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Old 26th March 2007, 06:17 AM   #1
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Unhappy PT winding calculations HELP

Hi, (You can skip the first 3 paragraphs!)

The major obstacle In planning any of my projects is the complete unavailability of PT's & OT's here in egypt. -for OTs I'll eventually start another thread-

I have tried to custom wind a PT at a pro transformer winder, but the only proffesional thing about him is that he makes a living out of it! The PT was a mess.

Importing transformers to egypt, is very difficult for many reasons so I decided to wind them myself. I bought an old winding machine & have been practicing with fishing line and old wire and I'm improving.

To learn the necessary calculations I have consulted "The Radiotron Designers Handbook" Chapter 5, section 5

From what I understood I made the attached calculation sheet with the points I dont understand in red.

My Questions are:

1- How do I find out the DC output voltage of a certain schematic?
And would the AC high tension voltage shown on some schematics (for instance 350-0-350)be of any use in the calculations? How?
Claus Byrith design as an example

2- How do I know the DC output current of a certain schematic?

3- How do I determine the rectifier & filter loss?

4-Isnt the equations -marked in red in my sheet- on page 235 & 238 contradicting?

I really need your help
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Old 26th March 2007, 06:40 AM   #2
BudP is offline BudP  United States
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First goggle Duncan amps and down load his free PSUD2 power supply simulation software. This will , after a short learning curve provide you with a tool that will allow you to modify the transformer parameters and all of the other power supply components to arrive at the DC voltage and current you want for the amp. Do note that every time you edit the transformer specs it returns to a generic design so keep seperate notes on what you enter here. Once you have something close to what you want I can help you with the design and safety considerations.

Please go about this in an orderly process, these things are deadly and you MUST get them designed and built properly.

When you get to the OPT I can help there too.

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Old 26th March 2007, 06:45 AM   #3
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Thanx for your reply Bud, I'll do that now & Thanx for offering your help, I'll sure need it.

[ QUOTE]to modify the transformer parameters and all of the other power supply components to arrive at the DC voltage and current you want for the amp[/QUOTE]

My problem -you see- is that I cant figure out the DC current for a given schematic, the B+ voltages are always mentioned but not the DC voltage required from the transformer after rectification.

However the DC current is not stated.

I'm a complete novice so I hope I'm not getting this all wrong.
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Old 27th March 2007, 01:06 AM   #4
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Once you figured out the voltage and current requirements for your circuit. Post back on the forum.

I can guide you from there on which trans size you need to use and the number of turns to make your power transformer. All the data you need

I should be able to guide you thru once you have all of your data
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Old 27th March 2007, 01:48 AM   #5
BudP is offline BudP  United States
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Unfortunately you will have to model every power using component in your circuit separately, to arrive at a total power draw. The B+ is a DC voltage and you will have a TBD amount of B+ DC current also flowing. This is a straight forward ohms law event and the resistance you derive from it will be the final resistor at the end of the PSUD 2 sim circuit.

Once you have all of the power eating circuits modeled individually it is a straight addition of DC values to come up with the total current needed from the power transformer.

In many instances the driver tube DC voltages are just resistor step downs off of the main B+ DC supply. In others, separate windings are used and in still others completely separate transformers are used.

Then you need to also plan on the AC filament power that will be supplied and whether or not the B+ transformer should supply this too.

However, you as the amp designer must decide just how much current will be allowed to flow in the differing tube power supply circuits and since this has ramifications for the entire amplifier performance you MUST also have this design choice interaction information available to you. I suggest that you post your desired schematic, in another thread and ask for help from the circuit mavens that infest this site. Keep in mind that there are two circuits involved in each stage of an amplifier. The power circuit and the signal circuit. Sometimes, decisions you make in one circuit have a profound influence on the other and you must understand these interactions and their consequences

After all of this trying activity Nick and I can have a contest to see who can help you the most, just like the circuit mavens will have. I too design transformers as my profession.

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Old 27th March 2007, 07:49 AM   #6
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first of all I dont know how to thank you for your kindness.

It seems that it all depends on the ability to analyse the circuit to find -as Bud said- the total power draw and voltage required.


Although I have studied DC circuits many times, I can only use Ohm's law on simple theoretical circuits and cant apply it to complex ones.

I dont know the effect of capacitors on voltage & current so that also stands as an obstacle.

A friend of mine is going to introduce me to an electrical engineer who'll hopefully try and teach me how to do it.


Can we use the Eico HF-20 as an example? On the schematic the current at the PS is 105ma. and the DC voltage (if i'm correct because I dont know the effect of the 40uF capacitor) is 470V

I calculated the PT using the RDHB method using these figures, then I used Silvio Klaic's transformer calculator for the 370VAC transformer and got different results.

I'll do as you advised & let you know what happens.

Please keep this thread going, you cant immagine how much I'm frustrated because of PT & OT obstacle.

By the way my fishing line winding skill is unbelievably improving.


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Old 27th March 2007, 04:41 PM   #7
kevinkr is offline kevinkr  United States
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One of the other things that may help you is to model your proposed amplifier circuits in spice, this amongst other things will provide you with the rough current draw of the circuit you propose to build.

I strongly recommend Linear Tech's Switchercad3 aka LTSpice available free from their website.

It is quite easy to add tube models to this version of spice, although transformer modeling can be problematic (although not impossible)
I have extensive tube libraries that I can zip and email to you along with simple installation instructions. Then you have to learn to use it.

I take it that importing used items purchased on eBay is a bit of a problem? One other possibility would be to check some of the local scrap yards and see whether or not they have old military or industrial equipment with suitable power transformers.
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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Old 28th March 2007, 12:25 PM   #8
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Thanx Kevin,

I'll do just that.

I've searched at some scrap radio places & already found a Philco PT it has both 6.3V & 5V windings but I didnt measure the high tension yet.

I've asked them to collect some PT,s for me so I'll wait & see

A question off the subject, is the hammond 1645 OT suitable for the Claus Byrith 4-30? It's 30W 5K : 4,8,16 Ohms

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Old 28th March 2007, 07:29 PM   #9
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Hi Kevin,

I'm expecting the tube libraries you told me you have.

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Old 30th March 2007, 02:40 PM   #10
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Hey Kevin, did you forget me

I'm still expecting the tube libraries you told me you have.


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