Shielded Heater Wires - Drastic Solution

[kagliostro]

Looking around I've find this drastic solution for shielded heaters

Kagliostro

[John]

  And you all called me crazy! Well thar's two us crazy 'uns out dere! 

[HotBluePlates]

Well, I guess one can do that.

There is, however, cable available with 18ga twisted pair, with an outer shield.

[kagliostro]

I agree that is an extreme solution

however iron is the better material for shields (excluding mumetal)

Kagliostro

[birt]

if you want to go that far it's much nicer to drill through the chassis and run the heaters on the outside.

[Fresh_Start]

Seems like I saw copper tubing at a hobby store not too long ago and was thinking it might make a decent shield for the first 1 or 2 stages of a preamp.  The problem I had was figuring out how to attach it permanently to the chassis.

In most amps, you don't really need 18 gauge heater wires except for the power tubes.  12AT7s or preamp pentodes draw a lot more current than 12AX7s though.  Where I'm headed is that shielded 22 gauge, twisted pair wire costs a LOT less than 18 gauge.

Cheers,

Chip

[mresistor]

attaching copper tubes. 

use some power cord clamps, and a ground wire. 

or maybe braze it or solder it directly to the chassis......

[proaudioguy]

I would think tightly twisting the heater wires together and moving them as far away from the circuit would be as good as any shield other than mu.  It's probably important that the twists are tight and the current is balanced. Seems the 60Hz radiation would cancel out within a short distance.  Has anyone done any tests to check the effect of the shields?  Even a 6dB reduction all else being equal might make it worth doing on a recording amp. Not much point in a combo amp I suspect.

[stratele52]

+1 proaudioguy

A "standard" heater wiring ,if well done, is as much quiet as any other method ; DC and shielded wire. I test both.