Headphones mystery - UK Vintage Radio Repair and Restoration Discussion Forum

Pete_kaye · 18th Jun 2022, 6:22 pm

I was given these today and measured 19k total with one side 2 and the other 17k, total 19k. How could thus be? The leads gave 1 ohm each. They look identical inside . Later I will test in a crystal set.

peter_sol · 18th Jun 2022, 7:55 pm

The side you show says 2000ohms. What does the other side say? I assume you mean the resistance measured.

Pete_kaye · 19th Jun 2022, 8:17 am

They are a matched pair in a headband. There was also a single Brandes headphone at 1000 ohms. A pity the other one is missing.

lesmw0sec · 19th Jun 2022, 9:27 am

It would appear that if they are an identical pair, there is a problem with the HR one. Have a look to see if there is any green corrosion where the coils terminate inside.

David Simpson · 19th Jun 2022, 10:50 am

Should be 2K ohm, not 20ish. The leads look a bit tatty. If they are re-usable, the contact ends would need re-whipping & tinning. As the conductors are a mixture of fine copper & very fine thread - to give them flexibility.

Regards, David

Pete_kaye · 20th Jun 2022, 6:06 pm

As expected , the volume in the one is good but the other quiet. I am leaving them in the sun with the diaphragms off until I delve deeper. Perhaps the bad contact is inside the coil?☹️
The diaphragms slide off easily and I remember re-magnetising inside once . Is there a link somewhere on this?

Pete_kaye · 21st Jun 2022, 9:19 am

Overnight, the resistance in the left hand coil has dropped to 9k, as seen in my photo. Would putting higher voltage through it do any good / harm? What is a safe voltage to use, in general?

PJL · 21st Jun 2022, 3:14 pm

These are often faulty and it will need a rewind. Pretty easy to do but requires very thin gauge wire, a jig, and lots of care and patience. I have done quite a few...

PJL · 21st Jun 2022, 6:10 pm

FMC will be Fellows Magneto Company and I see they are using the 'Type Approved...' BBC stamp.

Silicon · 21st Jun 2022, 9:00 pm

If there is any dampness or corrosion between the metal components (i.e. bolts washers, etc)
you could get additional resistances or small voltages which would affect the test meter.

18th Jun 2022, 6:22 pm	#1
Pete_kaye Octode Join Date: Jun 2005 Location: Sheffield, South Yorkshire, UK. Posts: 1,227	Headphones mystery I was given these today and measured 19k total with one side 2 and the other 17k, total 19k. How could thus be? The leads gave 1 ohm each. They look identical inside . Later I will test in a crystal set. Attached Thumbnails

18th Jun 2022, 7:55 pm	#2
peter_sol Octode Join Date: Aug 2003 Location: Welwyn Garden City, Herts. UK. Posts: 1,906	Re: Headphones mystery The side you show says 2000ohms. What does the other side say? I assume you mean the resistance measured.

19th Jun 2022, 8:17 am	#3
Pete_kaye Octode Join Date: Jun 2005 Location: Sheffield, South Yorkshire, UK. Posts: 1,227	Re: Headphones mystery They are a matched pair in a headband. There was also a single Brandes headphone at 1000 ohms. A pity the other one is missing. Attached Thumbnails

19th Jun 2022, 9:27 am	#4
lesmw0sec Octode Join Date: Jul 2009 Location: Carmel, Llannerchymedd, Anglesey, UK. Posts: 1,509	Re: Headphones mystery It would appear that if they are an identical pair, there is a problem with the HR one. Have a look to see if there is any green corrosion where the coils terminate inside.

19th Jun 2022, 10:50 am	#5
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,858	Re: Headphones mystery Should be 2K ohm, not 20ish. The leads look a bit tatty. If they are re-usable, the contact ends would need re-whipping & tinning. As the conductors are a mixture of fine copper & very fine thread - to give them flexibility. Regards, David

20th Jun 2022, 6:06 pm	#6
Pete_kaye Octode Join Date: Jun 2005 Location: Sheffield, South Yorkshire, UK. Posts: 1,227	Re: Headphones mystery As expected , the volume in the one is good but the other quiet. I am leaving them in the sun with the diaphragms off until I delve deeper. Perhaps the bad contact is inside the coil?☹️ The diaphragms slide off easily and I remember re-magnetising inside once . Is there a link somewhere on this?

21st Jun 2022, 9:19 am	#7
Pete_kaye Octode Join Date: Jun 2005 Location: Sheffield, South Yorkshire, UK. Posts: 1,227	Re: Headphones mystery Overnight, the resistance in the left hand coil has dropped to 9k, as seen in my photo. Would putting higher voltage through it do any good / harm? What is a safe voltage to use, in general? Attached Thumbnails

21st Jun 2022, 3:14 pm	#8
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Headphones mystery These are often faulty and it will need a rewind. Pretty easy to do but requires very thin gauge wire, a jig, and lots of care and patience. I have done quite a few...

21st Jun 2022, 6:10 pm	#9
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Headphones mystery FMC will be Fellows Magneto Company and I see they are using the 'Type Approved...' BBC stamp.

21st Jun 2022, 9:00 pm	#10
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,171	Re: Headphones mystery If there is any dampness or corrosion between the metal components (i.e. bolts washers, etc) you could get additional resistances or small voltages which would affect the test meter.