|
Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
|
Thread Tools |
26th Sep 2018, 10:30 pm | #41 | ||
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
|
Re: Transformer safety?
Quote:
Quote:
Cheers, GJ
__________________
http://www.ampregen.com |
||
26th Sep 2018, 10:44 pm | #42 | |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,270
|
Re: Transformer safety?
Quote:
__________________
Kevin |
|
26th Sep 2018, 11:10 pm | #43 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
|
Re: Transformer safety?
Faults are just that, faults, and could happen to any equipment, new or old.
Live chassis issues under fault conditions would not seem to be any more dangerous than a live chassis under normal conditions which would have been perfectly acceptable for an ac/dc or autotransformer fed set in original condition. All the ones I have seen (admittedly not a comprehensive sample) have had clear warnings about not removing back panels or covers unless the set is disconnected from the mains supply.
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
26th Sep 2018, 11:19 pm | #44 | ||
Octode
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
|
Re: Transformer safety?
Quote:
If I fitted a mains lead and made the heater functional, I consider, rightly or wrongly, that I am then responsible for it's use by unskilled people. I assessed the risk as being unacceptable. On the other hand, the same friend is destined to get the Volksempfanger radio once I have repaired it. With suitable precautions, such as new three core mains lead and earthed chassis, I consider that the risks of shock or fire are acceptable. I will just have to trust that he will not leave it unattended. So in the end, it's down to our own judgement and what we consider acceptable. Cheers Nick |
||
27th Sep 2018, 12:18 am | #45 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,553
|
Re: Transformer safety?
That electric fire could be fitted with a hard wired RCCD. I am pretty sure I have seen such an item on sale in the past.
Like magic here is the link to such an item. https://www.screwfix.com/p/masterplug-rcd-plug/44855 |
27th Sep 2018, 12:39 am | #46 |
Octode
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
|
Re: Transformer safety?
That's an excellent idea. I've used them before for other things and they are not that expensive. I think it also had a 10ma trip current. I hadn't thought of one in this application though.
In fact, it would be a worthwhile addition to any vintage electronics that are to be given to other people, especially live chassis equipment. I like that idea! Cheers Nick |
27th Sep 2018, 12:59 am | #47 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,553
|
Re: Transformer safety?
I would expect a more thorough search to bring up a 10ma one too judging by how easy it was to find that one.
|
27th Sep 2018, 1:19 am | #48 |
Nonode
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,944
|
Re: Transformer safety?
Whilst Murphy’s exact reasons for choosing an autotransformer power supply for the A362 might remain obscure, evidently it was not to obtain maximum commonality with a corresponding AC-DC model. The A362 autotransformer included a 6.3-volt tapping solely to supply the EABC80 heater. Evidently Murphy saw some benefit (lower hum?) to doing this rather than using say a UABC80 in the series heater chain.
Having opted for the autotransformer with live chassis approach, which precluded protective earthing of the chassis itself, Murphy nonetheless saw fit to provide protective earthing for those parts of the receiver involved in external connections, namely the FM and AM aerials, both via stand-off resistors, and directly, one side of the speaker transformer secondary, from which the external speaker sockets were fed. This required a three-core power lead. The schematic shows that that the earth wire from this went to the earth socket, which was connected to the other earthed items mentioned in the preceding paragraph. Primarily a protective earth, this would also have served as an AM RF earth in the absence of any other arrangements. The provision of an earth socket allowed the connection of external AM aerials with two-wire feeders, such as dipoles or antistatic types. It also allowed the connection of a separate RF earth that was perhaps more direct and less noisy than the protective earth pathway. However, so doing would have created a “back stairs” (and probably very low current capacity) earthing pathway from the protective earthing system, which from the electrical side is generally regarded as something to be avoided. But it did not seem to bother the equipment makers back in the 1950s. Additional to the protective earthing, the autotransformer also had a heat fuse, providing some protection against transformer failure modes that would result in overheating. So overall, Murphy appears to have made some effort on the safety side. In particular, the benefits of providing protective earthing to the “exposed” parts may have been seen as outweighing the possible misperception disbenefit, namely that the presence of a three-core power lead and a transformer could create the impression that this was a mains-isolated receiver with an earthed chassis. Given that the autotransformer fed a half-wave rectifier, then its winding would have had to carry a DC component, and the latter would also have been fed back to the mains. (Putting DC on AC mains was one of the electric utility objections to AC-DC type equipment.) It may be noted that Murphy used similar protective earthing arrangements (to those on the A362) for its contemporary AC-DC receivers, such as the U242. Thus these had three-core power leads. And its contemporary AC-only receivers with double-wound power transformers also had three-core power leads with the earth going to the chassis. Perhaps Murphy had done more than some of the other setmakers in respect of protective measured. But if so, it then appears to have taken a step backwards when it came to its “400” series models. At least the schematic for the A482 AC-only model with double-wound transformer shows it as having a two-core power lead. If that was the case, then the only way of protectively earthing the chassis would have been via the earth socket. And the U472 AC-DC model also had a two-core power lead. The FM aerial was fully isolated by the input RF transformer, the AM aerial was connected to chassis by a standoff resistor, and there was no provision for an external speaker. By way of contrast, the following, from the operating instructions for the Ekco A274, required suspension of disbelief upon initial reading: “Connect the mains lead, by means of a suitable plug, to your electricity supply. The red wire should be connected to Line, the black wire to Neutral, and the green wire to Earth. If only a two-pin mains outlet is available, cut back the green wire so that it cannot enter the plug.” And this was for a receiver that had abundant external interconnection possibilities, each with one side connected to chassis, and which were evidently intended for actual use, not just ornamental. That Ekco felt that it had to cater for the possibility of power outlets without an earth connection for what was a 1956 model does suggest that the UK may have been rather late in the general adoption of protective earthing for domestic appliances, at least in comparison with “down-under” practice. Here in New Zealand, I don’t recall seeing other than three-pin power outlets, nor any locally-made radio receivers that did not have three-core power leads. Perhaps that was because the idea of protective earthing had a relatively early start. Multiple-earthed neutral (MEN) distribution was a national standard from 1920, and part of this was that each consumer had a local earth, with neutral bonded to that earth (by the MEN-link) in consumer switchboards. I can recall from my childhood early discussions with available/interested adults (back in the 1950s) about electrical matters that the importance of good earthing was frequently stressed. Cheers, |
27th Sep 2018, 9:32 am | #49 | |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
|
Re: Transformer safety?
Quote:
https://www.vintage-radio.net/forum/...d.php?t=145497 Its amounts to a list of my and other peoples "guesses" as to the reason(s) but no definitive conclusion was arrived at. |
|
27th Sep 2018, 11:21 pm | #50 | |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,567
|
Re: Transformer safety?
Quote:
I started playing about with TV when I was about 14 and was fully aware of the live chassis situation. It was second nature to hold a neon screwdriver to the chassis and reverse the plug if necessary. Note that I have NEVER had a shock from a live-chassis set either TV or radio. They are no more dangerous to work on than an isolated chassis at least not to me. The first company I worked for didn't even have isolation transformers (OK they wouldn't get away with that now). I do use an isolation transformer on my bench at home but that is mainly so that I can connect earthed test equipment (signal generators , scopes etc) to live-chassis TVs and radios. Sometimes one of my restored TV's will develop a fault and I don't always lug the thing up on to the bench to give it an initial inspection so very often my initial checks are on non-isolated mains. I still check that the chassis is at mains neutral though. Obviously it's up to the individual as to how they approach live-chassis sets. If you don't like them then avoid them but in general, if the chassis is at mains neutral, they are no more dangerous to work on than an isolated chassis. Note that these are my opinions. Others may (and are entitled to) disagree!
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
|
28th Sep 2018, 2:14 am | #51 | ||
Hexode
Join Date: Oct 2017
Location: Manchester, UK.
Posts: 363
|
Re: Transformer safety?
[QUOTE=GrimJosef;1078642]
Quote:
Quote:
|
||
28th Sep 2018, 9:02 am | #52 | |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
|
Re: Transformer safety?
Quote:
If, on the other hand, you are repairing just one vintage heater for someone you know well enough to call a friend, and if you can tell him how to use it safely as many times as necessary before you hand it back to him, then maybe the rules can be relaxed a smidgen ? As for the untrustworthiness of the general public, the same logic that says we can't explain to them how to use electrical gear safely would also say that they shouldn't be trusted with a gas hob or with a lawnmower or (oh my lord !) with walking along a pavment with nothing at all separating them from fast moving traffic . I just don't know how there's anyone left alive ! The fact is, most people aren't daft. If they can learn to drive a car then they can learn to use a heater. Cheers, GJ
__________________
http://www.ampregen.com |
|
28th Sep 2018, 9:09 am | #53 | |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,567
|
Re: Transformer safety?
Quote:
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman..... Last edited by Sideband; 28th Sep 2018 at 9:16 am. |
|
28th Sep 2018, 10:50 am | #54 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,553
|
Re: Transformer safety?
That sounds like that story I was told by a TV engineer back in the day.
It was a very posh estate and a woman had called the power company out because the electricity was making a funny noise. When the power sparky arrived he had a listen and realised that the electricity was indeed making a funny noise but only what was being consumed by the alarm on near by house that had been robbed. |
28th Sep 2018, 12:59 pm | #55 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
|
Re: Transformer safety?
On the odd occasion when someone has asked me to repair an item of electrical equipment, the first thing I do is to give that item an initial inspection. A written report is then given to the owner of that item. On that report, the following appears:
Electrical Safety: Please note that it may be necessary to make design changes to any hardware that you supply to me in order to render such hardware electrically safe. Any such changes that are made will be fully documented and passed on to you. If you do not wish me to make any such changes you must notify me, in writing, prior to any repair work taking place. All electrical equipment that is serviced by me is electrically safety tested prior to return to its owner. You will be notified (in writing) of any possible short-comings arising from that test. Please sign below to signify that you have read the above and are in agreement with it. Thank you. The customer gets the original; I keep a copy. There have been the rare cases when an item is in such a dangerous condition (due to age or its intrinsic design) that I will refuse to attempt any repairs: the owner has then always been informed accordingly. Al. |
28th Sep 2018, 3:20 pm | #56 |
Octode
Join Date: Mar 2006
Location: Watford, Hertfordshire, UK.
Posts: 1,270
|
Re: Transformer safety?
As someone who lived through the 50's as a kid, an Earth connection was unheard of, except that there was a terminal on Dad's radio that was marked for that but Dad only fitted an Aerial. Everything at home was run from one 15A two pin socket, smaller 5A plugs accommodated with a simple multi-way adaptor bought from Woolies. Even Mum's iron was plugged into the light using a bayonet plug. It wasn't until the arrival of the washing machine that an earth wire was run for it, connected at that time to the lead water pipe. Later of course, my elder brother and I re-wired the place to full IEE regs. But I often think of how many two-wired systems there must have been around in the 50's and no doubt a lot of radio sets were made with this in mind. I have seen far more horrors, at the shop I worked at, they would sell heaters for the nurses in a local hospital to cook with. These were small square metal boxes with an exposed spiral element positioned under a simple saucepan rest, made of just a few metal rods. The world really was a far different place then.
__________________
Whether the Top Cap is Grid or Anode - touching it will give you a buzz either way! |
28th Sep 2018, 3:22 pm | #57 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,642
|
Re: Transformer safety?
No win no fee was a disaster still waiting to happen then!
|
28th Sep 2018, 3:41 pm | #58 | |
Nonode
Join Date: Feb 2005
Location: Worcestershire, UK.
Posts: 2,533
|
Re: Transformer safety?
Quote:
Steve |
|
28th Sep 2018, 3:53 pm | #59 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
|
Re: Transformer safety?
The huge improvements in automotive safety standards over the years (I started to list them, but to be honest there have been too many) have led to a large and well understood fall in annual road injuries and fatalities, especially when corrected for the much larger volumes of traffic these days.
But I'd be really interested to know if there's been any substantial fall in casualties brought about by more and more strict electrical/electronic regulations. If I had to guess I might guess that fires caused by electrical equipment are less common (perhaps a lot less common) these days. But I wonder whether real injuries and deaths from electric shock were once very common and are now very rare ? I suspect that in fact they've actually never been very common. Modern equipment is so safe that you can treat it however you like and it won't hurt you. Decades ago it wasn't, so you had to be a bit careful, but if you were it wouldn't hurt you back then either. So perhaps the major result of all the safety improvements, in terms of electric shock at least, has simply been 'dumbing down' ? I honestly don't know if there's any truth in this though. Does anyone ? Cheers, GJ
__________________
http://www.ampregen.com |
28th Sep 2018, 3:55 pm | #60 | |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
|
Re: Transformer safety?
Quote:
"O.K., now it works: that'll do. So why do I need an 'earth' wire? Mother, put the kettle on; let's listen to Mrs. Dale's Diary". Indeed, the world really was a very different place then. Al. |
|