Aluminum tubing & B+ wiring

[tubenit]

Have any of you tried running B+ wiring on the outside of a chassis thru aluminum tubing that is grounded to the chassis?  OR seen an amp that uses that approach?  This would sorta be like using shielded wiring on a B+ wire BUT uses an aluminum tube to shield the wires.

I'm wondering IF running the B+ wires that go to preamp plates on the outside of a chassis would make any significant difference in floor noise? 

It would seem like the B+ wiring (to preamp plates) inside a chassis close to other components would add some floor noise.  So, IF one could have the wiring running across outside the chassis inside a grounded tube and then return inside the chassis at the point of  the turret that provides B+ to preamp plates, that this might reduce noise?

I don't have any current plans to use this approach, but have wondered about it for some time.

With respect, Tubenit

[shooter]

any significant difference in floor noise

aluminum isn't a very good faraday shield so I wouldn't expect much.

I did an "outside" on a SS amp but mostly an astatic thing, did the same thing with preamp filaments, but can't find pic
 

[jjasilli]

I'm not aware of anyone running B+ outside the chassis or even using shielded cable for B+, even in hi-end hi-fi amps.  This circumstantially indicates that it is not a worthwhile approach.

Also, aluminium tubing would not shield against magnetic interference, as shooter says. 

B+ is DC and well-filtered. It should not be a source of noise.  It could become infected by noise induced by some other source(s) -- e.g., AC filament supplies or incoming wall power; trannies or inductors which create magnetic fields.  It is more typical to shield those things, or use proper layouts.

[kagliostro]

I've seen small iron squared pipes used as shield for filament wires (inside the chassis) but not to shield B+


Something done similar to what you say, I've seen in double chassis amps (preamp on Top - Power Section on Bottom), a metallic flexible tube, similar to flexible hose for hand showers, look to Fender Excelsior, but there all wires that feed preamp section cross that pipe (B+ and Heaters)




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Merlin, in one of his books, as to reject B+ noise, say to add an (around) 200n capacitor to the filament pins of V1 (in parallel with heaters)

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Franco

[PRR]

The preamp B+ line has a big bypass cap, yes? I would not expect it to need shielding.

The OT primary (plate) leads are the strongest signal in the amplifier and like to leak INto everything. However they are also extra high voltage so dangerous to put in a pipe.