If Transformer rewinding - UK Vintage Radio Repair and Restoration Discussion Forum

zak · 24th Feb 2005, 9:37 pm

Can anyone help in getting an IF tranformer (for Ekco AC85) or of getting it rewound.The tuned frequency is 110kc/s,so its quite a few turns and wavewound as well.Someone has tried to pilewind a coil,but must have gave up.Has anyone attempted a rewind or a rebuild?

Station X · 25th Feb 2005, 12:37 pm

Hello Zak.

You don't know what you can do until you've tried. If you can't get a replacement transformer I'd attempt a rewind. You can't end up any worse than when you started and you have a good chance of success.

You can get wire from "The Scientific Wire Company". They have a website. One tricky job is soldering coated wire. Some is self-fluxing and the heat of soldering will remove the coating, but some isn't. Trying to melt the insulation with a match just melts the wire. I have found that gentle scraping with a razor blade does the trick. Make sure that the terminations aren't under any strain, as this is where the wire is most likely to break.

From your description it sounds like the wire is self supporting. so it might be necessary to make a couple of side cheeks from say printed circuit board with the copper removed. These can be glued or press fitted to the former.

Don't attempt to wind the coil with a power drill rotating the former. The wire will just break. Best way is to use a hand drill held in a vice. If you want to use power an electric screwdriver is best.

As you probably don't know the number of turns it's a case of suck it and see. "Scramble" winding should be OK. Wind on too many turns to start with and then check the resonant frequency using a sig generator and scope or a valve voltmeter. Do this with the core in various positions. With any luck you'll find the frequency is too low and you'll need to remove some turns.

Good Luck.

Graham.

Ed_Dinning · 25th Feb 2005, 1:27 pm

Hi Zak, cardboard may be better than PCB material as it has a lower Er and will give lower self capacitance and higher Q. If you know anyone with a Q meter you can use that is an easy way to set the coil up. The old dodge for insulated wire was to use a small meths burner to remove the insulation. This was about the only way to do it if you were using Litz wire, which is probably not necessary at 110KHz.

Ed

zak · 25th Feb 2005, 8:45 pm

Thanks folks,I am going to give it a try,I will try paxolin cheeks as they would be more rigid to support a winding of a 1/4" high or so,and I have little to lose.I have removed the transformer and the set appears to work fine,although strong signals are distorted (the transformer is a 1:1 ratio that only feeds the AVC diode),at least this enables the set to be used while this job is undertaken.

24th Feb 2005, 9:37 pm	#1
zak Retired Dormant Member Join Date: Feb 2005 Location: Monmouthshire,on South Wales border Posts: 85	If Transformer rewinding Can anyone help in getting an IF tranformer (for Ekco AC85) or of getting it rewound.The tuned frequency is 110kc/s,so its quite a few turns and wavewound as well.Someone has tried to pilewind a coil,but must have gave up.Has anyone attempted a rewind or a rebuild?

25th Feb 2005, 12:37 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: If Transformer Help Hello Zak. You don't know what you can do until you've tried. If you can't get a replacement transformer I'd attempt a rewind. You can't end up any worse than when you started and you have a good chance of success. You can get wire from "The Scientific Wire Company". They have a website. One tricky job is soldering coated wire. Some is self-fluxing and the heat of soldering will remove the coating, but some isn't. Trying to melt the insulation with a match just melts the wire. I have found that gentle scraping with a razor blade does the trick. Make sure that the terminations aren't under any strain, as this is where the wire is most likely to break. From your description it sounds like the wire is self supporting. so it might be necessary to make a couple of side cheeks from say printed circuit board with the copper removed. These can be glued or press fitted to the former. Don't attempt to wind the coil with a power drill rotating the former. The wire will just break. Best way is to use a hand drill held in a vice. If you want to use power an electric screwdriver is best. As you probably don't know the number of turns it's a case of suck it and see. "Scramble" winding should be OK. Wind on too many turns to start with and then check the resonant frequency using a sig generator and scope or a valve voltmeter. Do this with the core in various positions. With any luck you'll find the frequency is too low and you'll need to remove some turns. Good Luck. Graham.

25th Feb 2005, 1:27 pm	#3
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,195	Re: If Transformer Help Hi Zak, cardboard may be better than PCB material as it has a lower Er and will give lower self capacitance and higher Q. If you know anyone with a Q meter you can use that is an easy way to set the coil up. The old dodge for insulated wire was to use a small meths burner to remove the insulation. This was about the only way to do it if you were using Litz wire, which is probably not necessary at 110KHz. Ed

25th Feb 2005, 8:45 pm	#4
zak Retired Dormant Member Join Date: Feb 2005 Location: Monmouthshire,on South Wales border Posts: 85	Re: If Transformer Help Thanks folks,I am going to give it a try,I will try paxolin cheeks as they would be more rigid to support a winding of a 1/4" high or so,and I have little to lose.I have removed the transformer and the set appears to work fine,although strong signals are distorted (the transformer is a 1:1 ratio that only feeds the AVC diode),at least this enables the set to be used while this job is undertaken.