My Personal Project - Amplifier: October 2012

The last week of work has been by far the most productive week in terms of understanding, accomplishment, and overall completion.

The first thing that I had to finish was the fibreboard. At the start of the week, I had most of the capacitors and resistors on it. This was tricky because I had to look at the circuit diagram and then back at the schematic to make sure that I got everything right. The fibreboard traces and wires on the underside of the board were the hardest to do because there were so many holes. It was rather easy to get confused and put a wire in the wrong hole.

Rafael came over on saturday to make sure that I hadn't done anything potentially damaging or even life threatening. There were 3 main questions that I had for him.

1. How do you know where to put all the cables that come off of the power transformer when some don't show up on the circuit diagram and the schematic.

2. How and where do I connect the ground bus wire?

3. How to get to the 6.3 heaters from the power transformer and the pilot light?

The first question has yet to be answered and I'm going to meet up with him next saturday to clear it up and finish it.

The second question, however, has been solved. The bus needs to be attached in some way shape or form to the ground wire that comes off of the mains outlet and the chassis. The easiest way to do this was to attach both onto a screw and bolt that were conveniently near where the AC mains line comes into the chassis. This prevents the chassis from ever becoming live.

Rafael also pointed out that I had a capacitor between the ground and the live wires which is arbitrary and not suitable for British electrical law.

The third question I figured out by myself on wikipedia. Each of the tubes needs to have 2 twisted 6.3 heater wire so that they can warm up before being played. The way to do this involved a fun and slightly unorthodox method. Basically, I had to strap two wires in place on the side of a desk and then attach them both to a power drill. By spinning the drill head, the two wires spun around each other tightly so that there would be no hum when the amp is played. I connected these to one of the tubes yesterday, but I'm going to do the rest today.

Finally, I sent an email to my supervisor telling him about the state of the project and my progress so far. I still need to finish up some small components, attack all of the 6.3 volt heater wires, install the fibreboard into the chassis, finish off the wires in the power transformer, and connect the AC mains line.

I suspect this should be done and tested by Saturday!