heater wire

[guitardude57]

Electrons travel along the surface of the wire, not in it..........doesn't matter if solid or stranded.

Stranded definitely can handle more traffic. So in order to not have huge wire gauge, use stranded. I have used both in wiring heaters, but IMO stranded wire is somewhat better for high current draw like EL 34's.

And like Zippy said, voltage rating is the for the insulation.

[Merlinb]

Electrons travel along the surface of the wire,

Not at 50/60Hz it doesn't!

[M Fowler]

Solid core wire of the correct gauge is appropriate for heater wiring.

[iknowjohnny]

Hey merlin, what are your thoughts on twists per inch? Someone mentioned a certain amount which is not nearly as tight as i usually do it. Does it really matter? I would think not since the few amps i've built have been very quiet

[M Fowler]

Take a look at a TW lazy loop wiring or Dr Z no twist wiring how come no noise.

twists per inch?

[Sonny ReVerb]

Electrons travel along the surface of the wire,

Not at 50/60Hz it doesn't!

From Wikipedia:

Skin effect is the tendency of an alternating electric current (AC) to distribute itself within a conductor so that the current density near the surface of the conductor is greater than that at its core. That is, the electric current tends to flow at the "skin" of the conductor, at an average depth called the skin depth. The skin effect causes the effective resistance of the conductor to increase with the frequency of the current because much of the conductor does little. Skin effect is due to eddy currents set up by the AC current. At 60 Hz in copper, skin depth is about 8.5 mm. At high frequencies skin depth is much smaller.

Since solid 18ga wire is about 1mm in diameter, I guess skin effect is negligible. Interesting!

[Bierschinken]

Hello,

sorry, but the skin-effect really only matters at frequencies well beyond our hearing range.

You can easily calculate how much current your wire is able to handle via the following formula;
Ri= l/(x*q)

Ri is the wire´s resistance
l is the wire´s length
x is the materials conductance (58 for pure copper)
q is it´s diameter in sqmm

With that resistance, you can calculate the power dissipation with your heater current.

You´ll see that a 1sqmm thick wire can handle huge currents!
As wall installations here in germany they use 1,5sqmm diameter for currents of up to 13A.
So there is no need to worry about the diameter in standardamps with maximum heater currents of 6A - 7A.


Swen

[Merlinb]

Hey merlin, what are your thoughts on twists per inch? Someone mentioned a certain amount which is not nearly as tight as i usually do it. Does it really matter? I would think not since the few amps i've built have been very quiet

I haven't really looked into it. I have always imagined that the magnetic field suppression increases with twists-per-inch to some kind of asymptote, but I could be wrong. I twist fairly tightly (about 4-5 twists per inch), simply because it's neat and doesn't unravel so easily
(I never use solid core for heaters, it always snaps when I twist it, although I know some people seem to use wire that would be better suited to anchoring a ship than feeding little heaters, but probably doesn't snap so easily!)

[iknowjohnny]

Thanks Merlin. Thats what i wanted to hear because i want to use a very tight twist for neatness/looks.

[M Fowler]

I twist both solid and stranded heater wire, just don't get carried away with the drill when you twist.

Or you can do the twist by hand, I've done that too.

I like to run the heater string overhead as well keep it off the deck of the amp chassis.

[bigbeck]

[quote="iknowjohnny"]Do you think i'll be ok with 20 gauge teflon, or is it risky?/quote]

Actually 20 gauge is large enough for a quad of KT88's. Remember,the first power tube's current draw should not be figured in because the PT heater wires carry that load. For an Express,if you hook the PT heater wires up to the first EL34, the highest current that flows through that 20 gauge wire is 2.4 amps. So even 22 gauge is quite safe.

Also,you do not need to twist heater wires. Many people use zip cord(speaker wire) - it will cancel hum just as well as twisting. It may even work better. I have wired the heaters with that clear 22 gauge speaker wire on my last 6 builds with no problems. I can't tell which method is better for reducing hum - they seem about the same to me. It's just easier using speaker wire (zip cord).