Circuit Board Wiring

I now have all the parts. Lots of resistors and capacitors (see photo above). It is kind of amazing that all these little bits are going to become an amplifier.

Test-fitting all components has proven to be a good practice. The same applies with the electronic components to be soldered to the turret board. I bent the leads and test-fit each part before soldering. This helped me to possibly minimize future problems. 

One thing I was aware of when placing the components was the turret board mounting screws. I had to make sure these screwheads weren't obstructed by wiring or capacitors so that I can re-mount the board upon completion. That is why you see the strange bend in some of the capacitor and resistor leads (see red arrow in photo below).

Soldering the turret board went very smoothly. I quickly got the hang of it, and my solder joints kept improving each time. I like the way the turrets work as opposed to standard rivets: solder the component to the top of the turret, and solder the lead wire on the bottom of the turret (or backside of the board). I simply did some estimation as to how long each lead wire should be, hoping to err on the long side. I tried to assemble as much as possible before re-mounting the turret board to the chassis. 

By soldering most of the stuff OUTSIDE of the chassis, I have more room to move around and in turn can make better solder joints. Also, notice the notch I cut out of the turret board in order to make clearance for the 1/4" jacks of the footswitch and speaker (see photo below).

The original Vibro Champ has four (4) grounding points coming off the circuit board. Each is soldered directly to the steel chassis with a huge ugly glob of solder. I can't replicate this for a few reasons: 1) I can't solder to an aluminum chassis properly, and 2) I'm trying to keep things inside the chassis as neat and orderly as possible. Therefore, I opted to connect a short wire from each point to a common grounding lug and screw, mounted directly to the chassis (see photos below). When tested with a multimeter, each connection made a positive ground, and hopefully it will hold up just as well.

Unless I run out of cloth-covered wire (looks like I should have ordered 6 feet of each color), I should be able to get the rest of the chassis wired up in one or two more sessions.

Trial and Error

All the parts are here except the bulk of the resistors and capacitors. By the time they arrive, I should be ready for them.

Today I drilled all the remaining holes in the chassis except the ones in the sides that will be used to secure the chassis to the wooden cabinet. I can wait until the cabinet is completely designed before I drill those.

I also test-mounted everything I have so far: the transformers, fuse assembly, AC power cord, tube sockets, Cap Can, pilot light assembly, on/off switch, potentiometers and knobs, input jacks, footswitch jack, and speaker jack. Everything fits nicely (well, almost. . . but more on that later).

It's really starting to look like an amplifier, now.

Slight Screw Up

The thing about trial and error is that eventually, you will make an error. It's inherent, and I'm surprised it took me this long to make a goof like I did. I was so concerned about making sure the knobs and everything on the top control panel lined up properly, I drilled the holes for the speaker and footswitch jacks slightly higher than they should have been (see above photo).

I put them where they are for a reason, since I was attempting to leave enough clearance for the heater wires that heat the tubes. However, as it turns out, the heater wires will probably go on the opposite side of the jacks anyway, and now, once you insert a 1/4" plug, the very tip of the plug just barely touches the turret board (see photos below).

In order to fix my blunder, I have come up with three options so far: 1) raise the turret board with longer standoffs or spacers, 2) relocate the jack holes, or 3) cut a tiny notch out of the turret board at the spot where the plugs might rub. Option #3 seems most logical, easiest, and makes the most sense. Luckily, I'm pretty sure the spots needing to be notched aren't at a major juncture on the circuit board, meaning a small V-shaped cut shouldn't cause further problems. 

Next on the agenda is to begin wiring, starting with the AC input and heater wires. Hopefully, unless I do indeed shock myself, the next post will have photos with some glowing tubes!

Taking Shape

The transformers and a few other parts from Weber came in today. I had to go to the Weber website to get the schematics for the transformers, as they weren't included in the shipment. There are a few changes in wire colors from the original Vibro Champ's trannys, but by comparing the schematics for both, I figured out which wires are which. There will be a few extra wires on the power transformer that will need to be clipped and taped off. These extra ones are for alternate input and output voltage configurations.

Also from Weber, I received the multisection electrolytic capacitor, or Cap Can. I am very impressed by the build quality of the components from Weber.

In order to transfer my drawings to the metal, I cut a strip of graph paper at actual size, drew the hole locations on it, and then used that to mark on the chassis. I was sure to make the drawing on the strip a mirrored image, since the original hand-drawn plans were a view from inside the chassis and I was cutting from the outside. This method seemed to work pretty well, and it was easy to get the chassis to look like my sketches.

Before cutting I placed the components on the chassis just to get an idea of what it will look like once complete. By doing this, I was making sure the tubes weren't going to be too close to one another or the Cap Can. After some last-minute tweaking and slight repositioning of a few holes, I was ready to cut.

I decided not to use a UniBit to drill the large holes for the tube sockets and Cap Can. Morgan Jones' book recommended not using a bit on a hole larger than 1/2 inch, stating that anyone trying to do so "is just asking for trouble." Rather, I used a unique tool called a Nibbler. It takes quite a while to chip away at the sheet metal, but it is very controlled and leaves a clean edge. I used a 11/32" bit to make the starter hole, then there is enough room to get the Nibbler in and cut out the appropriate hole. Of course, I filed down the edges to smooth them out as best as I could afterward.

After getting all the holes cut, I tackled the holes for the power transformer. The larger rectangular hole took quite a while to cut, and I recommend using padded gloves if you are using the Nibbler for a prolonged period of time. I used fingerless mountain biking gloves, which kept my fingertips free for fine detail work. 

You might notice in the photos that the output transformer is slightly elevated off the chassis. I lifted it with a few washers for two reasons: 1) to allow the output wires to pass underneath for a tidy look, and 2) to allow clearance for the heads of the turret board standoff screws. I used a rubber grommet as insulation/protection in the hole drilled for the output transformer leads.

I attached all the pieces I had drilled holes for thus far for a nice test fitting, and everything looks really nice. At last, this thing is beginning to look like an amplifier!

After mounting the big, heavy power transformer directly on the aluminum chassis, it became apparent that I should go ahead and use a piece of aluminum angle trim to brace from the inside of the chassis. While the project box is holding up the transformer now, it might not after several gigs and roadie abuse. There really is no reason not to make it as robust as possible, since it's easier to do that now rather than trying to go back and brace it later once the whole thing is completely wired.

Turret Board Installation

I have a pretty good grasp of where all the components will be mounted in the chassis. Now the time has come to begin drilling. 

In order to prevent cutting my hands and wrists on the sharp metal edge of the chassis, I placed a folded piece of gaffer's tape over it. Masking tape probably would work just as well, I just wanted to make sure to use something that would release easily when the protection was no longer needed.

 

The first step was to drill the mounting holes in the turret board itself. It came pre-drilled for all the wire passage holes, but I needed to create the holes that I will use to mount the board to the chassis. The material the board is made from is surprisingly tough, and drilling through it took more force than expected.

Once all four mounting holes were drilled in the turret board, I used a ultra-fine point permanent marker to mark the location of each hole onto the chassis.

Next I used a small nail and hammer to mark the location through to the other side of the chassis. I could have drilled through this side, but when drilling through almost any material, you get some messy edges on the back side, and filing them off leaves some roughed-up areas. In order to keep that rough filed area hidden, I drilled from the outside of the chassis and filed the burrs from the inside, keeping it completely hidden.

I used the marker again to mark the location of each hole, this time from the outside of the chassis.

After drilling and filing those four holes, I mounted the board on standoffs for a test-fit. Everything lined up nicely, and the standoffs are going to keep the turret board secure and elevated to prevent unwanted shorts.

Finally, some physical work has been completed on the amp! Everything up to this point had only been planning.

Layouts

The got the turret board today. It seems very nice. I know I probably could have saved some money by making one from some phenolic board and rivets, but since this is my first time I am trying to reduce the possibility of error on simple things. The board from Triode is very well built and seemingly indestructible. 

I got a piece of aluminum sheet metal from Tractor Supply Co. (much cheaper than Lowes) to practice metalworking. I learned long ago to practice on scraps instead of ruining your expensive materials.

Using the computer to do mock-ups of chassis layouts has been really helpful. I used Adobe Illustrator to arrange and re-arrange components all over the place. It really helps to visualize what things might look like once put together. However, when I got to a point where I felt like I was pretty close, I dragged out the drafting gear. While the computer is a great kick-start, there is no substitute for using graph paper, a compass, and straight edge. That tactile connection of using a pencil and paper is something a computer cannot replace. So, I drew up some elevations and layout diagrams of the chassis (see below). Note that each thicker blue line represents one inch, and each thin blue line represents 1/8 inch.

This is a view of the rear of the chassis, as if the rear wooden panel of the amp cabinet was removed. Obviously, a few components aren't sketched in. I haven't yet drawn the input jack or the pilot light assembly, nor did I draw the transformers or circuit board. Regardless, I am very satisfied with the placement of the tube sockets and the multisection electrolytic capacitor (that large thing right in the center). However, after seeing the layout from this angle, I decided it makes more sense to adjust the placement of the AC cord and fuse assembly. Rather than the way they appear in these illustrations, I am going to move the AC cord toward the baffle board by about 1.25 inches and scoot the fuse assembly to the left, placing it directly in front of the AC cord. This should make wiring easier, allow more space for transformers, and clean up the design a bit. To paraphrase Morgan Jones from the book, the more attractive the layout, chances are it will perform better.

Here is the bottom-panel component layout diagram. Not 100% sure about the placement of the speaker and vibrato pedal jacks yet. I plan to use this, once tweaked, to trace the cut/drill holes directly onto the aluminum chassis.

This is a partially-complete wiring diagram. The top portion is a nearly complete layout of the potentiometers, input jack, switch, and pilot light.

While so much of this may seem redundant and unnecessary, I honestly feel that the more I can do ahead of time, the more headaches I will prevent later.