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Old 12th July 2012, 04:21 PM   #231
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why this website is maintenance mode at every time when i press the link.
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Old 14th July 2012, 09:17 AM   #232
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hi tony can u check post no 230 .
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Old 19th July 2012, 04:13 PM   #233
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hi tony,
can u check post no 229,
center leg 1.5inch ,thick is .35mm,
i need atleast 1500w transformer, (60,30,0,30,60,vac),
pls give me the specs. thanks
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Old 23rd July 2012, 04:31 AM   #234
ChrisA is offline ChrisA  United States
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I have some beginner questions. I understand the engineering. I have some formal education in that area but I'm having a hard time locating the materials. I live in the US (California)

1) Where to get the EI core laminates in small retail quantities?

2) What kind of paper or other insulations are people using between the layers? and where to get the tiny amount a hobby-builder would need.

3) What kind of varnish are people using. Is the kind intended for wood finish OK? It needs to take heat and few wood finishes are designed to even 85C. Is vacuum really needed?

4) has anyone tried using C-cores rather then EI cores. These look interesting. Silicon Steel C-Cores / Goss C-Cores for 60 Hz and 50/60 Hz Frequencies

My goal is to learn by making a few power transformers and then move to making audio transformers for tube amplifiers and studio equipment (compressors, limiters, mic preamps,...) So my question about c-cores applies to audio transformers.

It looks like maybe a c-core might have the advantage of a toroid but the ease of bobbin winding. And it appears that you can disassemble a c-core. Also I think a c-core would be easy to air gap if needed.
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Old 8th August 2012, 11:31 AM   #235
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sir tony,
this have been talk about in another thread,but i feel free to ask this matter to a master
900w @ 4 R said in need of 1800kva for stereo 900w
most cases in our country and you know it,amateur builder use big traffo as they can,
but resulting into burned output,
my question is what was the rule of thumb regarding this output and transformer balancing,
and please show some traffo computation in different impedance.
8,4,2 R
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Old 8th August 2012, 11:41 AM   #236
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
Engel,
the usually recommended transformer size is one times to two times the maximum power output of the amplifier.
For a 900W power amplifier you could use a 900VA to 1800VA transformer. For a stereo amplifier putting out a maximum of 900W+900W you could use a 1800VA to 3600VA transformer.

Your selection of a 1800VA transformer will work.

Burning out of the output stage is a completely different issue. It has nothing to do with the selection of an appropriate transformer. Reliable output stage is down to selecting/designing the output stage to meet the duty you require.
For a ClassAB stage with a target output of 900W expect to use ~3600W of mosFET output devices per channel.
I would recommend that you do not adopt a ClassAB output stage and instead adopt one of the "special" classes designed specifically for ultra high power.
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regards Andrew T.
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Old 9th August 2012, 12:40 AM   #237
AJT is offline AJT  Philippines
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Location: Palatiw, Pasig City
Quote:
Originally Posted by engel dela pena View Post
sir tony,
this have been talk about in another thread,but i feel free to ask this matter to a master
900w @ 4 R said in need of 1800kva for stereo 900w
most cases in our country and you know it,amateur builder use big traffo as they can,
but resulting into burned output,
my question is what was the rule of thumb regarding this output and transformer balancing,
and please show some traffo computation in different impedance.
8,4,2 R

if you are not doing sine wave testing and just playing music then the traffo should be enough....

my rule of thumb, get the biggest traffo that will fit in your box.....

burned output is a result of poor heatsinking at times....

having big traffo aggravates poor heatsinking, you know that in our place, builders just make do with what is available....

using smaller traffo otoh can result in burned out traffo due to over heating of the copper coils and core saturation when current demands exceeds the capabilities of the iron cores....

it is all a balancing act.....
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Old 9th August 2012, 03:50 AM   #238
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andrewt
thanks very informative
kuya tony,
most of our diy'er get alum @ deeco
you mention before there are two extrusion company here at ph,where?
have you tried this extruded alum,any picture
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Old 9th August 2012, 04:01 AM   #239
AJT is offline AJT  Philippines
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Location: Palatiw, Pasig City
still no luck with local extruders, Hooven Comalco ceased operations after Ondoy...
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Old 17th August 2012, 07:52 AM   #240
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any of you transformer guys know if this is even possible:

on P Turner's website - page PP OPT calcs Page 3 there is a small diagram/overview of a transformer and the primary and secondary are interleaved [hope that's the right word].
Is this even possible either hand winding or automated ?

After the bottom section of the primary has been laid if you then start the secondary above it and try to wind either in the same or opposite direction the primary winding below basically will tangle every which way ? Or am I missing something completely obvious ?
His diagram seems impossible.
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