> I did a search thru Weller's website earlier today for some specs, but
> came up with nada.  Just checked how stuff works, but nada again.  Oh
> well.

Just to get things straight:

Weller/Cooper WTCP use a magnetic switch that uses the Curie temperature
of the tip (!) to sense temperature and cut the heater when it is reached.
It's an on/off system that will cycle all the time. Extremely reliable and
well proven. Other Weller irons use electronic thermostats and a different
tip heat sensor (rtd).

Metcal (at least the ones we saw) use the Curie temperature of a
distributed ferrite like material in the tip. When that is reached the
ferrite stops absorbing RF. It does this by volume so the heat is very
uniform and prompt in coming on and off. The black box contains a RF power
generator and the cable to the iron is coax. If you work with RF (specan
etc) and must have the iron going while you work then this may be a
problem. Otherwise very good and very expensive.

Most other thermostated irons use a special tip heater which has a built
in heat senser (RTD usually). The control box contains a thermostat with a
knob that sets the temperature. Such are Hakko, most Goot, Weller etc.

Most unthermostated irons (a la what you call rat shack ? - why ? did you
ever see an electronics store in another part of the world to compare with
?) use a simple heater wired directly to 24Vac or 110/220Vac. The tip
reaches its working temperature when its heat loss to the environment
balances the power input. Their temperature changes with the time of day,
your breath etc.

The only thing that the tip must do besides getting hot enough to solder,
is to be wetted by solder. All noble metals reject solder (silver does not
- beware). So they cannot be used for tips. Zinc plated steel is most
often used for cheap tips. The gray plating on the tip Olin L. mentioned
seems to be Zinc. That would turn gray after a while.

The things I look out for in an iron for general use:
- Can be ground separated and has insulation to match (soldering a wire to
the + pole of a lead acid battery with a grounded iron and grounded
battery - can be a memorable experience)
- Has reshapeable/hard cleanable tip (i.e. not iron plated copper - iron
plated copper is good for heavy duty precise work but not necessary for
general soldering imho)
- Has removable/replaceable tip - if it's expensive enough (the iron) and
the tips are not single-sourced (price !!)
- Has some sort of temperature stabilisation so it won't ever run too hot
(gas powered irons fail here - also with memorable results sometimes)
- Has screw-on cap or other tip protection if it is to be used outside the
lab

Peter

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