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Old 29th May 2003, 04:28 PM   #1
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Default Building tube amp in wooden box(es)

Hi,

I looked through the archives, but didn't see this addressed specifically. Is it feasible to build a tube amp in a completely wooden enclosure or enclosures? This may make more sense for a first-timer like me, for the following reasons:

* It's easier and cheaper to find wooden boxes than Hammond aluminum enclosures. I've seen 6"x9" cigar boxes selling on eBay for under $10, a pair of these should be enough real estate to build a stereo amp (monoblocks or separate PSU/audio sections).

* It's easier and cheaper to find tools that can cut holes in wood. I've seen hole saws on eBay for $10-$20. Granted, these probably wouldn't last beyond the first project, but for now, that's all I'm looking for. If I later decide to get into the hobby more seriously, I'll buy a proper set of tools.

* It'll be cool, and different from everyone else's amps

So I'm thinking of trying this with 2 wooden boxes, one for the PSU and one for the audio circuit. Monoblocks would cost more because I'd have to duplicate the PSU. Also, the only 17" wooden box I could find on eBay was a Smith & Wesson display box, and it was over $100

What would the potential problems with this idea be?

* Shielding. I'm not sure how much RFI there is in my environment. I've picked up talk radio once, when I was trying DIY tonearm cable and hadn't shielded it properly. However, that's a good 60dB below the level of the amp, and other than that I haven't directly experienced RFI, so maybe I'll be OK on that front. Is there any reliable way to find out how much RFI I'm dealing with?

* Heat. This is the next big issue in my mind. I know wood will catch fire at a lower temperature than aluminum Would a tube amp get hot enough to set a wooden chassis on fire? Should I drill ventilation holes around the tubes like I see in some amps? Should I add metal heatsinks for PS or cathode bias resistors?

* Bracing. This depends on how thin the wood is, I guess, but I would think that a cigar box would be able to handle a power transformer and choke, and the 125ESEs don't look too heavy.

* The umbilical. I'm aware of some of the issues involved here, because I built my (SS) phono stage as two boxes. That's a 45V supply, so I wasn't too careful with it, but for a tube amp, I know I'll need decent locking connectors, make sure the end connected to the PS is female to prevent accidental electrocution, shield HT from heater (or maybe even use 2 umbilicals and make sure they can't accidetally be cross-connected), and so on. However, these are issues with having separate PSU and audio boxes, they're not related to the boxes being made of wood, so I can worry about them later.

Anything else I'm missing?

Thanks in advance,
Saurav
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Old 29th May 2003, 04:41 PM   #2
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I build my amps on wooden chassis for exactly the same reasons you mentioned.

http://home.zonnet.nl/horneman/se6c41cpics.htm

I have no problems with RFI.. But you could solve an eventual rfi problem by shielding components..like caps and chokes.

An added benefit is that the rca plugs are not grounded on the chassis but everything is grounded via star earthing...no ground loops in my wooden amps.

At the back of my amp i just have a whole slot so there is natural convection..i.e. not heat problems.

Bracing..depending on the thickness of the wood...speaks for itself really...I use plywood just because it is easy to get...plywood does not have the same good looks as real wood.

Dhaen has some very good options for an umbilical. Sure he'll chip in.

Cheers,
Bas
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Old 29th May 2003, 04:47 PM   #3
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Wow, that's a great looking enclosure! Did you build it yourself, or did you put a pair of old boxes together?

> At the back of my amp i just have a whole slot so there is natural convection..i.e. not heat problems.

Could you explain that please, I couldn't see that in the pictures. I'll probably leave the bottom open like you have, that should help too, especially if I drill holes on the top surface for convection.
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Old 29th May 2003, 04:58 PM   #4
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Hi Saurav,

Built it myself. Just glued them all together nothing fancy...yet ;-)

See the third photo from the bottom...there is a slot stretching almost from the one side to the other.(actually quite hard to see ) .....at the bottom of that " transformer box" there are a couple of holes (you can see a couple of them" that let the heat "out" from the "bottom" part..

Quote:
leave the bottom open
yes good idea..no way the kids can lift it..can't even lift it myself..

Cheers,
Bas
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Old 29th May 2003, 05:06 PM   #5
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No kids or pets, so that's not an issue. I saw the holes, and I see the slot now, it's right under the hinged lid. I know I won't build my own box, because I'm worse at woodworking than at electronics.
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Old 29th May 2003, 05:13 PM   #6
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Here is another one just posted at the Audio Asylum..

http://www.audioasylum.com/forums/tu...ges/30979.html
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Old 29th May 2003, 05:20 PM   #7
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You're in the states right?

Apparently Bombay Company is quite good for getting a nice wooden box..

http://www.bombaycompany.com

Nice box on a special

http://www.bombaycompany.com/webapp/...-1&siteId=core

$29
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Old 29th May 2003, 05:23 PM   #8
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.
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Old 29th May 2003, 05:26 PM   #9
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Wink And this one for the PSU!

.
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File Type: jpg psu.jpg (59.1 KB, 1393 views)
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Old 29th May 2003, 05:33 PM   #10
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I'd seen that AA thread, didn't realize it was you. Thanks for the Bombay Company link (yes, I'm in the USA), I hadn't considered buying a box from a store because I'd assumed they'd all be too expensive. I've been looking around at thrift stores too for a while, but haven't seen anything promising.

This is the kind of stuff I was loking at:

http://cgi.ebay.com/ws/eBayISAPI.dll...76&category=12

http://cgi.ebay.com/ws/eBayISAPI.dll...category=11673

http://cgi.ebay.com/ws/eBayISAPI.dll...category=11673
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