Wooden Chassis - problems?

[snowballfight]

Hi guys,

I am making a preamp design with three small tubes and reasonably small transformer.

I don't have the tools with me to make the chassis out of metal, especially from scratch, whilst I'm at home. Being a mech eng university student, during term time I have access to all the right stuff but... it's closed for now. What I CAN do is make it out of wood, obviously with a very simple design. Probably a glorious mix of sheet wood, glue and nails (well hidden of couse!). I guess the purpose of this would be just to form a layout to use later, and hold the transformer/tubes upright and off the ground. A simple front plate for holding the pots and jacks etc would be nice.

Anyways, I have questions relating to the grounding of such a system.

In theory, I'm trying to use a star system working off each of the shunt capacitors of the PT circuit, traveling to a distant star and then direct connection to the chassis. But this of course doesn't work with wood lol would I therefore connect this directly to the main grounding line?

Also, how would I treat the pot and jack grounding loops since I want to keep the two separate just for good practice, if I can. Will connecting these two loops directly to the mains avoid hum issues?

Finally, with mains, 266V @ 80mA and 6.3V @ 3A, should I be worried of things such as wood charring etc? and also sufficient/safe capacitor dissipation (this is what I'm really scared about! :P)? How can I make sure I won't shock myself into oblivion!

Thanks!

[Bruce / Mission Amps]

Well I'm sure you could figure out how to do this but I wouldn't waste my time with that.
There are obvious reasons a well grounded metal chassis is the norm... and it is more likely to be the 120v, 220v or 240v mains being the part that will hurt or kill you in a poorly constructed electronics project.
It would be very cheap to find or get a metal chassis anyhow, you don't have to make one.
You can find old chassis' or old radios and stuff all over Ebay ... or even scrounging through your neighborhood on trash day can produce a usable chassis.

[snowballfight]

Yeah well the problem is that for the life of me I can't find even a medium sized 2 pre tubes/1 power tube chassis, let alone a 3 pre tube one on the internet. Its a weird ask I presume. What alternatives could I look for? I'm in london so all that kind of trash goes to the large dumps straight out. I might be able to look through them, but needle in a haystack!

[bob p]

I commonly see DIY HiFi amps that are made out of wooden chassis. Its become an affectation in the HiFi crowd. Although people claim to be doing it for cosmetic reasons, I personally think they do it because they lack metalworking skills. It would be OK to build a wooden box around a metal chassis, but I think that an all wooden chassis is just a bad design.

The only problem that I can imagine in DIY'ing an aluminum chassis is cutting proper holes. To do it right you need Greenlee punches, but many people get by with a stepper drill bit.

[Memphis]

Snowball, check your pm's.

Bruce

[paggerman]

chassis alternatives

Hi guys,

I am making a preamp design with three small tubes and reasonably small transformer.

I don't have the tools with me to make the chassis out of metal, especially from scratch, whilst I'm at home. Being a mech eng university student, during term time I have access to all the right stuff but... it's closed for now. What I CAN do is make it out of wood, obviously with a very simple design. Probably a glorious mix of sheet wood, glue and nails (well hidden of couse!). I guess the purpose of this would be just to form a layout to use later, and hold the transformer/tubes upright and off the ground. A simple front plate for holding the pots and jacks etc would be nice.

Anyways, I have questions relating to the grounding of such a system.

In theory, I'm trying to use a star system working off each of the shunt capacitors of the PT circuit, traveling to a distant star and then direct connection to the chassis. But this of course doesn't work with wood lol would I therefore connect this directly to the main grounding line?

Also, how would I treat the pot and jack grounding loops since I want to keep the two separate just for good practice, if I can. Will connecting these two loops directly to the mains avoid hum issues?

Finally, with mains, 266V @ 80mA and 6.3V @ 3A, should I be worried of things such as wood charring etc? and also sufficient/safe capacitor dissipation (this is what I'm really scared about! :P)? How can I make sure I won't shock myself into oblivion!

Thanks!

My first build used a stainless steel Ikea roasting tin. I would strongly recommend NOT using SS as chassis as it is really hard to drill. However, there's nothing wrong with using a non-stick roasting pan as it is easy to drill/cut and they're cheap.

[olddawg]

Find an appropriate size piece of sheet steel, copper, or aluminum. Recycle something if you can. (Hint the bottom of an old VCR or stereo works nicely) Use a couple of 1x2 boards and some C clamps to cleanly bend a front and back panel. Drill your holes and mount it in a box. Sreiously though. If you can find a chassis to strip and re-use it would be easier. You can usually find some dead piece of solid state junk for nothing.

[tedmich]

some beautiful wooden boxes can serve as fine amp chassis if you make a Faraday cage internally. A sheet of conductive metal foil around the inside does this, like a single sheet heavy duty Reynolds Al foil or even a bunch of 3M Cu tape, some even use the conductive paint seen in guitar cavity shielding. A local sheet metal shop will toss off a bent Al form for quite cheap too!

[J M Fahey]

I have not been in London for many years now, but I remember that street (do no remember its name) where you can find *many* electronics shops, with big surplus/trash/obsolete/junk bins at their doors, where you will certainly find something useful.
Otherwise, access to a vertical drill (or a hand one mounted on a stand), a couple drills plus a 19mm circular saw for noval sockets will give you awesome hole-making power.
A friend of mine made an excellent sounding AX84 amplifier on an aluminum baking pan, very strong (one piece stamped construction) , light, and relatively easy to work with.

[Dave H]

I have not been in London for many years now, but I remember that street (do no remember its name) where you can find *many* electronics shops, with big surplus/trash/obsolete/junk bins at their doors, where you will certainly find something useful.

Was that the Edgware Road?

I'd just use one of the bigger diecast boxes as they are easy to drill. You should be able to find one down the Edgware Road. If not RS, Farnell and Bluebell Audio have them.

[J M Fahey]

Was that the Edgware Road?

That's the one.
Agree with the diecast box suggestion, because it's actually easier to drill than sheet aluminum.
An alloy that's meant to be cast is relatively hard and brittle and easier to cut while sheet aluminum is pure and soft and clings to the tool edge.