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Old 8th May 2021, 12:56 pm   #1
DonaldStott
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Default Bush DAC10 - Live Chassis!

I've now restored a number of Bush DAC10 sets and have found on every occasion that the LIVE and NEUTRAL feeds seem to be connected 'incorrectly' - in my opinion of course.

Here is an extract from the circuit diagram clearly showing the NEUTRAL feed going via the lamps and R18 to the chassis while the LIVE feed goes to the top of the Dropper R17 :-

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In all the sets I have restored the connections are the other way round which, I think, would result in a LIVE chassis!

Am I missing something or is it just an artefact from the era of the two pin plug? It clearly doesn't matter to the DAC10 which way round these connections are but in the interests of safety it would seem appropriate to make the necessary adjustments?
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Old 8th May 2021, 1:11 pm   #2
ms660
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Default Re: Bush DAC10 - Live Chassis!

When connected correctly there's always the risk of a live chassis with the receiver connected to the mains.

Lawrence.
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Old 8th May 2021, 1:38 pm   #3
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Default Re: Bush DAC10 - Live Chassis!

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Originally Posted by DonaldStott View Post
Here is an extract from the circuit diagram clearly showing the NEUTRAL feed going via the lamps and R18 to the chassis while the LIVE feed goes to the top of the Dropper
How does it show that? All I can see are signs for AC and DC mains, this being an AC/DC set. When using the set on DC mains you'd have to try the plug both ways to find out which way worked.
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Old 8th May 2021, 2:08 pm   #4
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Default Re: Bush DAC10 - Live Chassis!

What you are saying then if I understand correctly is that the red wire of the mains lead connects to the switch and then having passed through the switch goes to chassis (via the lamps and shunt resistor) rather than to the dropper?
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Old 8th May 2021, 2:13 pm   #5
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Default Re: Bush DAC10 - Live Chassis!

That may well be the case, but it's not what the OP said.
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Old 8th May 2021, 2:39 pm   #6
DonaldStott
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Default Re: Bush DAC10 - Live Chassis!

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Originally Posted by slidertogrid View Post
What you are saying then if I understand correctly is that the red wire of the mains lead connects to the switch and then having passed through the switch goes to chassis (via the lamps and shunt resistor) rather than to the dropper?
In all the DAC10 sets I have restored this is indeed what I have found and is what I tried to articulate in my first Post above.

Does anyone use a DC mains supply these days?

With an AC mains supply, a properly connected switch and three pin plug it's not that difficult to avoid a LIVE chassis?

Don't want to stir up a hornet's nest so I'm satisfied with the responses and I know what I'm doing now ... as always my priorities are - safety - functionality - originality - in that order.
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Last edited by DonaldStott; 8th May 2021 at 2:49 pm.
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Old 8th May 2021, 2:44 pm   #7
slidertogrid
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Default Re: Bush DAC10 - Live Chassis!

I think the confusion on the circuit is that the AC symbol is being read as live and the DC symbol is being read as neutral.
To determine if it is wired incorrectly we need to know if the red wire of the mains lead goes to lamps/shunt/chassis or to the dropper.
I would expect to see the red wire going to the switch and then to the dropper and the black through the lamps to chassis.
I don't know of any mains supply which is DC now, not now everybody is on the grid.

Last edited by slidertogrid; 8th May 2021 at 2:47 pm. Reason: post crossed.
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Old 8th May 2021, 2:52 pm   #8
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Default Re: Bush DAC10 - Live Chassis!

Quote:
Originally Posted by DonaldStott View Post
With an AC mains supply, a properly connected switch and three pin plug it's not that difficult to avoid a LIVE chassis?
The best guarantee against a Live chassis is to use an isolating transformer.

With Live to dropper and Neutral to chassis all you need is a dirty switch contact or break and the chassis will reach a potential of 240 volts WRT Earth.

Remember that all circuits are potential dividers and that you don't want to become R2 so far as high voltages are concerned.

Stay safe.

Lawrence.
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Old 8th May 2021, 3:00 pm   #9
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Default Re: Bush DAC10 - Live Chassis!

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Originally Posted by slidertogrid View Post
I think the confusion on the circuit is that the AC symbol is being read as live and the DC symbol is being read as neutral.
Confusing live and neutral (AC mains supply) with positive and negative (DC supply of any type) is quite common. It may stem from the fact that UK mains leads once used red and black conductors. I'm not sure whether red would have indicated positive where DC mains supplies were used. Many sets used uncoloured figure of eight mains leads and when used on DC supplies the advice was to try the plug both ways.
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Old 8th May 2021, 5:00 pm   #10
DonaldStott
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Default Re: Bush DAC10 - Live Chassis!

No confusion here in relation to ' ... live and neutral (AC mains supply) with positive and negative (DC supply of any type) ...'!

In the set I am restoring I will have the AC Live running to the Dropper and the AC Neutral running to the chassis. And just to confuse lesser mortals like myself the wires on the set side of the switch running to the Dropper and the chassis are both RED!
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Old 8th May 2021, 5:08 pm   #11
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Default Re: Bush DAC10 - Live Chassis!

Making sure that the chassis is connected to mains neutral is a modern practice adopted in the interests of safety. When these sets were new no one cared and mains flexes were often uncoloured and single insulated.
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Old 8th May 2021, 5:30 pm   #12
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Default Re: Bush DAC10 - Live Chassis!

I see the same Graham, very odd statement.
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Old 8th May 2021, 8:51 pm   #13
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Default Re: Bush DAC10 - Live Chassis!

If the dc supply was positive earth, a non-live chassis wasn't even an option
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Old 8th May 2021, 10:02 pm   #14
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Default Re: Bush DAC10 - Live Chassis!

I prefer the chassis to go straight to neutral so I reposition the lamps and R18 to be in series between V4 and V5 heater circuit. The level of hum is reduced. I also recommend plastic sleeving on the lamp mounting.
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Old 9th May 2021, 4:34 am   #15
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Default Re: Bush DAC10 - Live Chassis!

I had to study the diagram several times to get my head around the bulbs arrangement, I've figured it out, the bulbs are wired inline with the return (I call neutral this because I'm a weirdo).
When restoring any sets like this, I use a multimeter to find out which way round the connector has to go to find the neutral line, the set has the back cover marked accordingly.
As Donald has already said, he likes to put the feed (live) to the dropper, this is the correct way to do it.
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Old 9th May 2021, 12:42 pm   #16
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Default Re: Bush DAC10 - Live Chassis!

I would always make sure the chassis was connected to neutral as this is by far the safest option. One thing I've never been able to get my head around is if you had DC mains and you were on the Positive main would that have to go to chassis or or to the dropper? Same question if you were on the negative main assuming the centre wire was earthed Dc mains is long gone from the UK but I believe in India it's only completely gone in the last few years
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Old 9th May 2021, 12:45 pm   #17
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Default Re: Bush DAC10 - Live Chassis!

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Originally Posted by kellymarie View Post
One thing I've never been able to get my head around is if you had DC mains and you were on the Positive main would that have to go to chassis or or to the dropper?
Think about how a diode works.

Lawrence.
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Old 9th May 2021, 1:25 pm   #18
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Default Re: Bush DAC10 - Live Chassis!

If I was wiring an old-colours 2-core mains lead to an AC/DC radio, I'd wire it so that on DC mains the black wire as the -ve and the red wire the +ve. Which coincidentally makes the black wire go to the chassis (possibly via dial lamps and the like) which makes sense for AC mains too.
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Old 9th May 2021, 1:37 pm   #19
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Default Re: Bush DAC10 - Live Chassis!

Yes, but as stated in post #13, if the DC supply was positive earth the chassis would be live wrt to earth.

There's no way of avoiding this.
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Old 9th May 2021, 4:14 pm   #20
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Default Re: Bush DAC10 - Live Chassis!

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Yes, but as stated in post #13, if the DC supply was positive earth the chassis would be live wrt to earth.

There's no way of avoiding this.
Sure, but at least the colours of the wires would indicate which had to be +ve for the set to work.

And there is a totally impractical way of avoiding a live chassis if you have a +ve earth DC supply. A motor-generator set or similar. No I am not seriously suggesting using one for this (how many people actually run an AC/DC radio on a DC supply nowadays?) but telling me that something is impossible is equvalent to asking me to find a way to do it.

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