Bonehead newbie questions /Soldering wattage on pcb / Blue 3pdt switches

[BDC]

I'm building a couple of Tubescreamers with Tonepad PCBs and have a basic question or two.
I'm useing a 25w soldering iron. Am I pushing it a bit........Should I use a 15w.

I have read that the "blue" 3pdt switches manufactuer specify they require silver solder and that the plastic doesn't hold up to the heat.
This was info I gathered at the Fulltone site. I ended up ordering a couple of Fulltone 3pdt switches. Fulltone says they don't require special solder.

I've built an 18w amp completely but am new to pedal building........I'm no engineer as I gather many here are......

[calpolyengineer]

The blue switches definitely do not require silver solder, nor does anything short of maybe NASA (and EU). If blue switches were vulnerable to heat, silver solder would be worse because it needs more heat to melt. Also, soldering iron wattage is fine. I used a 25w for a long time and I thought it was on the lower side of usable.

-Joe

[smallbearelec]

I'm useing a 25w soldering iron. Am I pushing it a bit........Should I use a 15w.

25W will do fine.

I have read that the "blue" 3pdt switches manufactuer specify they require silver solder and that the plastic doesn't hold up to the heat.

The blue switch is made by the same factory that makes the Fulltone part. I have sold at least 100,000 pieces of the blue one, to both DIY and commercial users,  with few complaints. The Fulltone switch has a Bakelite body, and so is a little more tolerant of soldering heat. If you've already buiilt an amplifier, I strongly doubt that you will notice a difference.

Regards
Steve Daniels

[BDC]

Thanks, I actually use a 40 watter most of the time on amp work..Getting ready to build another...All parts I already have or are ordered!
Back to pedals
I must admit, Soldering on those little bitty pc boards is a lot harder than on turret boards....I think in the future I'm gonna try
perf board.....and spread things out a little more. Steve your my enclosure,led,diode & pot supplier for the tubescreamer project.

I bought 2 film caps (.22uf) in place of  tants for one of the tube screamers,is this gonna have an adverse affect?
For the other I had the tants.....Radio shack 2 blocks down the steet only had film.

[Mark Hammer]

The heat is, to my mind, partly responsible for novice builders saying the switch has "failed".

If you were to disassemble a 3PDT switch, you would see that inside are three separate teeter-totter/see-saw pieces that serve as rocker contacts.  They pivot on the inside part of the centre solder lug that protrudes through the plastic portion of the switch.  Press the switch and an internal mechanism makes one side go up and the other go down.  Press again, and they change which is up and which down.

During assembly, a small dab of nonconductive grease is placed near the pivot point.  This has two roles.  One is that it holds the rocker contact in place so that it doesn't fall out or get unseated prior to the upper and lower halves of the switch being put together.  The other function is that it provides some damping so that this free-floating rocker contact does not jiggle when in use and produce tiny momentary discontinuities in contact.  What you might call mechanical debouncing.

When heat is applied for too long, it can become conducted along the rocker contact and result in that dab of grease melting and flowing all over the surface of the contact.  As noted above, it is nonconductive.  This means that when you press the switch and that side of the rocker contact gets moved closer to the inside part of the solder lug for the purpose of making a connection, there is this goop on the contact preventing electrical conduction.  I have personally taken several switches apart and "rehabilitated" them by cleaning the melted grease off, reseating the rocker contacts, and closing the switch up again. This is how I learned about the phenomenon.  What I am describing also explains very nicely how it can be that one set of contacts on a switch can fail while others mysteriously don't; the overheating is specific to the rocker contact and associated set of lugs you are soldering at that moment..

So, what can you do to prevent it?  The general strategy is to get in and out quickly so that heat build-up does not occur.  The second half of that is to reduce whatever heat build-up is unavoidable so that it does not result in grease re-flow.

1)  Use a higher wattage soldering iron.  25W is good, but I imagine 35W is better.

2)  Dab a bit of flux on the solder lugs so that solder flows efficiently and quickly.

3)  Pre-tin any connecting wires or components so that they "want" to form a joint fast.  Pre-tin the solder lugs on the switch too.

4) After you've tinned the solder lugs, wait for a bit or apply some form of heat-sink to them to cool them off.  A small bit of paper towel with some water can work just fine.

5) Keep your meter handy and, using the continuity-beeper function, identify which set of lugs is NOT currently in contact with the rocker contacts inside (i.e., open circuit between that lug and the centre lug).  If it is not in electrical contact, it is not in thermal contact, so you can now solder any wires or components to it.  Let it cool off, and then press the switch to change which side is in thermal/electrical contact and do the other side.  Wait a bit for things to cool down and then do the centre lugs.

6)  Note that since the dab of grease is applied in the middle on the inside and the centre lug is always in thermal/electrical contact with the rocker contact on the inside, you need to be especially careful not to overheat the centre lugs.  You can be a bit sloppy with the outside ones, but be MORE careful with the centre lug.

Fast efficient soldering, and effective hat management will allow every switch to function well for you the first time you fire it up.