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Old 20th January 2011, 10:20 AM   #11
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by xeclipse View Post
one channel was smoked out ...............The original outputs were a pair of 2955's & 3055's per channel with a +/-50v supply,
I would expect a +-50Vdc PSU to eventually, or quickly, blow a pair of 2955/3055.
It's an accident waiting to happen.

+-35Vdc to +-40Vdc would be a safer choice for those devices.
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Old 20th January 2011, 10:59 AM   #12
AJT is offline AJT  Philippines
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Quote:
Originally Posted by xeclipse View Post
EI core measures 2.75 * 3.25 *
2.75 inches and weighs over 3.5(<4) kgs
(7.7 pounds).
i'd say 180 watts is too optimistic for that size traffo, what are your rails?
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Old 20th January 2011, 12:26 PM   #13
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2 pairs of 2sc5200's in quasi complementary with a +/-50v supply.
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Old 20th January 2011, 12:32 PM   #14
AJT is offline AJT  Philippines
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now i am not surprised that your traffo gets hot.....
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Old 20th January 2011, 12:52 PM   #15
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Why bother with quasi comp when you could go fully comp with
C5200/A1943 pairs?
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Old 20th January 2011, 02:33 PM   #16
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Quote:
Originally Posted by Tony View Post
now i am not surprised that your traffo gets hot.....
How much power do you estimate it at?What about the VA?
Quote:
Originally Posted by toprepairman View Post
Why bother with quasi comp when you could go fully comp with
C5200/A1943 pairs?
I couldn't find genuine A1943's...just C5200's.
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Old 20th January 2011, 03:04 PM   #17
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Generally the maximum power that a transformer can transfer from Primary to Secondary is given by the formula:

Core Area = (Square Root of 110% Watts) / 0.0086

If you measure the cross sectional area of the centre leg of the transformer in mm^2

Then Max Power = (Area * 0.0086) ^ 2.

This is then derated by 10%.

I'm making some assumptions here:-

Core Area = 1200mm^2
Max Power = 100VA

Of course the windings may be insufficient to handle this power.

These maths are for Military Grade Transformers using a maximum Flux of 860mT. Our Oriental friends often push the envelope and don't design for 200% reliability as do the MoD.

Last edited by Andy5112405; 20th January 2011 at 03:14 PM.
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Old 20th January 2011, 03:09 PM   #18
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However, pulling more power would only cause the windings to overheat and the transformer to lose regulation.

Core overheating without winding overheating may be due to poor construction or the laminations being shorted together. Ideally the laminated Es and Is should all be insulated from each other by a varnish or oxidised insulating coating. This can be compromised by the mounting bolts fixing the transformer.
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Old 20th January 2011, 04:06 PM   #19
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In normal construction the secondary is at the centre of the transformer with the primary on the outside, unless it is a split bobbin design.

In such a case the secondary could well be overheating and heating up the core, the primary is insulating it so you're not really feeling the heat from where it is being generated.

If you can keep your finger on it for more than 10 seconds it is probably less than 50 degrees C. Not ideal for long term reliability. Transformers should normally run fairly cool.
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Old 20th January 2011, 04:22 PM   #20
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Andy5112405 View Post
In normal construction the secondary is at the centre of the transformer with the primary on the outside, unless it is a split bobbin design.
I thought the primary was protected from damage by being overwound with the secondary.
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