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Old 7th March 2004, 10:21 AM   #1
jim is offline jim  Belgium
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Default Enclosures in MDF.

Hi all,
Anyone ever tried an amplifier enclosure made of MDF with small metal plates on top for holding the tube-sockets ?
I'd like to try this because MDF is so easy to work with.
I could even veneer the MDF.

Any recommendations ?
Thanks,
Jim
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Old 7th March 2004, 11:45 AM   #2
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I am not a wood worker and I usually scab something together as a proto design. I have been known to use about anything for the base but I always use a full metal top in which to mount all the transformers,chokes, tube bases, and caps(if the can type). I am not a believer in mounting anything electrical to wood. This however is just my opinion and one that is probably not shared by others.

Joe
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Old 7th March 2004, 12:26 PM   #3
EC8010 is offline EC8010  United Kingdom
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If you mount valve bases on small metal plates, then mount them on MDF, you will create a safety hazard.

Very briefly. Electrical equipment must have two independent barriers between high voltages and you, the user. You can either have two layers of insulation (like the sheath and inner insulation on a mains lead), or a conductive layer firmly bonded to earth that totally encloses the high voltages (the second layer is the internal insulation between the high voltages and the chassis, and may be air).

As you can see, your proposed scheme does not meet either of the preceding criteria. Worse, MDF is wood-based, so it absorbs moisture, and its insulating qualities are questionable. The key point is that if you make something that causes your house to burn down, the insurance company will look very hard at the remains, and if they find that your equipment didn't meet safety requirements, they won't pay you. Of course, that might not be a problem, as you might already be dead.

The reason why ugly aluminium boxes are traditionally popular for DIY electronics is that it is easy to make them meet safety standards.
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Old 7th March 2004, 01:55 PM   #4
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I contruct my boxes for power supplies out of MDF, so basically they contain a traffo two bridges and a few caps. I cant see how this could be dangerous. Everything that needs to be earthed inside the box is and the amps chassis are earthed. There is no way that I can get an electric shock of the power supply boxes as none of them is metal. I cant get shocked off the amps because they are earthed.

The only danger with teh boxes is that they could catch on fire. But nothing ever gets hot enough to cause that, in the event of a problem im sure the fuses would blow, not only is each rail fused on the amp boards, but the secondaries and primaries are too. The plug has a fuse aswell.

If im in danger tell me please. If the only danger is that MDF is flammable then thats academic really as my monitor case is too. As are many other plastic casings on other equipment I have.
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Old 7th March 2004, 06:25 PM   #5
EC8010 is offline EC8010  United Kingdom
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It's more a legal/insurance issue than a direct safety issue. The courts don't understand physics and electricity (that's why they're lawyers). As a consequence, in the UK, there are very few laws explicitly about electrical safety. However, if you breach the Institute of Electrical Engineers' regulations, you will find that a court will hold you negligent for so doing, effectively making them law. In our modern litigious society, if a regulation is made, and a single person manages to injure themselves as a consequence, they could sue the regulatory body. Thus, regulatory bodies are very careful, and err on the side of caution. Insurers don't like to pay out on claims, so they stick to the letter of the regulations.

I'm not making a personal statement as to whether your use of MDF is safe or not, but I am saying that it doesn't meet common electrical practice, and if something did go wrong, you wouldn't stand an earthly in court...
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Old 7th March 2004, 06:42 PM   #6
sreten is offline sreten  United Kingdom
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JMO opinion but its more trouble than its worth.

Its a lot easier to use a flat metal plate combined with wooden sides.

If you can get hold off copper plate it looks nice also.

sreten.
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Old 7th March 2004, 06:54 PM   #7
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Lightbulb Check Out the Project Photos

Quote:
Anyone ever tried an amplifier enclosure made of MDF with small metal plates on top for holding the tube-sockets ?
Look through the projects photos (one of the permanent messages at the top of this forum), and you will see a project exactly as you describe--veneered and all!

It looks absolutely gorgeous, and the builder says it was a tremendous amount of work.

HTH.

Best,

George Ferguson
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Old 7th March 2004, 07:11 PM   #8
jim is offline jim  Belgium
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EC8010,

Quote:
If you mount valve bases on small metal plates, then mount them on MDF, you will create a safety hazard
And if you connect all the metal plates together with a wire and connect them to the earth wire ?

If you look at the photo project album, most of the projects don't meet the safety requirements you describe.

Greetz,
Jim
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Old 7th March 2004, 07:12 PM   #9
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Quote:
I contruct my boxes for power supplies out of MDF, so basically they contain a traffo two bridges and a few caps. I cant see how this could be dangerous. Everything that needs to be earthed inside the box is and the amps chassis are earthed. There is no way that I can get an electric shock of the power supply boxes as none of them is metal. I cant get shocked off the amps because they are earthed. The only danger with teh boxes is that they could catch on fire. But nothing ever gets hot enough to cause that, in the event of a problem im sure the fuses would blow, not only is each rail fused on the amp boards, but the secondaries and primaries are too. The plug has a fuse aswell. If im in danger tell me please. If the only danger is that MDF is flammable then thats academic really as my monitor case is too. As are many other plastic casings on other equipment I have.
I /think/ what they're trying to get at is that MDF collects moisture or holds enough for it to conduct between point-a to point-b so if your chassis earth becomes damaged like stepping on the power cord while active and neutral are both still sending power to the chassis-inside-an-mdf-box there is a chance that electricity will pass /through/ the MDF to something outside of the box, like carpet, or a cat lying next to your psu to keep warm or your foot...

You don't need a 'fire' inorder to start one, all you need is electricity to pass through a mildly moist or even dry wood to heat it up enough to 'ignite' it..

You are more than likely safe if the earth wire is going to the wall :P but that's one wire connected to one connector protecting you and everything else inside the chassis from meltdown...That isn't exactly redundant..

Just my 2cents
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Old 7th March 2004, 07:27 PM   #10
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by jim
And if you connect all the metal plates together with a wire and connect them to the earth wire?
Even if you do that. It's the use of MDF as the electrically insulating barrier that I'm concerned about. As sreten points out, you could use a single conductive top plate. Further, if you lined the inside of the wood with foil, and added a metal cover to the bottom, with all the metallic parts bonded to earth, then you would be OK.

Quote:
If you look at the photo project album, most of the projects don't meet the safety requirements you describe.
Um. Yes.

I believe that danger is a necessary part of life, and attempts to eliminate it are futile because it makes people less aware of remaining dangers. I regularly ride a bicycle. This is a machine that if it had been invented recently, would have been immediately outlawed because of the damage that can be done by the crossbar to delicate parts of the anatomy. As far as I'm concerned it's a useful machine, I'm aware of the danger and I avoid it.
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