Dumb question?

[msmpe]

This may be a dumb question, but I haven't a clue as to the answer.

Why do we always use a metal chassis?
Why not use wood or fiber board or plexi or whatever? My breadboard is plexi and it seems to work just fine. My question is electronic, not the ease of working the material (the plexi was tough to work especially compared to aluminum).

Thanx

[20to20]

This may be a dumb question, but I haven't a clue as to the answer.

Why do we always use a metal chassis?
Why not use wood or fiber board or plexi or whatever? My breadboard is plexi and it seems to work just fine. My question is electronic, not the ease of working the material (the plexi was tough to work especially compared to aluminum).

Thanx

A few reasons at the top of the list would be...

Strength, for carrying transformers, and for pushing and pulling on tube sockets.

Because the holes for the screws that mount the sockets are usually very close to the socket holes there is very little material to provide strength for long term socket stability...

Ready made ground returns. Electrical shielding. Heat sinking properties. Heat shielding properties. Fire safety.


20

[DeathRex]

1/4 acrylic would work fine, and shouldn't melt. Everything should mount just fine, but you might need a ground to the transformers, coils, and volume pot.

[Tubeamp]

Exactly, I agree with what DeathRex said...probably you will need to run a ground wire on metal parts of the various components....so better to use a metal chassis instead.

[soundbrigade]

A compromise is to make the sides of an artistic material and the top of sopme metal sheet.
From what I remember, keeping wiring close to a ground plane helps miminize effects of EMI.
Like this:

[Tubeamp]

Wow....my congratulations Magnus ! Nice work !!!

[soundbrigade]

As it looks on the pic it is (was) an 6L6 oddwatt (Ming Da), now I have started to redo the driver/phasesplitter and sort of use the oddwatt-thing on the input/driver-tube.

I simple wanted to show a typical pic of a typical Kesselmarchian amp; wooden plint and metal top, in this case copper, but I have also alu, brass and alu/zink.
I have found good speaker connectors at www.vt4c.com that can pass through approx 25 mm and input connectors are mounted on some scrap metal och scrap PCB.

IF you want an all-plastic/wood/concret/textile ... chassis, use a metal lining.

[nyazzip]

in addition to the reasons already mentioned... starting in the 1800s, up until very recent times, the simplest, most practial and economic way to make a durable box or case for any purpose was to use sheet metal and bend it into shape.
now in this age of ABS plastics/composites, injection molders, and lightweight, cool-running components, sheet metal is not quite as mandatory as it traditionally was

[soundbrigade]

Ooops!

Wrong topic.

[Geek]

I've used a wood chassis. Tip: Use kiln dried wood for the chassis only that's relatively thick and not laminated - the thermal cycling will cause it to warp and split otherwise.

It's doable and safe, but there's a buch of precautions you have to take, including running a ground lead to ANYTHING metal that's exposed, including controls, tube sockets and iron.

Cheers!

[msmpe]

Thanks all! Good comments and food for thought.

I might try masonry board, and yes all the metal frames would be earthed. The signal leads would be sheilded. Heat is a concern as the tubes, etc are enclosed in a wood cabinet, but it has lotsa holes for natural convection. My structural "reinforcement" should preclude breakage (as long as UPS doesn't get a hold of it). The PST would not be on the masonry board chassis, and the OPT are small as this is a SE triode strapped at around 2W.

This came up because I was having difficulty getting my mits on some aluminum sheet. I've since found a good source at http://www.onlinemetals.com/ give 'em try.

[nyazzip]

This came up because I was having difficulty getting my mits on some aluminum sheet

the home improvement stores usually have a section for welding stock where they have various sheet metals, including diamond plate aluminum which is thick enough to support transformers...one side is "diamondized", but the other is flat

[Geek]

Got a truck or farm welding/repair/mod shop in your town? That's where I get my aluminum and it's about 50% less than Online Metals.

Mind you, aluminum is a commodity that has the RARE privilege of being far cheaper in .ca than the US.

[TerrySmith]

I've used online metals before, they can cut the aluminum sheet to any size you want for a very minimal or no cost!

[mesherm]

I made this chassis out of 1/4 inch Lexan. Used 1/2 inch thick for the base plate. Grounded all the trannies together. No hum. The fans were 120 volt in series so they ran very quietly. Just enough to force air out through the top plate.