RED-25 Assembly Guide
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You'll need the tools below to complete this build.
We recommend an adjustable-temperature station, such as the $40 Weller WLC100.
You can use 60/40 "leaded" solder or lead-free. We recommend 60/40 because it flows better and is easier for beginners to use.
You'll need a pair of good "snips" for cutting of the excess leads after soldering.
These tools aren't strictly necessary but can make your build a bit easier.
If you find the color bands on resistors a bit hard to read, you can use a meter to sort them with absolute confidence.
If you accidentally solder something in the wrong place, a desoldering pump can save the day.
Open up the parts bag and identify the parts. From left to right they are:
- 5x DOA Pins
- 2x Resistors
- 2x Input transistors (BC550C)
- 2x Power transistors (BD139, BD140)
- 1x Circuit board
Make sure especially to the BD139 and BD140 transistors. Although they are the same shape, they are two different parts that will go in different positions in step 1.7.
Place Pins in Sockets
Keeping the pins in place for soldering can be tricky, but luckily you've (probably) already got the perfect jig to hold them. Place the pins in the sockets of a piece of gear that accepts a DOA, such as the DOA Colour pictured. Make sure to insert the pins until they snap in. Also note that the RED-25 does not have a 6th ground pin.
Place the RED-25 circuit board over the pins and solder. Wait 30 seconds between soldering each pin so that the previous joint can dry. Once all the pins are soldered, remove the assembly from the sockets.
Bend the leads of the resistors and place them in the R11 and R12 positions. The resistors are not polarized and can be placed in any orientation. After you've placed them, bend their leads against the bottom of the circuit board.
Solder and Trim Resistors
Solder the resistors and trim the excess leads. Trim the leads down as close to the solder joint as possible without clipping the joints themselves.
Place and Solder Q1 and Q2
Place the smaller transistors in the Q1 and Q2 positions. Make sure to orient the transistors according to the outlines on the circuit board. As you did with the resistors, bend the leads against the bottom of the PCB, solder, and trim.
Place and Solder Q7 and Q8
Notice: Even if you skim the rest of the guide, pay attention to this step! Q7 and Q8 are two different transistors that must be placed in the correct positions: BD139 in Q7 and BD140 in Q8.
Place the BD139 transistor in Q7 and the BD140 transistor in Q8. Place them both with the text side facing the Q1 and Q2. Now double check:
- Is BD139 in Q7?
- Is BD140 in Q8?
- Are the sides with text facing Q1 and Q2 (away from the resistors)?
Once you're sure the transistors are in the correct positions and orientation, solder and trim the leads.
Before you wrap up, check the following things:
All good? Congrats on finishing your build! Have a question or problem? Drop us a line.
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