Its only a 60W transformer for crying out loud.
Most AC line cords for old tube radios and modern PC's are only #18.
Many 1000W amps supply #16 as well as some with more power.
Carl
KM1H
----- Original Message -----
From: "Manfred Mornhinweg" <manfred@ludens.cl>
To: <amps@contesting.com>
Sent: Sunday, July 08, 2012 3:27 PM
Subject: Re: [Amps] Filament Xfmr
> Pete,
>
>> When I received the transformer all looked great to me except for the
>> secondary pigtail wires. The tube requires 6vac at 10amps, the pigtails
>> provided are about five inches long and are a #18 well insulated wire.
>
> For the primary that wire size is plenty, but for the secondary it's
> rather cheap.
>
>> Being concerned with the wire size it put the transformer under load and
>> drawing 10amps left it that way for about an hour. The wire did not
>> over
>> heat in that time but hey how about hours of operating.
>
> It won't change between one hour, and continuous use. The thermal mass
> of single thin wires in air is low enough that the temperature will
> stabilize after several minutes.
>
> The transformer proper will take longer to stabilize. One hour might not
> have driven it to its final temperature.
>
>> Should I be concerned with the wire size.
>
> If it survived the 1 hour test, and if the voltage delivered to the
> filament is enough, I would say you can use it without much worry.
>
> > I have looked for information on how to
>> figure how much current various wire sizes can carry and at various
>> voltages
>> and have not found anything.
>
> Wire tables are widely available on the web. Many of them list the
> current carrying capacity in different applications, per wire size, so
> you don't need to do the math yourself. But a quick and useful rule is
> this:
>
> In thick bundles, like in transformer windings, you can use up to about
> 3A per square millimeter. With very large transformers it's a little
> less, with very small ones you can go to 4A per mm^2.
>
> In bundles of a few wires, such as in house wiring, about twice as much
> current per area is fine and safe.
>
> For single wires in free air, it can be even a bit higher, as long as
> you don't get too much voltage drop.
>
> #18 is about 0.82mm^2. So it's fine for 2.3A in transformer windings,
> roughly 5A in bundles, and at least 7 or 8A for a single wire in free
> air. It won't melt or anything at 10A, but it might get noticeably warm.
>
> I would have used #14 for those pigtails, and #11 or 12 for the winding.
>
> Manfred
>
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> http://ludens.cl
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