transformer advice needed

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Steptoe
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#1 transformer advice needed

Post by Steptoe »

I have a collection of ex GPO transformers and am trying to work out how to use them. They have a nickel/iron gapped core and four identical windings, each of which consists of two parallel wires. The winding starts in the middle of the wire and each end is then wound round the core in opposite directions. Each half winding is then buried beneath a different half winding, resulting in a very complex arrangement. I am puzzled as to why they needed to be made in this way, but more particularly, can they be used as audio transformers? By linking them up I can increase the turns ratio to something more useful than3;1, but is there a reason why this is not desirable, apart from the weight? I tried putting the mains across all four windings in series but the noise was not encouraging. Each winding has a dc resistance of 9 ohms.

Many thanks. Steptoe.
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pre65
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#2

Post by pre65 »

I was reading a post about output transformers for PT15 (on another forum) by James D, and he was saying the inductance was important, and 45H or more was ideal.

My big Hammonds (1642SE) come in at 53H and 5K so should be OK when I get round to PT15 again.

So Steptoe, do you know the inductance of these GPO transformers ?
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Mike H
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#3

Post by Mike H »

I'm guessing was primarily for telephone use so will be voice only type of bandwidth ~ i.e. don't expect much bass, possibly...

You can test the inductance by doing this:

http://www.audio-talk.co.uk/phpBB2/viewtopic.php?t=4240
 
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Paul Barker
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#4

Post by Paul Barker »

Picture against a known object like a valve?
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Steptoe
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#5 transformer advice needed.

Post by Steptoe »

Dear All, once again, many thanks for your input. Sorry I have taken a long time to reply but efficiency is not my middle name and most of my time is spent trying to emulate a man with no legs. The transformers measure 2x2x4 inches including the can and weigh about 500 grams.
Although I fully appreciate that the frequency response will be very limited as Mike suggested, would it be possible to extend it either up or down by using a number of them connected in series, parallel or a mixture of the two? I know this is an unusual approach but the idea of buying anything when something you already have may do, is anathema to those of us who grew up in Liverpool. If anyone would like some to try, please let me know. Yours sincerely, Steptoe.
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pre65
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#6

Post by pre65 »

Steptoe, I applaud your determination to recycle old equipment that probably came to you at no cost, BUT - do you want something that just "makes a noise" , or a quality amplifier.

If the latter, why not just sell a few of the desirable valves in your collection (PX4 - 4212 -4211 etc) and buy yourself some half decent transformers.

What I'm doing will (I hope) show you what certain valves can do, but only with good quality partnering equipment. :wink:
The only thing necessary for the triumph of evil is for good men to do nothing.

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#7 transformer advice needed

Post by Steptoe »

Dear Pre 65. What you are asking me to do is nothing less than abandoning the culture of a lifetime, learned at my father's knee. I know in my heart that you are absolutely correct but it is taking some time for me to come to terms with a concept which is so alien to everything I was taught. I have, however, just had a look at the amplifier, which is magnificent and have no doubt that hearing it in action will enable me to finally bite the bullet and transfer my thought processes into the 21st century. With best wishes, Steptoe.
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Mike H
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#8

Post by Mike H »

OK, so the can is 2 x 2 x 4", therefore the transformer inside is tiny. Only 500g for the whole thing. To 'do' reasonable LF it would have to be in kilograms, say 4 - 5 kg.

You might be able to increase the primary inductance by wiring the primaries of 2 or more in series, BUT all the secondaries in parallel. This would also increase the turns ratio > 3:1. (I presume that's the basic turns ratio.) Worth an experiment.
 
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pre65
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#9

Post by pre65 »

Mike H wrote:OK, so the can is 2 x 2 x 4", therefore the transformer inside is tiny. Only 500g for the whole thing. To 'do' reasonable LF it would have to be in kilograms, say 4 - 5 kg.

You might be able to increase the primary inductance by wiring the primaries of 2 or more in series, BUT all the secondaries in parallel. This would also increase the turns ratio > 3:1. (I presume that's the basic turns ratio.) Worth an experiment.
I've got one here, was going to bring it to Owston for critical acclaim. :wink:
The only thing necessary for the triumph of evil is for good men to do nothing.

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