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Old 31st Mar 2014, 7:43 pm   #61
Boom
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

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one day I went to shut the window while my other hand was on the radiator.
One of the first things I learnt was to keep one hand in my pocket wherever possible. It is life saving advice.
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Old 31st Mar 2014, 9:04 pm   #62
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

I was told when working on domestic electrics to short out the wires before proceeeding, a bang may result, only a bang, no electocution.
 
Old 31st Mar 2014, 9:09 pm   #63
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

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I was told when working on domestic electrics to short out the wires before proceeeding, a bang may result, only a bang, no electocution.
It depends where you short them.
If you did it on the incoming supply in the breaker board. I think you would get a nasty surprise!

There are no shortcuts to testing with a meter.
Its like saying neutral is close to earth yes it is unless the return path is open. Then its live.

The 17th Ed has some very strange changes. The ring main is probably on its way out. Reason is if it goes open then it still works however the cable is now underrated and clearance times will be effected.

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Last edited by Tubeglow; 31st Mar 2014 at 9:16 pm.
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Old 31st Mar 2014, 10:13 pm   #64
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

If you are going to discharge a capacitor its better to make up a discharge lead that creates a controlled discharge. Now the level of control is dependant upon supply on the PSU this is another good reason to have a dedicated discharge resistor on the power supply.

Shorting out a capacitor is not a good idea and can damage the dielectric on the capacitor. NB old electrolytic capacitors may not have blow out protection and this can lead to some quite dramatic failures. (don't put your face over the top of the cap)

NB this is a modern one with pressure relief.

http://www.youtube.com/watch?v=TbvNLoZMDtg

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Old 31st Mar 2014, 10:24 pm   #65
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

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If you did it on the incoming supply in the breaker board. I think you would get a nasty surprise!
Beats a fatal shock anyday!
 
Old 31st Mar 2014, 10:29 pm   #66
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

What if your neutral is open and it doesn't go bang but its still live?
Great isn't it what if scenarios at the end of the day if you test for dead correctly it can't be live.

Test for dead:

Test the tester,
Test the supply is live, this proves the earth and neutral is good.
Isolate the supply,
Test between all phases and earth /neutral.
Test the tester on a known supply.
System is dead.

Ok if you now want to short the supply..fine.

PSU test for dead is the same.

Test the tester by measuring the supply.
Power off (if you want watch it bleed down)

Test the tester again on a supply..why because when the tester reads 0V it might be broken. A test on a known supply proves the 0V is true.

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Last edited by Tubeglow; 31st Mar 2014 at 10:48 pm.
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Old 31st Mar 2014, 10:48 pm   #67
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

As I mentioned earlier the single most mitigating factor is COMMON SENSE. Those that have it will appreciate the risks and the possible dangers. Those that don't will act irresponsibly and without thought for the consequences.

As far as a hobbyist approach to vintage equipment restoration is concerned there should, without being totally pessimistic about life, always be people that HAVE common sense and would, therefore, consider the hobby as a practical objective.
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Old 1st Apr 2014, 7:31 am   #68
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

Just a quick thought linked to test for dead.

Regarding RCD(earth leakage trips)in fuse boards.

If you test with your tester from live to neutral its OK.

If you test from live to earth or neutral to earth it might operate the RCD.
Its not a problem because if it operated the circuit will be dead.(however you will have to reset all the clocks etc)
Remember this is relevant, because your project is connected to the mains supply.

I wasn't going to mention it, however its better to know.

The Phase (live) to neutral test still proves the neutral is good. (and will not operate an RCD equal current in supply and return.)


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Old 1st Apr 2014, 10:25 am   #69
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

One other survival-technique I learned early on was when working on HV capacitors used for motor-start circuits, fluorescent tube ballasts, power-factor-correctors in industrial applications - store the spares with their terminals shorted.

If you test a big capacitor and after the test it appears to be discharged you can put it back on the shelf then if you test the voltage across the terminals (or touch them!) a few days later you may be surprised.

Quote:
Originally Posted by Tubeglow View Post
If you are going to discharge a capacitor its better to make up a discharge lead that creates a controlled discharge. Now the level of control is dependant upon supply on the PSU this is another good reason to have a dedicated discharge resistor on the power supply.
That's SOP in commercial high power transmitters: they have a supplied "discharge wand" in the cabinet - basically a long insulated stick with a metal ball on the end, connected via a flexible cable and a limiting resistor.

Even though the TX has interlocks that are supposed to knock the power off if you remove the access covers, procedure requires you to touch a number of 'hot' points on the internals of the transmitter before beginning work on it to make sure there's no HV still there.

Some installations even have a clip on a HV part of the equipment to which you clip the discharge wand while you're working - so providing a positive visual indication that the HT is grounded, and to provide some safety inthe event that someone else powers the kit up while you're working onit.

[That should _NEVER_ happen: if working in a multi-operator environment you should "Lock-out, Tag-out" so nobody else can power up what you're working on]

http://en.wikipedia.org/wiki/Lockout-tagout
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Old 1st Apr 2014, 11:01 am   #70
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

Reminds me off that TTT about electrical safety, S.I.D.E., Switch off, Isolate, Dump, Earth.
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Old 1st Apr 2014, 11:04 am   #71
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

This is reminiscent of my training as a RADAR mechanic many years ago. The EHT cabinets had such a wand. There were interlocks and auto discharge devices but we were told - never assume they work. Discharge with the wand before touching anything and then leave it there.

I never discovered whether it was for real, or just window dressing, but on the first day before the first lecture, an ambulance with flashing light drove away from the Radar Trailer. As a result I never saw anyone taking liberties with HT during the whole course.
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Old 1st Apr 2014, 1:40 pm   #72
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

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If you test a big capacitor and after the test it appears to be discharged you can put it back on the shelf then if you test the voltage across the terminals (or touch them!) a few days later you may be surprised.
Dielectric absorption,

Great isn't it "its dead" well that's the theory..

That was the one (LOTO- fancy a gamble? Would you gamble your life on it?) LOTO lock out tag out!

I remember once after test for dead on an installation no one had worked on before, three of us looking at each other then one said OK who's going to be first to touch it then?

about a minute later shall we test it again?
OK
A minute later well who's going to touch it then..

Tubeglow.

Last edited by Tubeglow; 1st Apr 2014 at 2:08 pm.
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Old 2nd Apr 2014, 8:56 pm   #73
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

The forward in my former employer's safety instructions said " The price of freedom is eternal vigilance. The price of safety is the same" Good advice..
Part of the problem today, I think is that skills, training and experience are no longer required to fix faults (Open door, look for the module with the red light, replace said module with spare, look for row of green lights, lock door and take faulty module back to base). Once you take skill etc. out of the equation, the equipment must be made intrinsically safe, and the concept of danger associated with electricity disappears.
When I started work in the early 60's there were still a number of open 415 switchboards in use, with just a wooden handrail to prevent the unwary from accidental contact. What prevented accidents was training and tight operational disciplines. Not sufficient in these days of risk assessment. On a personal note, I confess I'd forgotten that a 90v battery can give you quite a surprise if you are not vigilant about where you place your fingers!!
See attached picture of 415v switchboard. decommissioned in 1985.
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Old 3rd Apr 2014, 9:26 am   #74
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

Mmm, I think that would even frighten me!
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Old 3rd Apr 2014, 10:23 am   #75
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

What a marvellous thing. But don't trip on your shoe-laces...
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Old 3rd Apr 2014, 10:40 am   #76
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

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Lets all stay cheerful and use an isolation transformer.
I am not sure if this has been discussed on here before, but be careful you don't become complacent and expect an isolation transformer, or an earth trip for that matter, to protect you from serious shock.
I learnt the hard way and suffered a sustained 240v AC shock. I was working on a mains battery valve portable, and turned the innocent looking set over to measure a voltage point on the other side. As I turned it over my left hand came into contact with the exposed mains dropper on the other side, and as I had the set in both hands the resultant shock went from hand to hand, up the arms and across the shoulders. My muscles locked up and I gripped the radio chassis harder and harder. I could not let go and could not make my arms move to hit my isolation switch. I stood up still gripping the chassis and screaming, after about 6 or so seconds my arms came closer to my chest and when the chassis touched my bare chest (it was a hot day) I think this reduced the current in my right arm releasing my grip in the right hand and the chassis dropped to the floor, and I fell back into my chair. By this time my wife had arrived at the top of the stairs and came into the room to see what the commotion was. Her first words were what is that awful smell of burning. My flesh I replied.
The skin on my left hand had been cauterised for an area of about 15mm by 20mm, the terminal on the dropper resistor had pierced the skin and left a charred hole in my hand about 5mm deep.
It took over 4 months for the wound to heal over fully.

The earth trip did not operate because the shock was from live to neutral. Neither would an isolation transformer have prevented the shock.

Please remember YOUR safety comes first, and dont pick up a chassis when it is connected to the mains.
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Old 3rd Apr 2014, 11:05 am   #77
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

That's absolutely horrific! I bet those 6 seconds felt like a year. Glad no lasting damage was done. Just goes to show, accidents can happen even to those of us who know what we're doing.
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Old 3rd Apr 2014, 11:18 am   #78
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

There's a very graphic reminder that electricity has no friends and is always looking for a way to take a bite! I've had quite a few belts over the years but the worst injury has only been a small white spot burn on a thumb or finger, I would not want to suffer as in this example!
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Old 3rd Apr 2014, 12:43 pm   #79
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Default Re: Is Practical Vintage Radio Too Dangerous For The 21st Century?

"Is Practical Vintage Radio Too Dangerous For The 21st Century?"

I'd say No, with due care and vigilance (I don't envy Crackle's experience above).

But Practical Vintage TV? Yes - probably too dangerous for ANY century in fact. Hence the development of flyback-EHT.
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