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Old 17th September 2012, 04:39 PM   #1
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Default Wood chassis

Hello All,
I would like comments on the project I'm working on. I am building an 6BQ5
push/pull amp and I am making an all wood chassis. What pit-falls should I
look for?
For a little history on the amp, see post #72 here.

Anyone ever made the EL84 P-P circuit referenced on the Tubecad Journal site?

Thanks.
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Old 17th September 2012, 05:30 PM   #2
DF96 is offline DF96  England
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Hum (from heaters), buzz (from PSU), RF interference (from everywhere). These problems can be overcome but it is harder because you have no convenient metal screen.
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Old 17th September 2012, 05:45 PM   #3
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Hello Bruce,
A totally wooden chassis is a nifty way of making an amp since, I like wood. And aside from the lack of any shielding that a metal chassis would provide, I still like the idea and may do one myself if I live long enought to get around to it. But I can think of one thing.

If I were making this, I would provide for a safty ground system below the wood top plate just as there would be with a metal chassis. Perhaps a wide piece of sheet copper below the transformers. That is, one wide enough to span all three transformers with appropriate holes for both the wires and all the mounting bolts. I'd make sure that at least one bolt of each transformer made a good and proper contact with the metal end shell by removing some paint from the mounting foot. Then this collective ground connection would connect to the mains third wire ground.

If a copper sheet is not to your liking, then I suppose aluminum would work too. Or even a heavy solid copper buss wire connecting each transformer from below, and grounding it, would serve the same purpose. Remember it's for safety reasons incase a transformer develops leakage, or even a short to the core. Doesn't happen often, but it could.
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Old 17th September 2012, 05:49 PM   #4
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I'd cover the insides with blank PCB for shielding.
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Old 17th September 2012, 06:00 PM   #5
M Gregg is offline M Gregg  United Kingdom
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Hi,

Just for interest, They work great this one is silent
Its been posted before, I use double sided PCB and aluminium foil.
Just use all the usual twisted heaters etc.
Remember to earth your transformers and all metal parts..Thats why I used a ground plane.

So you could cover the inside of the top with pcb, just take precautions for eddy currents and if you take an AC cable through the ground plane bring the return back though the same hole. Cut any holes and slit the copper to the outside of the board. I prefer wood chassis



Regards
M. Gregg
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Old 17th September 2012, 07:00 PM   #6
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Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
Aluminium chassis' have virtually no shielding effect, almost transparent to EM fields. Substances can be either reflective or absorptive to EM....The trick way is to make a two layered chassis....copper on the inside to absorb EM and Stainless Steel on the outside to reflect EM....what EM gets thru the copper reflects off the SS to make a second pass thru the copper.


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Old 17th September 2012, 08:55 PM   #7
DF96 is offline DF96  England
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Thin aluminium has a huge shielding effect for electric fields, but little for low frequency magnetic fields. Any metal (any good conductor, in fact) will do this for electric fields.

To absorb 'EM' you don't use copper but a resistive material which matches the impedance of free space. Copper reflects 'EM' very efficiently. Stainless steel possibly slightly less so as it is not quite such a good conductor.
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Old 17th September 2012, 09:04 PM   #8
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You can try what I'm doing with a tube preamp right now. I'm using a cake pan as a subchassis and building it into a wood enclosure. It's similar to what HollowState describes.

Sorry, no pics yet.
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Old 17th September 2012, 09:21 PM   #9
disco is offline disco  Netherlands
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Depending on circumstances your hifi might suffer from the reception of signals. Most coming from radiostations, cell phones, computers and energy saving light bulbs. Despite all theory there's no need shielding your case with metal as the tubes themselves are sticking out. Neither thin steel, aluminium or copper is preventing 50 or 100Hz magnetic fields to pass. Wood is a good material for building an AF amplifier case. Just take care of disturbing signals and limit the bandwith to frequencies of interest.
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Old 17th September 2012, 09:24 PM   #10
tomlang is offline tomlang  United States
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Timely thread. This build is a remote controlled tube preamp. I used my Shopbot CNC to machine a plywood chassis to fit inside an empty Eico metal amp enclosure. I was dreading painting it, worried about temperature issues, etc.

Then a light bulb went on -- use Corian. Corian scraps (especially the part cut out for the sink) can be aquired for cheap or free and machines even easier than wood.

This was pure white Corian. Now I want to get more "artistic" with an amp that looks like it was mounted on a "granite" chassis.
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