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Old 5th July 2007, 10:36 AM   #1
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Default Power Supply Design

Hi,
I've searched and searched but, I can't seem to find basic equations on how to design, what should be, a relatively simple power supply. I either get too many "unecessary" equations or I read "how to's" with missing parts.
I've tried using PSUII but can seem to get the voltages I need.
What I'm hoping you all could help me with are the equations to get two voltages, 250v & 180v
I have a 300-0-300 hammond transformer and was thinking of going with a full wave rectified circuit (solidstate) and for cost purposes a RC circuit.
I guess my real question is how do you calulate those different "branch" voltages I see in so many PS circuits?

I not looking for perfection more like, if they had a "tube power supply desing for dummies" i'd probably buy it.
The boozhound lab had one that was reeeally simple but it used a tube rectifier and a 275v x-former.

Many Thanks!
-Brett
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Old 5th July 2007, 10:58 AM   #2
Stixx is offline Stixx  Germany
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Brett,

I'd definitely recommend to gave another go at PSUD2 since it is the easiest and most accurate way to calculate almost any psu.
Just take your time to play around...it ain't that difficult!
With the numbers you mentioned it should be pretty easy to come up with a suitable design...

Good luck,
Oliver
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Old 5th July 2007, 12:14 PM   #3
corne is offline corne  Netherlands
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Brett,

To design the PSU you'll have to know what the load current is, and the DC resistance on the 300V-0-300V.

Try this with PSUDII
Full wave rectifier 300V and 75ohm DC resistance
C1=2uf
L1=10H, 200ohm
C2=50uF
L2=10H, 200ohm
C3=50uF
R1=2.5k

This will give you a starting point to get 250V @ 100mA out of your power transformer.
To get 180V use a series resistor from the 250V The resistor value (250-180)/Iload, Iload being the load on the 180V.
This type of PSU has a relative high internal resistance, this means the voltage will go up if load decreases. The main voltage-tuning element are C1 and L1.

Corne
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Old 5th July 2007, 02:11 PM   #4
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Just a thought - you do need to allow time in PSUD2 (i.e. a delay) for the caps to charge up. Also, be careful to specify the DCR of the power transformer correctly.
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Old 5th July 2007, 10:58 PM   #5
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Location: Monroe Township, NJ
Default Re: Power Supply Design

Quote:
Originally posted by Defbrett
Hi,
I've searched and searched but, I can't seem to find basic equations on how to design, what should be, a relatively simple power supply. I either get too many "unecessary" equations or I read "how to's" with missing parts.
I've tried using PSUII but can seem to get the voltages I need.
What I'm hoping you all could help me with are the equations to get two voltages, 250v & 180v
I have a 300-0-300 hammond transformer and was thinking of going with a full wave rectified circuit (solidstate) and for cost purposes a RC circuit.
I guess my real question is how do you calulate those different "branch" voltages I see in so many PS circuits?

I not looking for perfection more like, if they had a "tube power supply desing for dummies" i'd probably buy it.
The boozhound lab had one that was reeeally simple but it used a tube rectifier and a 275v x-former.

Many Thanks!
-Brett

Brett,

You might be "penny wise and pound foolish". You are going to need high wattage in the dropping resistor(s), if you cap. I/P filter. That's an expense. Also, LOTS of waste heat will be generated. How do you propose to deal with the heat?

If you rectify the 300-0-300 with a 5AR4 and choke I/P filter, the rail voltage should come in CLOSE to the 250 V. you want. A critical current of approx. 25 mA. is needed, if the 1st inductor is 10 H. I'm guessing your signal tubes draw more than that. The slow starting 5AR4 allows you to forego a heat generating bleeder resistor across the 1st filter cap., if my guess is correct.
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Eli D.
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Old 6th July 2007, 03:20 AM   #6
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Ray moth, you're right that does help. I had it set for a second -I always figured that was a "long" time in electronics.

Corne, Thanks! that's a good starting point.

A few key terms I read here:
ILoad, does that equal the maxium load line current I selected? For instance for my 12AX7 i selected a 2ma/180v load line so, does that make ILoad(max) 2mA??
and for my EL84 I chose a 50mA/5K (x-former) loadline.

Then, to throw a curveball in there I wanted to make it a dual SE...ya i'm nuts.
If I had to, i'd just copy some other design as i've read Morgan Jones "Valve Amplifiers" and the "Tube amp book" over and over again but, this is a class project so I have to show/document most of my calculations. The amplifier seemed no problem, this power supply is driving me nuts though.
Appreciate all the help! You all are great!

I'll keep toying with PSUII and see what happens.
-Brett
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Old 6th July 2007, 07:37 AM   #7
corne is offline corne  Netherlands
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Brett,

The Iload for 180V is the DC current in the 12AX7 in your case 2mA. If there's a signal on the 12AX7 the current will vary but the average value remains 2mA. If the EL84 is SE and therefore class A the story is the same so Iload on 250V is 50mA. Because the 180V is made from the 180V the total current on the 250V is 54mA.
For a stereo amp the current must be 108mA

I missed you wanted to use RC filtering in your PSU.
So the PSUDII set-up is:
Full wave rectifier 300V and 75ohm DC resistance
C1=50uF
R1=1100ohm
C2=50uf
R2=2314ohm (108mA @ 250V)

R1 dissipates 0.108*0.108*1100= 12.8Watts so you'll need at least a 15W resistor.
R2 simulates the required load.

The drop resistor to the 12AX7 power supply is (250-180)/(2*2mA)=17.5k.
You'll also need an extra 50uF capacitor for the 180V.

Corne
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Old 8th July 2007, 04:02 AM   #8
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thanks again!
So here is what I was able to come up with but, I'm going off the assumtion that the voltages i need will come from (C2) and (C3). Do I go by (C2) and (C3) voltages or the (L1) and (L2) voltages?
I attached a screen shot of my configuration.
Anyone know where I can get these chokes or can you recommend a place that will customer wind them??

It looks like so far this is what will work for me IF i'm reading the voltage correct from PSUD2
Full wave rectifier 300V and 75ohm DC resistance
CLC LC
C1=2uf
L1=2H 800ohms
C2=50uf
15H 1K
C3=50uf
RL=2.5k

Or

CLC RC
C1=2uf
L1=2H 800ohms
C2=50uf
R1=900 ohms 1/2watt?
C3-50uf
RL=2.5k
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Old 8th July 2007, 01:58 PM   #9
Klimon is offline Klimon  Belgium
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Quote:
Anyone know where I can get these chokes or can you recommend a place that will customer wind them??
You won't find them anywhere and I don't see why you should; a much cheaper and more flexible method with better ripple suppression would be to use a 'regular' choke, say 10H / 200ohms (not critical) and put an additional RC network before the first B+. Playing with the value of the resistor allows you to dial in the right voltage. Playing with the input cap value does the same. You can split up the additional RC-network into dual mono for better channel separation if you're using a single power supply. For driver stage B+ just add one RC stage (or one for each leg of the stereo PS), no need for a choke there.

Simon
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Old 3rd August 2007, 05:45 AM   #10
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::update::
So i've since been able to design a power supply and i'm now just finishing up wiring it all together. So, I apply my load resistance turned on my PS and much to my dismay there is NO secondary voltage coming from the (brand new) Hammond x-former (372JX). I though at first it was my solid state relay but no, i decided to just take the mains line and connect it (through a fuse of course) directly to the x-former primaries.
According to Hammond its Blue/Black to 120v and Brown/White to 0v.
So after doing this I still don't get any secondary voltage! (300-0-300)

What gives??? A DOA x-former?? Help!
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