Repurposing old AM IF Transformers? - UK Vintage Radio Repair and Restoration Discussion Forum

Chris55000 · 23rd May 2023, 6:44 am

Now that very cheap old solid–state unwanted am and am/fm only radios are all over the place in charity shops, car boot sales, (and on here sometimes!) etc., is it possible to unwind the old 10 mm square Chinese type I.F. transformers and rewind them to make chroma and subcarrier transformers for pattern generator circuits?

I am thinking in earnest about the desire for a Philips type DEM/Matrix/Phase pattern that has come to light in the Test Card Generator thread, and I was thinking that it should be possible to reuse the can and former from old 10mm 10.7 MHz f.m. IFTs as a starting point, since these are available in abundance from discarded old sets!

What are Member's thoughts on this? I'm happy to give it a go if anyone can enlighten me as to approximate inductances, turns ratios, etc!

What wire diameter would be needed?

Chris Williams

Ed_Dinning · 23rd May 2023, 9:15 am

Hi Chris, there may be a problem if the TCG transformer needs to be wave wound as special equipment will be required. Litz wire is still available it that is required, b ut may not be necessary at 3MHz.

If you can get hold of a Q meter it should be possible to characterise a TCG transformer

Ed

Chris55000 · 23rd May 2023, 9:33 am

Morning Ed!

. . .I have an Advance T2 carefully stacked at the top of my Oscilloscope Racks @ home – will that do?

. . .I also have a modern East Technologies ET4401 LCR Meter, and a Racal 9301A R.F. Millivoltmeter that (I hope!) will read the 4.43 MHz primary and secondary voltages in the '5508 I bought off you!

. . .I haven't read the W.W. and Practical Television articles that cover winding the decoder coils/Transformers in detail yet, but I think they're not wound with very many turns!

What about these Neosid kits as an alternative for winding them on?

Chris Williams

Ed_Dinning · 23rd May 2023, 7:53 pm

Hi Chris the Advance, should give you the information you require. From memory the handbook gives testing details for RF coils/ transformers.
The critical parameters are the inductance, turns ratio, coupling factor and Q of the windings.
The Neosid's might work and worth a try if you have some winding details but I suspect the Al factor (turns per nH) may be incorrect on a different core and Q values could be well different.

Check the Q meter first as it has some horrible black Hunts caps inside

Ed

G6Tanuki · 23rd May 2023, 8:01 pm

In times-past I did things the other way: rewinding PAL-TV sound-IF transformers to 3.5 and 5MHz for amateur-radio applications.

Old TV coil-formers also worked well in building bandpass-couplers. It was always a matter of add a few turns, subtract a few turns and see what happens. Fortunately in the 70s there were plenty of scrap TVs to gralloch for their formers.

23rd May 2023, 6:44 am	#1
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,864	Repurposing old AM IF Transformers? Now that very cheap old solid–state unwanted am and am/fm only radios are all over the place in charity shops, car boot sales, (and on here sometimes!) etc., is it possible to unwind the old 10 mm square Chinese type I.F. transformers and rewind them to make chroma and subcarrier transformers for pattern generator circuits? I am thinking in earnest about the desire for a Philips type DEM/Matrix/Phase pattern that has come to light in the Test Card Generator thread, and I was thinking that it should be possible to reuse the can and former from old 10mm 10.7 MHz f.m. IFTs as a starting point, since these are available in abundance from discarded old sets! What are Member's thoughts on this? I'm happy to give it a go if anyone can enlighten me as to approximate inductances, turns ratios, etc! What wire diameter would be needed? Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

23rd May 2023, 9:15 am	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Repurposing old AM IF Transformers? Hi Chris, there may be a problem if the TCG transformer needs to be wave wound as special equipment will be required. Litz wire is still available it that is required, b ut may not be necessary at 3MHz. If you can get hold of a Q meter it should be possible to characterise a TCG transformer Ed

23rd May 2023, 9:33 am	#3
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,864	Re: Repurposing old AM IF Transformers? Morning Ed! . . .I have an Advance T2 carefully stacked at the top of my Oscilloscope Racks @ home – will that do? . . .I also have a modern East Technologies ET4401 LCR Meter, and a Racal 9301A R.F. Millivoltmeter that (I hope!) will read the 4.43 MHz primary and secondary voltages in the '5508 I bought off you! . . .I haven't read the W.W. and Practical Television articles that cover winding the decoder coils/Transformers in detail yet, but I think they're not wound with very many turns! What about these Neosid kits as an alternative for winding them on? Chris Williams Attached Thumbnails __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 23rd May 2023 at 9:44 am.

23rd May 2023, 7:53 pm	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Repurposing old AM IF Transformers? Hi Chris the Advance, should give you the information you require. From memory the handbook gives testing details for RF coils/ transformers. The critical parameters are the inductance, turns ratio, coupling factor and Q of the windings. The Neosid's might work and worth a try if you have some winding details but I suspect the Al factor (turns per nH) may be incorrect on a different core and Q values could be well different. Check the Q meter first as it has some horrible black Hunts caps inside Ed

23rd May 2023, 8:01 pm	#5
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,995	Re: Repurposing old AM IF Transformers? In times-past I did things the other way: rewinding PAL-TV sound-IF transformers to 3.5 and 5MHz for amateur-radio applications. Old TV coil-formers also worked well in building bandpass-couplers. It was always a matter of add a few turns, subtract a few turns and see what happens. Fortunately in the 70s there were plenty of scrap TVs to gralloch for their formers. __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.