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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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7th Dec 2016, 12:32 am | #1 |
Pentode
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 139
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Earpiece problem
I bought an 330 off Ebay and it turned up with this odd looking earpiece, well I've never come across one before being a bit of a noob to this.
When testing it, it shows open ctt, a visual inspection would suggest it's intact with no obvious breaks on the outside so I'm guessing it's an internal break and so not repairable. Would be very grateful to know if there is anything more that can be done to fix it....? In case I'm missing something blindingly obvious. Thanks |
7th Dec 2016, 12:46 am | #2 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
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Re: Earpiece problem
It's a perfectly normal receiver: 'Receiver 1L', being the older type of receiver as opposed to 'Receiver 2P', being the more efficient, equalised version with the pole-pieces behind a solid wall. Both receivers were made encased in either metal or bakelite.
It should read about 80 Ohms or so on a d.c. measurement. Can you tap into a terminal and the centre-wire joining the two bobbins, or is it too heavily varnished? Have you had the bobbins and magnet out of the case by removing the four screws at the back? It is possible to repair them, but it depands where the break is. I would think it unlikely the break would be buried within the windings unless it's been fiddled with.
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Regds, Russell W. B. G4YLI. |
7th Dec 2016, 6:10 am | #3 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,190
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Re: Earpiece problem
Internal breaks on such coil are, alas, not uncommon. It's the famous 'green spot' corrosion. I have a pair of headphones from a WW2 bit of equipment using a similar design and all 4 coils (2 in each earpiece) are open :-(
It should be possible to rewind the coils (they are not potted), but whether you want to do that is up to you. |
7th Dec 2016, 9:07 am | #4 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
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Re: Earpiece problem
I may have a spare set of coils, already on pole-pieces, if you're really stuck. But have a go first!
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Regds, Russell W. B. G4YLI. |
7th Dec 2016, 10:56 am | #5 |
Pentode
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 139
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Re: Earpiece problem
Thanks for the info chaps. I did take it apart (a little bit) and found that the ends of the windings look in good order and are well connected/soldered to the two "pillars". The windings are joined together between the pole pieces and insulated with a blob of what looks like resin, so I can't even get a reading there. Again, it looks in vgc. The wire itself looks to be well insulated so no chance of a reading elsewhere and no evidence of any fiddling.
So it looks like they are broken some where inside. What's green spot corrosion? Thanks for the offer @Russell_w_b |
7th Dec 2016, 6:43 pm | #6 |
Heptode
Join Date: Jul 2012
Location: Derby DE1, Derbyshire, UK.
Posts: 626
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Re: Earpiece problem
Hi.
Green spot by nature, has a green coloured sticky appearance (Algae) that can form on copper, it's corrosion that eats into the copper with age, all copper will go green with age eventually. Think of it as similar to a copper roof turning green over many years. In old electrical transformers and windings, the green deposits will eat into the copper wire and eventually the result will enevitably be that it will snap, it's your worst enamy in copper windings. Keep transformers and windings as dry as possible, that helps, but it doesn't mean total immunity, the dreaded gundge can still strike at any time. Paul. |
7th Dec 2016, 9:17 pm | #7 | |
Heptode
Join Date: Jan 2008
Location: Hakadal, Norway
Posts: 640
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Re: Earpiece problem
Quote:
dsk |
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7th Dec 2016, 10:10 pm | #8 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,118
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Re: Earpiece problem
Are you sure about the algae? I would have thought that the green is simply copper carbonate (verdigris) that forms as a result of the copper oxidising, then carbon dioxide and water forming a weak carbonic acid with which the copper oxide gradually reacts - or at least that's what I remember from chemistry lessons at school.
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Mending is better than Ending (cf Brave New World by Aldous Huxley) |
7th Dec 2016, 11:45 pm | #9 |
Pentode
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 139
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Re: Earpiece problem
Deffo all there dsk.
Found out tonight one of the bell coils is open ctt. too tonight . The diaphragm looks a bit rusty around the edges so maybe there was some water ingress at some point. Anyway, thanks for all the input, not one of my best buys though |
8th Dec 2016, 1:22 pm | #10 |
Heptode
Join Date: Jul 2012
Location: Derby DE1, Derbyshire, UK.
Posts: 626
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Re: Earpiece problem
Hi Dave,
Yes you are right, that's it, "verdigris" I couldn't remember that word so I was trying to describe it the best way I could Thanks, Paul. |
8th Dec 2016, 3:36 pm | #11 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
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Re: Earpiece problem
I have a few 'Receiver 1L's and they all have a thin yellow varnish over the magnets, the bobbins, and the inside of the case. The later 'Receiver 2P's I have don't seem to be varnished.
Does this 'green spot' verdigris get through varnish, then? I've never had any fail, but I'm certainly mindful of it now!
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Regds, Russell W. B. G4YLI. |
8th Dec 2016, 10:16 pm | #12 |
Heptode
Join Date: Dec 2014
Location: Lincoln, Lincolnshire, UK.
Posts: 583
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Re: Earpiece problem
I came across an old one of mine that has been in store for 10 yers or so. On unscrewing the cover the first thing I noticed was a detached wire. I remember repairing it many years ago for the same problem. I think the wirting is more stressed outside the coils.
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8th Dec 2016, 11:52 pm | #13 |
Pentode
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 139
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Re: Earpiece problem
By way of an update, I unwound one of the coils to find a break about 3/4 of the way in. No sign of corrosion or stressing, just a clean break.
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