a bit of my "wisdom" (blush...).

There are so many schematics for the Darling that it's hard to find the right one, but from your numbers I assumed a current draw of about 28mA for one channel, which equals 56mA for both channels being fed from one psu (those numbers I found in one of the schematics floating on the internet).

Plugging that into PSUD and using your transformer (260V with a bit of regulation turns into ~ 273V) and a simple CLCRC layout results in the ~269V as shown in the attachment...
In used a tube rectifier since it helps you to drop a few volts, plus it looks very nice on a classic amp!
The nice part about this layout is that you can finetune your B+ by tweaking the value of either the first cap and the resistor.

269V is a tad high but in the tubeworld this is of no importance since most tubes have greater tolerances, B+ can vary by a few percent.

Since I am at work I can not spend too much time "designing" psu's but I hope I could lead you in a direction...somehow

regards,
Oliver

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