Burnt out HRO Ant Coil repair - UK Vintage Radio Repair and Restoration Discussion Forum

G4_Pete · 10th Dec 2014, 8:20 pm

Hi,
I am trying to restore a 1.7 - 4Mhz band spread coil which has burnt out and been repaired sometime in the past.

photos attached.

I suspect someone transmitted power into the front end of the HRO as the former is very badly charred with smoke staining all over the inside of the can and on the capacitors. The secondary is intact but burnt black and although it seems to tune I can’t trust it to stay that way. The Bakelite type material base antenna contacts no 4/5 also have heat damage with some bubbling on the surfaces but unless they have tracked through this should not matter. This must have been a very long time ago as there is no residue smell.

As I use my HRO on air It has certainly made me think a bit about aerial switching and coil protection so that none of mine suffer this fate.

2 Questions.

1. What is the former made of? - could it contain asbestos as the burnt bits are white and flaky. I will treat it as if it does contain asbestos has but it would be nice to know.

2. Has anyone got a scrap beyond repair 1.7 - 4.0 'D1' coil or just the former although mine is band spread I believe the coil winding is the same on the non-band spread coil.

I will make and wind a new one but just checking for advice or what is around first.

Pete

HamishBoxer · 10th Dec 2014, 9:13 pm

Not sure what amount of RF would do that.Unsure but never heard of asbestos in HRO coils so I stand to be corrected.
What not try Ebay for a replacement coil pack if no one on the forum has one? Wanted Ad possibly on here worth a go.

10th Dec 2014, 9:20 pm

Quite frankly, any old bit of plastic tube (tube, because it's mainly air) of the same size will do.

BobGreen · 10th Dec 2014, 9:48 pm

I have a 1.7 - 4MHz coil pack with the right hand coil wrecked by my trying to make it oscillate at 50 MHz for the 6M band. The three RF coils to the left are untouched and you can have it for £10 plus £5 shipping.

I have taken out the left hand 1st RF coil and it looks nothing like your photo. It has two Pi wound sections on a "Perspex" former.

You can make a perfect coil set if you combine your oscillator coil with what I offer. Let me know.

Scottart · 13th Dec 2014, 5:04 pm

Pete,

I've a spare bakelite former, same diameter and length ( 1" x 1.5" ) as your 1.7 - 4MHz D coil, but from a higher freq setup. The former is in good condition.
It's FOC.

Stephen

ms660 · 13th Dec 2014, 7:07 pm

National used R39 material for some of their coil forms in the '30's, they might have used mica filler as opposed to wood dust, can't remember for sure.

Lawrence.

G4_Pete · 14th Dec 2014, 11:24 am

Hi,
Thanks everyone for assistance I have some bits on the way to me shortly.

I used to turn bobbins and wind precision resistance coils and could have exactly replicated one of these formers in about 10 mins but alas no access to machines now and all my friends who did have have retired.

Small lathe - something else for the wish list!

Pete

10th Dec 2014, 8:20 pm	#1
G4_Pete Hexode Join Date: Feb 2014 Location: Southampton, Hampshire, UK. Posts: 419	Burnt out HRO Ant Coil repair Hi, I am trying to restore a 1.7 - 4Mhz band spread coil which has burnt out and been repaired sometime in the past. photos attached. I suspect someone transmitted power into the front end of the HRO as the former is very badly charred with smoke staining all over the inside of the can and on the capacitors. The secondary is intact but burnt black and although it seems to tune I can’t trust it to stay that way. The Bakelite type material base antenna contacts no 4/5 also have heat damage with some bubbling on the surfaces but unless they have tracked through this should not matter. This must have been a very long time ago as there is no residue smell. As I use my HRO on air It has certainly made me think a bit about aerial switching and coil protection so that none of mine suffer this fate. 2 Questions. 1. What is the former made of? - could it contain asbestos as the burnt bits are white and flaky. I will treat it as if it does contain asbestos has but it would be nice to know. 2. Has anyone got a scrap beyond repair 1.7 - 4.0 'D1' coil or just the former although mine is band spread I believe the coil winding is the same on the non-band spread coil. I will make and wind a new one but just checking for advice or what is around first. Pete Attached Thumbnails

10th Dec 2014, 9:13 pm	#2
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: Burnt out HRO Ant Coil repair Not sure what amount of RF would do that.Unsure but never heard of asbestos in HRO coils so I stand to be corrected. What not try Ebay for a replacement coil pack if no one on the forum has one? Wanted Ad possibly on here worth a go. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

10th Dec 2014, 9:20 pm	#3
Guest Guest Posts: n/a	Re: Burnt out HRO Ant Coil repair Quite frankly, any old bit of plastic tube (tube, because it's mainly air) of the same size will do.

10th Dec 2014, 9:48 pm	#4
BobGreen Retired Dormant Member Join Date: Jan 2011 Location: Egham, Surrey, UK. Posts: 219	Re: Burnt out HRO Ant Coil repair I have a 1.7 - 4MHz coil pack with the right hand coil wrecked by my trying to make it oscillate at 50 MHz for the 6M band. The three RF coils to the left are untouched and you can have it for £10 plus £5 shipping. I have taken out the left hand 1st RF coil and it looks nothing like your photo. It has two Pi wound sections on a "Perspex" former. You can make a perfect coil set if you combine your oscillator coil with what I offer. Let me know.

13th Dec 2014, 5:04 pm	#5
Scottart Pentode Join Date: Apr 2005 Location: London, UK. Posts: 205	Re: Burnt out HRO Ant Coil repair Pete, I've a spare bakelite former, same diameter and length ( 1" x 1.5" ) as your 1.7 - 4MHz D coil, but from a higher freq setup. The former is in good condition. It's FOC. Stephen Attached Thumbnails

13th Dec 2014, 7:07 pm	#6
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Burnt out HRO Ant Coil repair National used R39 material for some of their coil forms in the '30's, they might have used mica filler as opposed to wood dust, can't remember for sure. Lawrence.

14th Dec 2014, 11:24 am	#7
G4_Pete Hexode Join Date: Feb 2014 Location: Southampton, Hampshire, UK. Posts: 419	Re: Burnt out HRO Ant Coil repair Hi, Thanks everyone for assistance I have some bits on the way to me shortly. I used to turn bobbins and wind precision resistance coils and could have exactly replicated one of these formers in about 10 mins but alas no access to machines now and all my friends who did have have retired. Small lathe - something else for the wish list! Pete