Ossus Amplifiers - Step 10, wiring and installation.

Before I get started I have to admit that this entry is long overdue. The truth is that the amp has been finished and in fine working condition for three weeks now. I've been a bit pre-occupied playing it and doing some other fun stuff that I'll chronicle in future posts.
So, where were we when I last left off? Oh, everything was done save the electrical hookup and final install. The turret board was drilled and the turrets installed. The chassis was drilled out to fit the tubes, transformers, the pots (potentiometers for volume, bass, treble, drive), the switches, and the power cord. Next up, wires and solder.

I cleared off a desk in my place and set things up to do the work. I have a nice soldering iron, lamp, some mats, a good chair, and a nice stand that can hold things while I work.

Before I got started I had to peek at the face and rear plates that I had etched. Up until now I had not really seen the results. I was waiting to do the drilling first. Well, I'm very happy with the etching.

Nice eh? Seeing the face plate sitting there really pushed me to start the work on the electronics. I wanted to start slow, pick some easy things, things that I could feel good about and work up from there. So, I started by mounting the tubes and transformers.

If you took the time to drill out the chassis properly and accurately then the pieces should just slip into place. Me? Well, I had to use a grinder bit and some persuasive force to clean up the holes to a point where things fit properly. I wasn't too far off, but far enough to require some minor adjustments.

A view into the interior of the chassis shows how the wires from the transformers get inside via holes with grommets to prevent chafe. A photocopy of the turret board layout to scale fits properly in place inside the chassis so I placed the turret board in just to get a view of how things were going to work out.

Next I put on the face and rear plates. I did this using some automotive epoxy which was totally overkill. The cement dried rock hard (really, as hard as a stone) and did the trick. A good epoxy would have done just as well. At least I know that my plates are never coming off. Ever. With the plates on I could install the pots and switches. This was easy, but I did learn an important lesson. You can over tighten a nut and strip these little gizmos. Don't do that. Also, some pots had alignment flanges. If I'd know that ahead of time I might have set the chassis up to accept them, but its really just overkill for this project. Finally, the two 1/4" jacks were installed. A self grounding one in the front, a normal one in the rear. I should have looked for fancy flush mount plugs, but these look okay.
At this point I stopped for the day. I had done a good bit, next up was the turret board and I wanted to be well rested and alert before I started that work.

First off I laid out all the tools and parts I'd purchased for the electronics. I inventoried them against some printouts I had and felt good about having everything I needed to put things together. Well, to be honest I was missing a capacitor and a resistor, both on back order, but that wasn't such a big deal.

I used my fancy resistor lead bending tool and put in the first resistor. Right off the bat I knew that I'd never use that bender tool again. Its overkill and I'm the sucker that bought it. A good pair of pliers and some careful bending and you are done. So I placed in the first resistor and I marked the fact on two printouts I had and on the resistor packaging. In doing so I kept perfect track of what I'd used and where it had gone. This turned out to be a life saver later on in the project. First I'd highlight the inventory sheet. Next I'd highlight the part on the layout. Finally I'd write on the label on the part's packaging where I'd installed the part (resistors are names 'R' and a number like 'R1', so mark the package 'R1', capacitors are 'C' and a number and so on).

And so it went, part after part, left to right along the board. At this point there was no soldering at all. Just part placement. You'd think that the parts would fall off, but no they don't. As you place a part on the turrets you carefully bend the wires around the turret posts and so they become fixed to the board. Take the time to try to keep the amount of wire uniform on either side of items, that reduces noise. Also, try for symmetry as you place parts, again that reduces noise. Finally, try to layout items in such a way that you can see what the part is. Later in life someone will have to fix this amp and figure out what the heck you did and why. Make that easy now.

Again, I stopped for the day at this point. Note the highlighted layout picture to the right of the chassis. Without that I would have missed something. I placed the board into the chassis, still unsoldered, just to get a look not to mount it.

Now it was time to solder the parts to the turrets. I placed the turret board into my clamp and set things up. Gravity will help the solder flow into the wires at this angle. Use proper solder, not the cheap stuff. Also, have at least two head sinks and a few clamps. Use them on every joint to protect the capacitors and other parts from damaging heat. As you solder highlight the joints on the same diagram you were using earlier. Doing this will help you keep track of things.
Again I stopped for the day when I finished this stage. Its tedious and complex and there was no reason to rush.

The next big stage is to place the board into the chassis and then wire the components together and to the proper locations on the turret. Take your time on this, plan out the wires. Work in a pattern. I worked clockwise starting from the power switch and heater wire on around. Some of the tube hook ups and complex pot wiring I left for last so that I would have time to hone my soldering skills. Again, as you wire things up highlight each wire. Do one wire, highlight it on the picture, then plan out and do another wire. I used solid core 20 gage wire for the hookups. I used 20 gage stranded wire with teflon insulation for the heater wire (the black and green twisted wires) as someone told me that was the best combination for the least amount of noise. There are two resistors on the turret board that are optional if you choose to ensure that you keep your heater wire lengths consistent with either an even or odd number of turns. I wasn't going to pay that close attention to that, so I kept those resistors in the mix.

It took some work to get the chassis to fit into the cabinet. Turns out that I'd made the tolerances a bit tight, almost too tight. There was a point where I considered building the cabinet over. Turns out some of the wood pieces shouldn't be glued in before the chassis is installed. Who knew? No one told me that. I made it work with only a few small sacrifices.
Amplifiers have a large amount of electricity flowing through them that can kill you if you do the wrong things. When I first started the amp up I used the trick of a modified plug with an inline lamp in one socket and the amp in the other. If the amp had a short the lamp would glow brightly. When I turned mine on the lamp didn't even flicker a bit. I was almost concerned that my test contraption was broken. I did a lot of testing for stray voltage. I waited a while for smoke or excess heat to show up, but there was none to be had. With that, I plugged in my guitar and let it rip. And it worked. Well mostly. It turned out that I had a short in one of the more complicated shielded wires from the drive pot to the turret board, but when that was fixed the amp sounded sweet and was much louder than anticipated. Much more than you'd expect from a 5-7 watt amp.

Here is the amp, lit up and running properly. Adjusting the drive can take the sound from Muddy Waters to the Scorpions. The amp has range and reacts in a very sensitive way to the particular guitar and the volume sent to it from the guitar. Basically, I couldn't be happier. I have a functional guitar amplifier that I'll keep forever. As a side note, my guitar teacher thought so much of the amp that I'm now helping him to build his own exactly like mine.

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