[TenTec] Working on PC board mounted RF power transistors

[Ken Brown]

> My Wellers are the models WP-40 and WP-25. My 'screwdriver tip' on the 
> WP-25 is probably 1/32 across the rounded tip.
>
I like Weller soldering irons too. There are so many kinds (of any 
brand) that it is important to pay attention to details. It is not just 
the power rating of the iron that matters, it is the temperature 
control. For desoldering RF power transistors from the printed circuit 
board you want the thermal mass and heater power rating of the larger 
irons. Say around 25 watts or more. You do not want that heating power 
uncontrolled though. Any iron with sufficient power rating for this job, 
without temperature control, can get to much higher temperatures than 
you want to subject your PCB to. If you use a lower power rated 
non-temperature controlled iron, to keep the temperature from getting 
too high, then it will not have enough heat capacity to do the job.

If you don't have the power, you'll have to mess with it longer and 
damage stuff. If you have the power and too high temperature you'll 
damage stuff quickly.

Weller (and others) make irons with magnetic thermal switches in the tip 
assembly, that switch the heater on and off to maintain a fairly 
constant temperature. That or some other temperature controlled iron is 
what you want. You do not want an iron that is just always on. Yes you 
could be successful with one of these, using a Variac or SCR control. I 
don't recommend it. Temperatur controlled irons cost less than many RF 
power transistors, and less than the trouble of replacing a damaged PCB. 
Plus they have applications for many other jobs.

DE N6KB