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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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16th May 2022, 7:37 pm | #1 |
Tetrode
Join Date: Oct 2013
Location: Guildford, Surrey, UK.
Posts: 82
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AC/ DC radios live chassis.
Hello, on an AC / DC chassis like the Marconi T18DA which has a live chassis should the neutral go to the chassis? The existing mains wire is not colour coded.
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16th May 2022, 8:03 pm | #2 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: AC/ DC radios live chassis.
AC/DC sets are not very safe under any circumstance but the T18DA does have a double pole mains switch so the side that switches to the chassis should be connected to Neutral. Many of the cheap imported USA sets have a single pole switch that disconnects the connection to chassis and if you connect this to neutral then the heater chain will make the chassis LIVE when switched off (only solution is to change the switch for double pole).
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16th May 2022, 8:39 pm | #3 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,059
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Re: AC/ DC radios live chassis.
Yes, the neutral should go to chassis if possible. (If you're operating it on DC and the positive happens to be grounded, you don't have a choice of course!)
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16th May 2022, 9:03 pm | #4 |
Nonode
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,358
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Re: AC/ DC radios live chassis.
Ideally, operate it using an isolating mains transformer. Jerry
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16th May 2022, 9:06 pm | #5 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,820
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Re: AC/ DC radios live chassis.
Lots of useful info here: https://www.vintage-radio.com/repair...ly-stages.html
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17th May 2022, 12:48 am | #6 | |
Dekatron
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
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Re: AC/ DC radios live chassis.
Quote:
As for switching, the best method is a single pole switch in the LIVE only, with the neutral permanently hard wired to chassis for best safety. |
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17th May 2022, 10:19 am | #7 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,820
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Re: AC/ DC radios live chassis.
Or simply switch off by pulling out the mains plug, which also saves wear and tear on the radio's mains switch and volume/tone pot if they're combined with it.
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17th May 2022, 10:39 am | #8 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: AC/ DC radios live chassis.
With the mains Neutral connected to/switched through to chassis a Neutral interrupt could surprise the unwary
Lawrence. |
17th May 2022, 11:10 am | #9 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
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Re: AC/ DC radios live chassis.
It was somewhat normal for the switch to be in the neutral wire though, because this means that when the radio is switched on the power wiring adjacent to the volume control wiring is at chassis potential, meaning less chance of AC hum getting across and into the audio circuit.
Putting the switch in the live wire means you have 250Volts passing rather close to the volume control..
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17th May 2022, 11:21 am | #10 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,820
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Re: AC/ DC radios live chassis.
Yes, I have several AC/DC sets where the switch is single-pole and in the neutral/chassis connection, e.g. Roberts P5A.
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17th May 2022, 1:27 pm | #11 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
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Re: AC/ DC radios live chassis.
In the days when 2 pin plugs, or a BC adaptor in a light socket, were commonly used to power domestic appliances, it was a 50:50 chance which conductor would be "hot".
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17th May 2022, 5:24 pm | #12 | |
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 823
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Re: AC/ DC radios live chassis.
Quote:
Most of the radios exported to 220/240 volt countries, generally were the inexpensive makes using a resistive mains lead, which isn't very impressive. Our listing agencies, such as U/L would not approve this design. Dave, USradcoll1. |
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17th May 2022, 5:59 pm | #13 |
Hexode
Join Date: Oct 2012
Location: London, UK.
Posts: 497
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Re: AC/ DC radios live chassis.
With radios with a line cord (resistive dropper in the lead) the switch has to go in the neutral.
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18th May 2022, 9:53 am | #14 |
Octode
Join Date: Jul 2009
Location: Carmel, Llannerchymedd, Anglesey, UK.
Posts: 1,497
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Re: AC/ DC radios live chassis.
Indeed. In my apprentice days, i was advised to see if the chassis was live by gently drawing the back of the hand across it and detecting a 'buzz'!
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18th May 2022, 11:38 am | #15 | |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
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Re: AC/ DC radios live chassis.
Quote:
Most line cords were simply a resistor in series with the whole set, at any rate for US imports. The position of a switch in a simple series circuit has no effect on its switching function. There were some UK designs with tapped line cords which allowed higher HT voltage to which this could apply I guess though a single switch in the heater feed branch would still work and would have the advantage of leaving the chassis at neutral with fewer parts still live than with switched neutral. And no worse off than any other AC/DC with reversed mains in and single pole switching either.
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18th May 2022, 5:31 pm | #16 | ||
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 823
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Re: AC/ DC radios live chassis.
Quote:
Dave, USradcoll1 |
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18th May 2022, 6:05 pm | #17 |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 2,129
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Re: AC/ DC radios live chassis.
Yes, the neutral side of the AC mains should go to chassis.
With DC mains, the user got no choice, and with non polarised plugs on AC it was pot luck. But these days with DC mains being effectively extinct, and polarised plugs being almost universal, then neutral to chassis. For best safety turn the set off at the socket outlet when not being used. |
18th May 2022, 8:52 pm | #18 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,548
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Re: AC/ DC radios live chassis.
They can't be that unsafe! TV's used the same technology for a lot longer and I repaired hundreds of them without the hint of any danger. The workshop I started in didn't have isolation transformers and the benches were fitted with two-pin plugs so worked on the sets (radio's and TV's) on raw mains. All I did was check the chassis with a neon screwdriver to see if it was live or not.
An isolation transformer doesn't really make the sets safer. You can still get a nasty belt if you touch anything live. All the transformer does is enable you to connect earthed test equipment.
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19th May 2022, 9:53 am | #19 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: AC/ DC radios live chassis.
Re: Isolating transformer, see Post#8.
Lawrence. |
19th May 2022, 10:03 am | #20 | |
Nonode
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
Posts: 2,965
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Re: AC/ DC radios live chassis.
Quote:
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