Solid core wire - ok for heaters?

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shipwreck
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Solid core wire - ok for heaters?

Post by shipwreck »

As I understand, the heater supply is low voltage but high current. And wires are usually twisted to reduce hum. Is stranded wire a better choice than solid core for this application? With less than perfect soldering technique, the solid core could get hot enough to melt the insulation.
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Re: Solid core wire - ok for heaters?

Post by pompeiisneaks »

This, I think, is one of those religious discussions. Basically I've heard people scream with the most passioned approach that (insert wire type here) is the BEST ALWAYS! The most important part to make sure you do, is use the right gauge of wire for the application. I use 22 Ga wire (solid core) for my preamp stages and then for the power tubes I use 18Ga. (for all connections, power, heater, ground, etc.)

I've recently been reading and even seeing in a few amps, that twisting of heater wires isn't even needed so long as you keep them away from the signal wires, I'll still always twist mine, it doesn't take much effort and I also like the look. I've had great luck with pretty damn quiet amps, with a few exceptions that turned out to be grounding issues that I resolved :)
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10thTx
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Re: Solid core wire - ok for heaters?

Post by 10thTx »

Correct wire gauge is important. I've used both solid core and stranded for heaters. I can't tell any difference in noise or performance.

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Re: Solid core wire - ok for heaters?

Post by telentubes »

I've never used anything but solid core 18AWG
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mhartman
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Re: Solid core wire - ok for heaters?

Post by mhartman »

Fender used solid core for heaters back in the day. I've had many problems with amps, but solid core on the heaters was never one of them
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M Fowler
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Re: Solid core wire - ok for heaters?

Post by M Fowler »

I'm all over the place with wire type and whether their solid or stranded on the heaters.

I've used both 18 solid, 20 solid, and 20 stranded on the heaters with no problems.

Just recently I had my first broken solid core heater string that I had to track down and it was on V1.

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rooster
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Re: Solid core wire - ok for heaters?

Post by rooster »

It's been reported that Fender used #18 wire (solid core) on their heaters from various sources when in fact they used #20 on the BF series. I use #20 solid core and never had a problem.
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Doxie man
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Re: Solid core wire - ok for heaters?

Post by Doxie man »

20AWG is plenty good for everything in your amp chassis. That's all I have ever used and NEVER once had a problem. Max current rating for chassis wiring (according to the American Wire Guage table) is 11A. You'll never get close to that in a guitar amp build. 18Awg is waaaaay overkill and simply not needed and is more difficult to work with when wiring up the novels. Wire twisting is another unnecessary task. Just run them parallel , keep them away from signal wires and all is well. Many famous amp circuits do not twist their filaments and there is no problem with noise. Soldano, Hiwatt comes to mind.
Last edited by Doxie man on Sun May 28, 2017 10:16 pm, edited 1 time in total.
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Re: Solid core wire - ok for heaters?

Post by Doxie man »

My latest build has no twisted filaments and it's stone quiet 👍
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mhartman
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Re: Solid core wire - ok for heaters?

Post by mhartman »

Doxie man wrote: Sun May 28, 2017 10:09 pm My latest build has no twisted filaments and it's stone quiet 👍
Nice looking build!!
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RJ Guitars
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Re: Solid core wire - ok for heaters?

Post by RJ Guitars »

Here is a decent web site for info on this... http://www.engineeringtoolbox.com/wire- ... d_419.html

Looks like if you don't include a "mojo element", you could wire most amps with #24 solid core (all the same color if you prefer) and you would never exceed any current ratings.

You'll have to avoid the really big dogs with this strategy since something like an EL34 will gobble up lots of heater current and you'll need more juice for a few of them.

In my builds I sorta like #20 teflon insulation around a nickel coated copper conductor. I also tend to like the irradiated PVC that has a higher insulation melting point. I totally dislike working with the official trainwreck wire with the low temp PVC although the wire itself is good stuff there are just better options available these days.

Also - do everything Doxie Man said and add in one more thing - when you do cross a signal wire over power (or other) wires, attempt to do it at 90 degrees.
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Ken Moon
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Re: Solid core wire - ok for heaters?

Post by Ken Moon »

The benefit of using solid core wire is that bends in the wire stay in position without having to use a bunch of cable ties or other methods that are used to keep stranded wires where you want them.

The drawback is that solid core wire breaks easily, compared to a wire of the same gauge made of anywhere from 7 to 19 strands.

I've done some experimenting with this, and found that any solid core wire I tried developed cracks or broke entirely after making as few as two 90-degree bends in the same spot (I bent the wires over to a 90-degree angle, then bent them back straight), and none made it past 4 bends without damage.

So, when using solid core, if you make a bend in the wrong place, just cut off the bent part and re-use the shorter wire somewhere else, or just throw it away.

If you do this, solid core will be as reliable as stranded in a guitar amp.

The only remaining difference is that the stranded wire will hold up better under extreme vibration without breaking, but hopefully your guitar amp won't have that sort of a problem, unless it's a combo set on top of a 4x12 cab :evil: A head usually has rubber feet, which help dampen vibrations. That's one reason I like heads with large rubber feet.

I personally love teflon-jacketed silver-plated copper stranded 20 gauge for all my amp wiring, except for around the AC input/power switch/power tranny/choke/resevoir cap, and the power tube heaters, where I use 18 gauge.

22 gauge is really fine for everywhere I use the 20 gauge, but it's just so small :shock: Kinda like those teeny little 1n4007 diodes or 1/8 watt resistors - I can lose a couple of those under my fingernails and not even notice :roll:
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romberg
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Re: Solid core wire - ok for heaters?

Post by romberg »

RJ Guitars wrote: Tue May 30, 2017 2:49 pm Here is a decent web site for info on this... http://www.engineeringtoolbox.com/wire- ... d_419.html

Looks like if you don't include a "mojo element", you could wire most amps with #24 solid core (all the same color if you prefer) and you would never exceed any current ratings.

You'll have to avoid the really big dogs with this strategy since something like an EL34 will gobble up lots of heater current and you'll need more juice for a few of them.
I use this line of reasoning too. A little simple math and that table lets one know if the wire gauge and type will handle the current. And one can estimate the current using the tube data sheets. For example a typical 50watt amp may have two el34 power tubes and three 12ax7s. The el34s draw 1.5A and the 12ax7s draw 0.15A of filament current each.

Since the filaments are wired in parallel, the first run (from PT to first power tube) carries all the current (1.5 * 2 + 0.15 * 3 = 3.45A). Then the next run carries 1.5A less (first tube current subtracted). So, 1.95A. And the current continues to drop on down the line.

At first glance at the above table shows 22 gauge solid core having a max current of 5A and seven core of 2.1A. So, if you wired the entire string with 22 gauge the stranded would exceed it's max rating but the single core would be fine. But would single core really be fine?

At the bottom of the table they show that these values are corrected for temperature. I bet the inside of an amp chassis can easily get over 105F (41C). In which case solid core 22 gauge is only good for 3.55A (5A * 0.71) and the seven core is down to 1.4A. This makes the use of 22 gauge solid core look sketchy for the entire run. But would be fine for everything after the big power tubes (were the current is down to .45A). Which is what RJ points out.
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xtian
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Re: Solid core wire - ok for heaters?

Post by xtian »

romberg wrote: Mon Jul 24, 2017 9:35 pm Since the filaments are wired in parallel, the first run (from PT to first power tube) carries all the current
Wait, what? In parallel heater wiring, all wires carry the same current. Right?

In SERIES wiring, the first run must carry the full current for the entire set of heaters.


EDIT: I'm an idiot. I stand corrected.
Last edited by xtian on Tue Jul 25, 2017 6:46 pm, edited 1 time in total.
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romberg
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Re: Solid core wire - ok for heaters?

Post by romberg »

xtian wrote: Tue Jul 25, 2017 1:42 am
romberg wrote: Mon Jul 24, 2017 9:35 pm Since the filaments are wired in parallel, the first run (from PT to first power tube) carries all the current
Wait, what? In parallel heater wiring, all wires carry the same current. Right?
If all of the filaments are in parallel then they will all have 6.3V on them. But the current will not be the same on every run of wire. The wires closest to the transformer will carry the sum of all currents down stream. For example if you just were powering one 12ax7 then the current would be:

Transformer <--- 150mA ---> 12ax7

But two 12ax7s in parallel would look like:

Transformer <--- 300mA ---> 12ax7 <--- 150mA ---> 12ax7
In SERIES wiring, the first run must carry the full current for the entire set of heaters.
I believe if all filaments are in series then the full current is carried by every segment of the run since it forms a single loop. The current can drop in parallel because each segment of a parallel configuration makes its own loop.

So for parallel:

Code: Select all


Transformer ------- 300mA  -------+-------150mA-------------+
                                  |                         |
                               12ax7                     12ax7
                                  |                         |
Transformer---------300mA --------+-------150mA-------------+

But series:

Code: Select all


Transformer --------300mA----------- 12ax7 ------300mA--------12ax7------+
                                                                         |
Transformer----------------------300mA-----------------------------------+

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