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 Post subject: Chassis Material
PostPosted: 02 Aug 2010, 18:55 
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Joined: 07 Feb 2010, 15:42
Posts: 151
Location: England
Hi everyone,

Wanting to build a set of Oddblocks but before I begin to plan everything out I first need to decide on which material to use. I would very much Like to use MDF, its easy(ish) to work with, and I can sand it down, paint it and lacquer it so it has a nice piano finish. But my only concern is how does MDF react to being subjected to heat given off by vacuum tubes and having big heavy 11lb output transformers sat on top of it?

I definitely don't want to use a metal chassis, not only would I find this a pain to work with but I refuse to fall into the trap of a bog standard hammond chassis with some glowing glass and big transformers at the back, so if MDF is unsuitable on its own could someone suggest how I could make it work.

The chassis style I was aiming for was something like this:
Image
BUT without all the outlandish controls and the gawd awful thick grid on the front, just the general flat bottom with a cover going over the top, in some sort of bright colour. Along with the amplifier section I'd have another box of similar dimensions and style to house the power transformers and their caps etc. so they are isolated from the valves and OPT's.

In short can MDF handle heat?

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 Post subject: Re: Chassis Material
PostPosted: 03 Aug 2010, 12:11 
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Joined: 28 May 2008, 21:53
Posts: 4579
Location: Winnipeg, CANADA
I don't like using wood as an electrical chassis as is does not provide any electrical shielding.

This is from Pete's SE 813 build
I built the amp chassis out of MDF. I would not encourage you to do this, though - the MDF traps too much heat. I started off by trying small fans to move air through the box, but it was too noisy. I finally went with a perforated bottom, and added air holes along the sides of the box. Even so, it gets hotter inside than I'd like. In fact, that's why I added the temperature sensor to the micro, to be able to shut down if it gets too hot in there.

Since MDF is made out of wood waste fibers glued together with resin, heat, and pressure I would not expect it to fall apart with heat below the combustion temperature.
Cheers

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 Post subject: Re: Chassis Material
PostPosted: 03 Aug 2010, 12:58 
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Joined: 24 Jun 2010, 00:48
Posts: 788
Location: Christchurch, NZ
I would not suggest MDF as the resins are unstable with applied heat. Here in Malaysia, I have a few panels of MDF that have fungus growing on them due to the excess humidity when they are left in the garage ! I would suggest spray painting the MDF panels even on the inside surface or using some kind of coat to protect the bare MDF panel.

HOwever you might be able to pull it off by using a combination of PCB's and aluminium parts(sheets) to contain the elements which conduct a lot of heat, while being able to paint/finish the MDF panels for aesthetics. This will be a challenge.

For example power tranny on a small sheet of aluminium inside the MDF enclosure.
Valves on PCB and within 1 inch from the MDF board. (Raised PCB boards perhaps?)
Ventilate the box thoroughly ! =)
Oh, and hope ya have a fire extinguisher nearby just in case :D :D :mrgreen:

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 Post subject: Re: Chassis Material
PostPosted: 03 Aug 2010, 16:13 
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Joined: 07 Feb 2010, 15:42
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Location: England
How about some sort of metal sheet to line the inside of the case, surely if it was polished it would radiate heat back into the amp rather than into the actual board?

Ill try to make some 3D models of what I am trying to achieve, to be honest it doesn't look too much like that head amp.

Ill post them tomorrow or early morning :P

Lewis

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 Post subject: Re: Chassis Material
PostPosted: 03 Aug 2010, 17:26 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
MDF is quite common for head amps for guitars. Aluminum tape is often used.
http://www.tubedepot.com/p-tape-alum.html
In the second photo on that page you can see MDF being used for a tube guitar amp.

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 Post subject: Re: Chassis Material
PostPosted: 08 Aug 2010, 09:02 
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Joined: 07 Feb 2010, 15:42
Posts: 151
Location: England
Finally sat down with sketchup and threw a model together quickly :

Image

As you can see, its just a plain flat base with the tubes and OPT's but then it has a cover that sits over the top, I would then possibly have a panel of transparent material such as speaker grille that I could take off as and when I want to hide the stuff on the inside. I would leave the back open and unblocked, of course this doesn't include things such as space for the board (I'm thinking a turret board with the tubes mounted on turret board mounts http://www.hificollective.co.uk/images/b9avalvel.jpg ) and output and input connectors.

All I want to know is will this catch fire, I wouldn't run it constantly and I would always 'supervise' it so it wont be unattended :firefighter:

I might yet just get a pen and paper and do a proper tech drawing with accurate valve sizes etc. I suppose it would give a better representation

Thanks for any comments

Lewis

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 Post subject: Re: Chassis Material
PostPosted: 09 Aug 2010, 14:21 
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I would be worried about using something like a fabric speaker grill. How about some sort of metal grill? It will let air pass and is not flammable like a fabric.

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 Post subject: Re: Chassis Material
PostPosted: 31 Jul 2011, 20:38 
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Joined: 26 Oct 2008, 13:48
Posts: 70
Location: Central California coast
Wood enclosures were used all the time back in the days of tube radios. Most of the table radios didn't even have vent holes! Radio tubes don't dissipate as much heat as power tubes though.

I'm buildig a 7695 SE stereo amp and I've put it in a wood enclosure. I have added vent holes in the bottom that use the chimney affect to bring ambiant air up through the aluminum chassis past the 7695s, then out the back through a perforated back panel. I may add a thin aluminum panel above the tubes to sheild the wood directly above if I notice any repercussions from the heat. I've used aluminum coated duct tape as a sheild, but the glue comes unglued with time.

You can add holes in the top, but that looks bad. You could try holes along the top of the sides. One thing to do for sure is to leave plenty of space above the PA tubes. Guitar amps use wood enclosures all the time too. Check out what they do to ward off the heat.

Good luck and good listening,


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