C core output design

bigbulb · 12th July 2005, 04:12 PM

Hi all,

Most of calculations for output trans on WWW mostly use EI core, I wish to know if anyone of you know how to calculate the c core SE output transformer?
Normally EI core with 14 cm square of center cross section area will handle 10 Watts SE down to 25 Hz with no problem, but if we optain c core with the same cross section area, it will be 3~6 times bigger than EI core which is not quite logic. ( look at those Lundahl with small iron but perform well)
Anyone can explain this?

BigBulb

cerrem · 12th July 2005, 05:05 PM

The equations are the same for strip C-core and E-I laminations..
For the same given cross sectional AREA , you just need to see what the magnetic path length is for that core.... I don't recall there being a 3~6 times increase in size....then you refering to a larger core???
Give specific examples for clarification...such as lamination sizes and C-core sizes that you are comapring...

Chris

bigbulb · 13th July 2005, 12:32 AM

Hi,

I'm refering to the core size. For example, I have a push pull EI transformer rated 30 watts and the core cross sectional area is 11 cm square , ( 3.2 cm X 3.5 cm) using EI 96 lamination.
I have a pair of faulty double C core push pull output trans, I measured the core cross sectional area and it is only 5 cm square. ( 2.5cm X {1cm + 1cm}, double core ) This double C transformer is rated 35 Watts. If I choose double C core that have 11 cm square of cross sectional area, ( from some manufacturer's data sheet) The whole transformer size will be 3~ 6 times bigger than the actual 35 Watts double C core trans.

If I follow the calculation , 11 cm square of core size will give 30 Watts in pusshpull is about right but if I calculate the power rating for 5 cm square of cross sectional area, it only 6.5 watts for push pull,
This shows C core gives more efficient and smaller core size can give higher power rating, that's the problem, I don't know how to determine the C core power rating.
Please Help!!

Regards,
BigBulb

cerrem · 13th July 2005, 08:01 AM

OK....Now I see what the problem is...
To explain this in full detail would be very long winded...I will keep it brief...
You really can not compare the two transformers...without knowing way more data...and it has nothing to do with C-core or EI laminations...
You can not corelate wattage to the core size....some books do this, but it is really incorrect, unless you are using the same standards for both transformers....
Manufacturers, do not all use the same STANDARD for defining the power output of thier output transformers...
The designer chooses this at will...
When I rate my OPT's I rate them at 20 HZ and at flux density of 12,000 Gauss...
While another manufacturer will rate thier power output at 400HZ and at 16,000 Guass....
This will produce totally different power levels for a same size given core... The later will show a higher power output for advertising hype but at the expensive of higher core distortion...
If the core material is different , then all bets are off, but usually 95% of output use M6 material...
One company may choose to use 1200 CM/A wire gauge while another may use 600 CM/A ...thus yielding more window area, allowing more turns, thus a lower flux density, lower core distortion and better inductance...at the expense of more copper losses which makes the audio less open and less clear sounding..
ANother consideration is the plate load...the larger the plate load then the bigger the AC plate volatge produced, this a larger flux density..therefore you need more turns...BUT the larger plate load for the same Wattage will have less current, thus a smaller wire gauge is used, therefore you better fill the window...
Also...the required inductance for a given plate load for THE SAME -3dB low frequency pole will be different....so this plays a big role as well.....and what are the different magnetic path lengths for these given cores....this also affect the L.....
So..... You need to examine transformers on a case-by-case basis from top to bottom before comparing them to each other...

Chris

bigbulb · 13th July 2005, 10:32 AM

Hi,

Thanks for your info, I will experiment with those C core, and I had been told that was M5 0.30mm which is lower loss than M6.

Thanks.

Regards,
BigBulb

trancy · 14th July 2005, 07:28 AM

try this

http://www.diyaudio.8m.com/Ot/ot_en.html

lp

trens

bigbulb · 15th July 2005, 01:38 PM

Hi ,

I had read this before, I have a question regarding this page, The C core cross sectional area is f1+f2, is that true? or just only one side?

regards,
BigBulb

cerrem · 15th July 2005, 05:07 PM

If your using a double C-core...then yes, you add up the AREA from both....
To be honest, that web-page about transformers is totally messed up....that is NOT how to design a SE transformer...
There are many considerations...here is just a quick look at a few things and is in no way complete...
The first thing you need to do is figure what plate load you need, then at what DC current is your DC idle current...
Then based on the plate resistance of your valve and the expected frequency response..you calculate the needed inductance, leakage and capacitance as your target goals..
You choose a winding geometry, interleaving, that works the best.... Too many interleavings of Primary and Secondary can be bad...there is an optimum geometry...
You then choose your maximum flux density...lets say 13,000 Guass to occur at 20Hz and at full power output...
For SE output transformers... you have to deal with the sum of your DC flux density and your AC flux density..... The more turns of wire, then the more DC flux density goes up... while AC flux density goes down... for starters set transformer Flux to be split evenly between the AC and DC flux..so make each at 6500 Gauss.. ALso remember that you need to do the negative air-gap method to calculate the proper gap to get the required inductance considering the turns and core area... It's all a balancing act ......
Choose your wire gauges between 800CM/A and 1000CM/A for primary and 600-800CM/A for secondary...

Chris

bigbulb · 16th July 2005, 11:53 AM

Hi cerrem,

Thanks for your info. I had calculated a 2 watts output for my 6C45 SE amplifier, and the primary result is 6200 turn for 4Kohm primary if I use 12.5X16X40 c core, I never seen a SE transformer have so many turns for primary, 3000 turns at the most. Some says c core need more copper for that reduced iron, is that true? 6200 turns for primary is correct? or I calculate it wrong?

Regards,
BigBulb

cerrem · 16th July 2005, 06:39 PM

I can assist you with this transformer design...
I need to know EXACTLY what core you have..
Can you measure the Hieght and Width of the surface of the gap... is that the 12.5?? and the 16cm numbers ???
Is 40cm the legth of the entire two halves of the C-core when they are butted together???

What is the intended goal ?????
What would you like to make???
A headphone amp???
Do you prefer to go SE or Push-Pull???
Usually with SE amps...you want to take advantage of high voltage tubes.... Thats why transmitting tubes are popular...
The reasoning is that you want to keep the DC current low but want to produce the most WATTS..so you compensate for the low DC current by using high DC voltage...

Chris

12th July 2005, 04:12 PM	#1
bigbulb diyAudio Member Join Date: Aug 2004 Location: klamazoo	C core output design Hi all, Most of calculations for output trans on WWW mostly use EI core, I wish to know if anyone of you know how to calculate the c core SE output transformer? Normally EI core with 14 cm square of center cross section area will handle 10 Watts SE down to 25 Hz with no problem, but if we optain c core with the same cross section area, it will be 3~6 times bigger than EI core which is not quite logic. ( look at those Lundahl with small iron but perform well) Anyone can explain this? BigBulb

14th July 2005, 07:28 AM	#6
trancy diyAudio Member Join Date: Feb 2004 Location: Slovenia	try this http://www.diyaudio.8m.com/Ot/ot_en.html lp trens __________________ too much is just enough

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
what are the advantages of double core output transformers vs EI ?	bembel	Tubes / Valves	12	2nd November 2006 02:24 AM
C core output transformer	Glass_painter	Tubes / Valves	8	25th December 2005 09:21 AM
R-Core Output Trans from ICL	reinhard	Tubes / Valves	9	9th September 2002 07:28 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

12th July 2005, 05:05 PM	#2
cerrem diyAudio Member Join Date: Jun 2005 Location: San Diego, CA	The equations are the same for strip C-core and E-I laminations.. For the same given cross sectional AREA , you just need to see what the magnetic path length is for that core.... I don't recall there being a 3~6 times increase in size....then you refering to a larger core??? Give specific examples for clarification...such as lamination sizes and C-core sizes that you are comapring... Chris

13th July 2005, 12:32 AM	#3
bigbulb diyAudio Member Join Date: Aug 2004 Location: klamazoo	Hi, I'm refering to the core size. For example, I have a push pull EI transformer rated 30 watts and the core cross sectional area is 11 cm square , ( 3.2 cm X 3.5 cm) using EI 96 lamination. I have a pair of faulty double C core push pull output trans, I measured the core cross sectional area and it is only 5 cm square. ( 2.5cm X {1cm + 1cm}, double core ) This double C transformer is rated 35 Watts. If I choose double C core that have 11 cm square of cross sectional area, ( from some manufacturer's data sheet) The whole transformer size will be 3~ 6 times bigger than the actual 35 Watts double C core trans. If I follow the calculation , 11 cm square of core size will give 30 Watts in pusshpull is about right but if I calculate the power rating for 5 cm square of cross sectional area, it only 6.5 watts for push pull, This shows C core gives more efficient and smaller core size can give higher power rating, that's the problem, I don't know how to determine the C core power rating. Please Help!! Regards, BigBulb

13th July 2005, 08:01 AM	#4
cerrem diyAudio Member Join Date: Jun 2005 Location: San Diego, CA	OK....Now I see what the problem is... To explain this in full detail would be very long winded...I will keep it brief... You really can not compare the two transformers...without knowing way more data...and it has nothing to do with C-core or EI laminations... You can not corelate wattage to the core size....some books do this, but it is really incorrect, unless you are using the same standards for both transformers.... Manufacturers, do not all use the same STANDARD for defining the power output of thier output transformers... The designer chooses this at will... When I rate my OPT's I rate them at 20 HZ and at flux density of 12,000 Gauss... While another manufacturer will rate thier power output at 400HZ and at 16,000 Guass.... This will produce totally different power levels for a same size given core... The later will show a higher power output for advertising hype but at the expensive of higher core distortion... If the core material is different , then all bets are off, but usually 95% of output use M6 material... One company may choose to use 1200 CM/A wire gauge while another may use 600 CM/A ...thus yielding more window area, allowing more turns, thus a lower flux density, lower core distortion and better inductance...at the expense of more copper losses which makes the audio less open and less clear sounding.. ANother consideration is the plate load...the larger the plate load then the bigger the AC plate volatge produced, this a larger flux density..therefore you need more turns...BUT the larger plate load for the same Wattage will have less current, thus a smaller wire gauge is used, therefore you better fill the window... Also...the required inductance for a given plate load for THE SAME -3dB low frequency pole will be different....so this plays a big role as well.....and what are the different magnetic path lengths for these given cores....this also affect the L..... So..... You need to examine transformers on a case-by-case basis from top to bottom before comparing them to each other... Chris

13th July 2005, 10:32 AM	#5
bigbulb diyAudio Member Join Date: Aug 2004 Location: klamazoo	Hi, Thanks for your info, I will experiment with those C core, and I had been told that was M5 0.30mm which is lower loss than M6. Thanks. Regards, BigBulb

15th July 2005, 01:38 PM	#7
bigbulb diyAudio Member Join Date: Aug 2004 Location: klamazoo	Hi , I had read this before, I have a question regarding this page, The C core cross sectional area is f1+f2, is that true? or just only one side? regards, BigBulb

15th July 2005, 05:07 PM	#8
cerrem diyAudio Member Join Date: Jun 2005 Location: San Diego, CA	If your using a double C-core...then yes, you add up the AREA from both.... To be honest, that web-page about transformers is totally messed up....that is NOT how to design a SE transformer... There are many considerations...here is just a quick look at a few things and is in no way complete... The first thing you need to do is figure what plate load you need, then at what DC current is your DC idle current... Then based on the plate resistance of your valve and the expected frequency response..you calculate the needed inductance, leakage and capacitance as your target goals.. You choose a winding geometry, interleaving, that works the best.... Too many interleavings of Primary and Secondary can be bad...there is an optimum geometry... You then choose your maximum flux density...lets say 13,000 Guass to occur at 20Hz and at full power output... For SE output transformers... you have to deal with the sum of your DC flux density and your AC flux density..... The more turns of wire, then the more DC flux density goes up... while AC flux density goes down... for starters set transformer Flux to be split evenly between the AC and DC flux..so make each at 6500 Gauss.. ALso remember that you need to do the negative air-gap method to calculate the proper gap to get the required inductance considering the turns and core area... It's all a balancing act ...... Choose your wire gauges between 800CM/A and 1000CM/A for primary and 600-800CM/A for secondary... Chris

16th July 2005, 11:53 AM	#9
bigbulb diyAudio Member Join Date: Aug 2004 Location: klamazoo	Hi cerrem, Thanks for your info. I had calculated a 2 watts output for my 6C45 SE amplifier, and the primary result is 6200 turn for 4Kohm primary if I use 12.5X16X40 c core, I never seen a SE transformer have so many turns for primary, 3000 turns at the most. Some says c core need more copper for that reduced iron, is that true? 6200 turns for primary is correct? or I calculate it wrong? Regards, BigBulb

16th July 2005, 06:39 PM	#10
cerrem diyAudio Member Join Date: Jun 2005 Location: San Diego, CA	I can assist you with this transformer design... I need to know EXACTLY what core you have.. Can you measure the Hieght and Width of the surface of the gap... is that the 12.5?? and the 16cm numbers ??? Is 40cm the legth of the entire two halves of the C-core when they are butted together??? What is the intended goal ????? What would you like to make??? A headphone amp??? Do you prefer to go SE or Push-Pull??? Usually with SE amps...you want to take advantage of high voltage tubes.... Thats why transmitting tubes are popular... The reasoning is that you want to keep the DC current low but want to produce the most WATTS..so you compensate for the low DC current by using high DC voltage... Chris

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)