Hi Chaps,
Having just built 10 of these, I thought I would pass on some thoughts of how to approach them as I managed to get all of mine working first time (Yippee!!!!)
Firstly, use a method and stick to it: I use small margarine tubs for each step of Gary's assembly instructions and just put that step's components in it. Bring each tub over to the workspace for each step, use the components from it, double check before inserting them into the board. It sound laborious and takes longer, but it worked for me and avoids the need for any fault finding later. Then swop that tub for the next step's and repeat.
Use the thinnest solder you can find and a very fine soldering iron. Use a magnifying headset in conjunction with a good lamp over you work.
Insert the components for that step. Trim the component leads with a good sharp set of fine side cutters, and clean all the flux off the board with Isopropyl NOW. Check the work for that step there and then, correct any mistakes before moving on to the next step.
Always have an empty pcb to hand. This allows you to test if two pads are connected or not. For example, some of small caps are really close to the Millmax pins and the solder may look as if you have made a solder short. Use a meter to check on the blank pcb if the short should be there or not.
Build yourself a jig using Millmax sockets on strip board (Veroboard). This has two purposes: firstly it serves to help you line up the pins vertically before soldering in - see below on this, and secondly use it to implement a simple circuit such as a non-inverting amp of 6dB gain to test your finished work.
Use a signal generator as an input and a scope on the output if you can.
If you can, use a lab power supply that you can ramp up slowly. As you turn the voltage up, you will see less than 10mA being used up to about 9 volts. The output signal on the scope will be fuzzy and distorted up to this point. At about 9 volts the scope signal should start to become sharp and defined with the required gain. At about 14 volts, the current goes to about 20 mA and at 18 volts will just click into 30mA.
Any more current at the above voltages, or a distorted output at greater than 9 volts and you have a problem.
Always ramp the power down when you change the amps for testing.
When you have a good working amp, use this as your reference in case you suspect your test jig. This happened to me from inserting and pulling the amps and it turned out to be one of the strips on the strip board had a minute crack.
Regarding the Millmax pins, I put them in the socket on the jig, used a flux pen to smear flux over the the top of the pin and then just a tiny dab of solder to 'tin' the rim that connects to the underside pad on the pcb. I then put the pcb over the pin, applied solder from the top and pushed the pcb down. Do this one pin at a time. This then ensured that the underside pad was soldered to the Millmax pin and very cleanly. Clean the board with Isopropyl, check your work using the blank pcb for shorts if you need to and then move on to inserting the components.
I am very pleased with the results (thanks Gary) and am sure that sticking to a method is 90% of the job.
Cheers, Mike
