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Old 20th Jun 2021, 2:27 pm   #61
ms660
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Default Re: Vintage Sears Silvertone radio safety question

According to the schematic I'm looking at, the switched side of the mains is connected to chassis via the loudspeaker field coil and a 0.2uf capacitor connected in series.

Lawrence.
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Old 20th Jun 2021, 2:46 pm   #62
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Default Re: Vintage Sears Silvertone radio safety question

I'm sure you're right Lawrence, I answered generically and didn't look at the schematic
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Old 20th Jun 2021, 2:49 pm   #63
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Default Re: Vintage Sears Silvertone radio safety question

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I'm sure you're right Lawrence, I answered generically and didn't look at the schematic
That system was used a lot in American AC/DC receivers, unlike over here

Lawrence.
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Old 20th Jun 2021, 2:52 pm   #64
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Default Re: Vintage Sears Silvertone radio safety question

Does that mean it is a shock hazard?
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Old 20th Jun 2021, 3:32 pm   #65
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Default Re: Vintage Sears Silvertone radio safety question

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Does that mean it is a shock hazard?
With respect to Earth there's always a shock risk with AC/DC/Live chassis receivers, the only way to reduce the risk to a minimum (apart from not using it at all) is to power the receiver via a proper mains isolating transformer designed for the purpose.

For instance, say a Live chassis design receiver had the mains Neutral connected to the chassis via a single pole on/off switch that was connected to mains Neutral or via one pole of a double pole on/off switch that was connected to mains Neutral and that the Neutral wire in the mains plug was connected to the Neutral pin and that your mains outlet socket was wired correctly you might think no problem at all......think again....if the Neutral circuit was suddenly interrupted for whatever reason the chassis would suddenly rise to a potential with respect to Earth that equals the mains voltage, that's because the chassis would then be connected to mains Live via the low impedance series heater circuit, such an interruption could be caused due to various reasons (not all listed here) such as an intermittent wire or terminal connection, plug to socket connection, and if the Neutral circuit was fused in the receiver then also a poor fuse holder connection or a tired fuse etc.

Lawrence.
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Old 20th Jun 2021, 3:32 pm   #66
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Default Re: Vintage Sears Silvertone radio safety question

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I'm sure you're right Lawrence, I answered generically and didn't look at the schematic
That system was used a lot in American AC/DC receivers, unlike over here

Lawrence.
That set does not have a hot chassis! It uses a floating B- line and the only connection to the chassis is through a .2mfd capacitor.
The ground or earth symbol is the only connections to the chassis.
Dave, USradcoll1.
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Old 20th Jun 2021, 3:40 pm   #67
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Default Re: Vintage Sears Silvertone radio safety question

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I'm sure you're right Lawrence, I answered generically and didn't look at the schematic
That system was used a lot in American AC/DC receivers, unlike over here

Lawrence.
That set does not have a hot chassis! It uses a floating B- line and the only connection to the chassis is through a .2mfd capacitor.
The ground or earth symbol is the only connections to the chassis.
Dave, USradcoll1.
Yes a floating HT-ve line was implied in my post, for the avoidance of any doubt the in that post was in reference to a lot of British designs.

Lawrence.
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Old 20th Jun 2021, 3:47 pm   #68
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Default Re: Vintage Sears Silvertone radio safety question

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Does that mean it is a shock hazard?
No hazard whatsoever as long as the set is operated with the cabinet, back cover and all the knobs are in place.
The transformer you bought is probably an auto-transformer, as most travel step-down transformers are, as small size and light weight are important but can handle a little more power.
Dave, USradcol1
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Old 20th Jun 2021, 3:48 pm   #69
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Default Re: Vintage Sears Silvertone radio safety question

Thanks Guys!

I have bought an autotransformer Damn.
Basically the only thing I am worried about is the chassis screws at the bottom of the case having the potential to be live and conductive even when the case is on.

Judging by your replies it will seem somewhat safe with a fused transformer and a RCD.
Can anyone explain what a floating B- line chassis is layman terms?

Thanks

Thanks again Dave given me piece of mind. All the knobs are there but say if one was to fall off would the metal sheath underneath be live ?
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Old 20th Jun 2021, 4:30 pm   #70
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Thanks Guys!

I have bought an autotransformer Damn.
Basically the only thing I am worried about is the chassis screws at the bottom of the case having the potential to be live and conductive even when the case is on.

Judging by your replies it will seem somewhat safe with a fused transformer and a RCD.
Can anyone explain what a floating B- line chassis is layman terms?

Thanks

Thanks again Dave given me piece of mind. All the knobs are there but say if one was to fall off would the metal sheath underneath be live ?
A floating B- means the B- is not directly tied to the chassis, but is connected through an isolating capacitor, a .2mfd. The chassis shouldn't be live even when using an auto-transformer!
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Old 20th Jun 2021, 4:43 pm   #71
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Default Re: Vintage Sears Silvertone radio safety question

Thank you all, Its been a great learning curve for me!
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Old 20th Jun 2021, 4:47 pm   #72
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Default Re: Vintage Sears Silvertone radio safety question

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Can anyone explain what a floating B- line chassis is layman terms?
In the context of AC/DC receivers of the type being discussed it means the HT-ve line in the receiver is not connected directly to chassis but connected to chassis via a capacitor, in the schematic for your receiver that capacitor is shown as having a value of 0.2uF, capacitors exhibit reactance, the reactance of a 0.2uF capacitor at 50Hz is approx. 15.91k (15,910 Ohms) that means that under certain conditions when using a 240 volt to 110 volt step down auto transformer a current of approx. 15mA is available to flow from chassis to Earth via whatever path, human or otherwise.

Lawrence.
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Old 20th Jun 2021, 6:06 pm   #73
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Default Re: Vintage Sears Silvertone radio safety question

But in normal operating conditions the 15mA shouldn't be there? Would a 30mA rcd still trip if one was to get shocked at that mA?

As the plug is not polarised will the electricity always go through the 0.2uf capacitor no matter which way it is plugged in?

I feel its fine and I am just getting very paranoid :P
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Old 20th Jun 2021, 7:10 pm   #74
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Default Re: Vintage Sears Silvertone radio safety question

Draw a simple schematic showing the current path, all should become clear, draw showing for both normal and possible fault conditions, do a drawing with Neutral routed through to chassis via any switch or fuse that's fitted in that line then do the same and the same analysis with the Live being routed through to chassis, in the receiver in question, under certain conditions being powered by your auto transformer a voltage that equals the mains supply voltage will be available between the chassis and Earth and the available current will be approx. 15mA, the amount of current that will flow will depend on the impedance between the chassis and Earth.

For a chassis that's connected in DC terms to one side of the mains then under certain conditions again there will be a voltage that equals the mains voltage between the chassis and Earth but in that case the available current will be much higher and if for some reason the RCD fails to trip then that available current at that voltage can kill.

Last time I tested an RCD with a fault current to Earth I think it tripped at somewhere around 22-25mA but don't quote me on that.

Remember that a fault condition is a normal condition gone wrong....

Lawrence.

Last edited by ms660; 20th Jun 2021 at 7:25 pm. Reason: typo
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Old 20th Jun 2021, 8:04 pm   #75
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Default Re: Vintage Sears Silvertone radio safety question

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Originally Posted by sweepthedog View Post
But in normal operating conditions the 15mA shouldn't be there? Would a 30mA rcd still trip if one was to get shocked at that mA?

As the plug is not polarised will the electricity always go through the 0.2uf capacitor no matter which way it is plugged in?

I feel its fine and I am just getting very paranoid :P
If you use a toaster at home you shouldn't have any qualms using this radio, which is the safer of the two.

Gabriel
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Old 20th Jun 2021, 8:10 pm   #76
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Default Re: Vintage Sears Silvertone radio safety question

Haha thanks guys, when I get it setup I'll send a video here see it in its full glory
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Old 20th Jun 2021, 9:13 pm   #77
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Default Re: Vintage Sears Silvertone radio safety question

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Having now tested reception in my garden I can confirm many stations are received.
Inside the house I could only really get R5 live, plus lots of buzzing interference from computers and various switched-mode converters. My Ravpower 3 port USB charger seemed the worst offender, although it was admittedly quite close - this obliterated the band.

A second test of the Silvertone at my parents house (larger garden, fields on 2 sides) showed at least 10 stations could be received loud and clear without external antenna with more coming in with a short wire antenna, no buzzing at all in this location.
My conclusion:
Nice compact and thermally efficient short superhet set, -best suited for rural areas /low tech households. Needs a conventional iron step down transformer to 110v
How much power does your MW stations transmit at?
In the US, the stations transmit at anywhere from 500 to 50KW, depending on the location. At night, the stronger ones reduce the power and change the antenna orientation to alter the signal pattern.
Dave, USradcoll1
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Old 20th Jun 2021, 9:40 pm   #78
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Default Re: Vintage Sears Silvertone radio safety question

Closest 'Main one' is Moorside edge in Northern England. Transmits 3 stations (5 live talk sport and absolute radio) between 200-400KW and the signal is easily heard as far up north as Scotland and as Far down as the Midlands.
Others are more local and can vary like the University of York transmits at very low KW

( https://ukfree.tv/transmitters/analo...rsity_Se622506 )

but can be detected quite far.

Chris got it set up to a transmitter that received a station from the Midlands.

I would love to receive a Irish or continental station just for my own interest haha.
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Old 21st Jun 2021, 6:14 pm   #79
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Default Re: Vintage Sears Silvertone radio safety question

Radio arrives and works fine especially one on station!
Wish it would let me send a video but I'm really happy with it!
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Old 21st Jun 2021, 7:27 pm   #80
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Default Re: Vintage Sears Silvertone radio safety question

Matthew sent me the videos by email. I've uploaded them to YouTube.

Please enjoy responsibly

https://youtu.be/ZhaOEE5-IOA
https://youtu.be/iBRK0vAE7ug

Gabriel

Last edited by Gabe001; 21st Jun 2021 at 7:36 pm.
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