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Old 27th Nov 2021, 12:28 pm   #1
Gabe001
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Default Transformer saturation question

Just want to pick your brains on a transformer issue

I've got a transformer (from an amplifier) I'd like to put back into service. I haven't tested it yet, so the following applies only in principle

It had been operational in the previous circuit with the following parameters:
HT 250 @ 118mA
Heater winding 6.3v 1.8a
Rectifier 5v 3a (5u4g - overkill I know)

The circuit I intend to use it in has the following operational parameters:

HT 250 @ 132mA
Heater winding 6.3v 1.8a
Rectifier 5v 2a (gz34 or 5v4)

So a higher overall HT current but a lower rectifier current with the total wattage remaining pretty much the same; if anything slightly lower in the second configuration

Is this likely to be ok or are we dealing with a non starter?

Thanks
Gabriel
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Old 27th Nov 2021, 1:40 pm   #2
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Default Re: Transformer saturation question

That will be fine, I have a transformer which only had the (UK) manufacturer and a part number on it. I rang them and the nice chap on the 'phone said, "it's one of our 250V 150mA (single winding), 6,3V 2A, you can get a bit more out of one winding if the other isn't loaded too much", or words to that effect.
 
Old 27th Nov 2021, 2:20 pm   #3
Ed_Dinning
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Default Re: Transformer saturation question

Hi Gabe, it will not immediately burst into flames but fuse it closely and keep an eye on its temperature. depending on duty cycles it should be fine. Obviuosly not suitable for 24/7 use

Ed
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Old 27th Nov 2021, 2:34 pm   #4
kalee20
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Default Re: Transformer saturation question

Exactly as MM says!

The total loading being the same, the losses in the primary will be the same (the primary winding can't 'know' which of its secondaries is sucking the power).

The reduction in loading on the 5V winding will result in less loss here. The increase in loading on the 250V winding will result in more loss here. In an absolutely-optimally designed transformer, where bobbin area occupied by a winding is proportioned according to its loading, the original loading would give minimum total losses and the shift would actually give a very slight rise. But it's a broad minimum, and with the design constrained by available wire sizes etc it's just as likely that the shift will be towards the minimum as away from it, anyway.

Finally, increasing the loading won't cause saturation! The magnetism in the core is independent of loading (in fact, owing to primary losses, increasing the loading actually moves the thing AWAY from saturation). So, use with confidence!
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Old 27th Nov 2021, 2:37 pm   #5
Gabe001
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Default Re: Transformer saturation question

Thanks ed and Merlin for the reassurance. Definitely not running 24/7 and the current draw at normal listening levels will be a bit more reasonable.

Gabriel
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Old 27th Nov 2021, 4:01 pm   #6
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Default Re: Transformer saturation question

Another thing that may be applicable, most radios used their output valves at near the maximum allowable to give the most output. Hardly ever needed but good advertising, upping the cathode resistor by a factor of two really helps with longevity and you won't notice the lack of power.
 
Old 27th Nov 2021, 5:52 pm   #7
its ur aerial
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Default Re: Transformer saturation question

Agree totally with all the others, cant see a problem, but keep your eyes on it first time being used, if really concerned you could always measure the current being pulled on the HT winding.

Ken, G6HZG, VMARS, AM ARS.
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Old 27th Nov 2021, 6:31 pm   #8
Gabe001
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Default Re: Transformer saturation question

Thanks again for all the comments. Will do.
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