|
General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
|
Thread Tools |
7th Sep 2016, 10:40 pm | #21 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
|
Re: Plastics that deteriorate
PVC sleeving does silly things if in contact with polystyrene, that's why power leads for appliances are packed in a polythene bag, and not put in direct contact with polystyrene packing foam.
Last edited by kalee20; 7th Sep 2016 at 10:41 pm. Reason: Spelling |
7th Sep 2016, 10:45 pm | #22 |
Dekatron
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
|
Re: Plastics that deteriorate
Funnily enough, I saw this youtube video a few weeks back....
It covers and explains this issue. It's also worth reading the 'show more' text below the video on youtube. Sadly, I think he threw the tools away because it looks like there is no cure for this issue. https://www.youtube.com/watch?v=KTxkunC0Lo8
__________________
Regards, Jeremy G0HZU |
8th Sep 2016, 12:09 am | #23 |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
|
Re: Plastics that deteriorate
The 'green goo' exudate from PVC cables is not always significantly conductive as the video text implies. The phthalate plasticiser released from the PVC itself is insulative, I think the breakdown voltage falls somewhat according to how much copper oxide it picks up as it reacts with the conductor. I have certainly tested affected cables where it did not measurably reduce the insulation resistance even where the terminations were coated with goo, IIRC they all exceeded 200MΩ at 500V DC. However, where there is goo, there is cable insulation lacking its plasticiser that will become embrittled and at risk of cracking away from the conductors if disturbed, so replacement is indicated. Only cables from around the late 60s are involved, as the suspect PVC formulation was phased out.
The related problem of plasticiser being leached from PVC by contact with polystyrene of course can affect cables of any age. When expanded polystyrene foam was widely used as cheap thermal insulation e.g. on boats, and PVC cables were run in contact with it before the problem was realised, the resulting damage in some cases necessitated a rewire. As with green goo, the warmer a cable runs the more rapid the deterioration. Small clear plastic parts drawers and trays are often made of polystyrene. PVC parts stored in these will react with and stick to, even eat through, the bottom of the tray. I had a PVC cable grommet kit from RS supplied in a polystyrene 18-compartment box, into which the grommets started to embed until I transferred them to a similar tray made of HDPE. I'm not sure if binder hydrolysis in magnetic tapes (aka sticky shed) qualifies for this thread as it's only the coating, not the tape base, that is breaking down. It is the degenerative mechanism that I have had most cause to study as my best and favourite recordings, from when I was learning the art and craft of recording, are badly affected. Most were made on second-hand Ampex 406 and 456 from the early 1980s, which is a consistent offender. Have we covered urethane foam yet? I have an electromechanical voltmeter to restore that contains uniselectors, the noise of which was muffled by lining the case with foam. It has deteriorated into blobs of sticky goop that have got into the uniselectors and stuck all over the contacts and moving parts. Nasty! |
8th Sep 2016, 2:02 am | #24 |
Heptode
Join Date: Jul 2012
Location: Daylesford, Victoria, Australia
Posts: 674
|
Re: Plastics that deteriorate
On the subject of PVC, is there anything you can apply to it to keep it soft, or soften it if it's starting to harden? I've had this problem with Beyer DT100 headphones; the ear pads go hard and the headband padding cracks.
Those Ampex tapes were awful. I tried to tell the technical guy that when I was a film student, and he got annoyed with me. I mean, I only used the stuff, he was the one who'd approved it! I prefer the 60s pink-backed BASF tapes, they last for ever.
__________________
The Waves That Rule Britannia |
8th Sep 2016, 8:59 am | #25 | |
Heptode
Join Date: Jul 2014
Location: Boston, Lincolnshire, UK.
Posts: 992
|
Re: Plastics that deteriorate
Quote:
|
|
9th Sep 2016, 1:53 am | #26 | |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
|
Re: Plastics that deteriorate
Quote:
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments. |
|
14th Sep 2016, 7:48 am | #27 | |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,809
|
Re: Plastics that deteriorate
Quote:
__________________
A digital radio is the latest thing, but a vintage wireless is forever.. |
|
14th Sep 2016, 8:49 am | #28 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
|
Re: Plastics that deteriorate
I was going to mention PVC grommets (and sleeving) too til Lucien mentioned it. The popular 'Raaco' component drawers were polystyrene (brittle & clear) but have changed now to IMHO polythene (flexible & opaque). So, if you have problems with plastic bits in old drawers, just order replacement drawers from rs/farnell/cpc, as they are cheap.
I keep my grommets in a linbin these days.
__________________
Kevin |