heater wire

[iknowjohnny]

Do you think i'll be ok with 20 gauge teflon, or is it risky? I have some 16, but it's so hard to work with in this context and i only have it in one color making it a pain to keep checking continuity to know what end is what at each tube as i wire them up

[Structo]

Depends on how many tubes you have and how big the current demand is.
Typically most amps use 18 gauge.

But, on my D'Lite amp I ended up using 20 solid with no adverse effects.

[iknowjohnny]

it will basically be a 50 w marshall....2xEL34, 3x 12ax7. Possibly another ax7 in the future for verb, but not likely. Oh, and it's stranded if that matters. (but bends and holds almost as well as solid due to large tinned strands)

[Sonny ReVerb]

Some folks recommend bigger gauge wire for the power tube heaters and then drop down a bit for the PI and preamp tube heaters. The theory is that the power tubes draw the most heater current, plus all the current flows through that section. The PI and preamp tube heaters draw much less current. The power tube sockets generally have bigger lugs to work with which is a bonus.

If you're using EL34's, they draw almost 1.5 amps each for the heaters, so bigger is better. Each 12AX7, on the other hand, draws about 0.3 amps.

On my 18W build I used 18ga for the power tube heaters and then dropped down to 20ga for the rest. YMMV

[iknowjohnny]

Thats probably a good idea. I have some 16 and will use that for the PT's then drop to 20. Good idea, thanks.

[GibGa]

You can also double up the 20ga for the power tube first section, instead of using the large 16ga. I find solid 18ga difficult enough.

Also I've used white jacket wire and color coded that using large MagicMarkers when coding is helpful.

[azatplayer]

Each of the Z amps ive owned ran 20awg on all the heaters.

[Andy Le Blanc]

Most old gibsons and ampegs Ive been in used what looked to be telephone
wire.
The wire of the transformer carries the most current total, over sizing the gage
can leave you with a mess.

[v846]

A typical 50 watt Marshall draws about 4 amps and 20 ga is rated at 11 amps, more than sufficient for heater wiring.
heck 22 gauge is rated at 7 amps and I bet that is conservative.
btw It's the insulation that limits the wires amp rating.

http://www.powerstream.com/Wire_Size.htm

[Phil_S]

People are bandying about the rated number of amps for a given wire size. I want to raise a flag of caution here. The standard AWG chart for this is meant for "open air" wiring, not inside a guitar amp chassis, where wires are often "bundled". The heat associated with a closed space like a guitar amp chassis, and the bundling (i.e., twisted pair, or just zip tied together) are both important factors that derate the values on the standard chart. I don't know by how much, but these are things that do matter.

I believe the reason why some engineer decided on 18 AWG for heaters has something to do with bundling and small enclosed spaces. I suppose, 18 AWG to the power tubes and 20AWG to the low current preamp tubes is OK.

I wouldn't rely on 20 AWG wire being "rated" for 11A, though I do think it should be OK for most guitar amp applications and I have used it for the whole heater string.
Read here, the notes on Load Carrying Capacities.
http://www.powerstream.com/Wire_Size.htm

[iknowjohnny]

btw It's the insulation that limits the wires amp rating

I wondered about that actually, and it would seem to me that should definately be PART of it, but i doubt it's only that. I think it's common sense that would be part of it since a pathetically thin PVC coating could conceivably melt enough to cause a short if the wire gets hot enough. But i think the gauge is what would dictate whether it gets hot enough. But as far as the jacket goes, theres a good reason right there to use teflon ! I've never considered anything else for an amp because right or wrong it gives me peace of mind knowing it would take a nuclear weapon to melt the jacket. And in a context like a tube amp where it's heated up due to soldering and then abused by a hot amp for years, i just like knowing it can withstand the heat. Looks great too....nice vivid colors, shiny like candy !

[v846]

yeah I'm sure the PVC insulation melts before wire, doesn't copper have a high melting point?

[iknowjohnny]

Well, i think the issue isn't the wire melting....it would be the insulator OR the insulation in the transformer, IE varnish or whatever is used to isolate the windings. In other words, if the wire is too small the transformer windings would heat up and melt the insulation and cause the windings to short. So i think that along with the wire's jacket are the things likely to fail. And the wire being to small a gauge would be the cause. I just wanted to be sure 20 gauge wouldn't cause that.

[Zippy]

btw It's the insulation that limits the wires amp rating.

Not so. Current handling capability is a function of wire diameter.

Voltage rating is determined by insulation.

Eh, what do I know. I was a USN nuclear-qualified electrician and have degrees in applied physics and engineering. All that training could have been wrong...

[Zippy]

yeah I'm sure the PVC insulation melts before wire, doesn't copper have a high melting point?

Not for a metal. What do you call "high"?