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.

More Arriving Everyday

The first round of parts from AmpWares arrived today. Even though they don't reply to emails very well and have slow shipping, everything arrived just as described.

Now that pieces are starting to arrive, I can get a better idea of exactly how to arrange them around the chassis for best layout and minimal hum.

I purchased a book called Building Valve Amplifiers by a Brit called Morgan Jones, and although it is primarily geared towards hi-fi stereo equipment, many of the tips and principles apply to guitar amps as well.

You can see in the photos some of the parts that have come in so far.

This is the chassis. It is 17" long, 4" wide, and 3" tall.

Here is the cloth-covered wire, fuse assembly, pilot light assembly, and Carling power switch, all from AmpWares.

These are the tube sockets from AmpWares. On the left are the octal sockets, one for the power tube (6V6GT) and one for the rectifier (5Y3GT). On the right are the 9-pin sockets, which will hold 12AX7s for the preamp section.

I have ordered the turret board and a few capacitors from Triode Electronics. I will post pictures of those parts when they arrive as well.

Tiny Bits Tedium

I would have never guessed that locating all the bits required would be so frustrating. Most of the larger parts are pretty easy to obtain, but some of these potentiometers and capacitors are out of production and/or very rare. 

I ordered most of the random chassis parts from AmpWares three weeks ago, and haven't heard anything. No shipment has arrived. No emails have been returned. I called today - I got a recording stating that the voice mailbox was full. But my credit card was already charged. We'll see how that one pans out. I am hoping Mr. AmpWares is just on vacation or something, because I had intended to purchase all the resistors and most of the capacitors from his site as well.

As for the vibrato intensity potentiometer, the schematic calls for a 25K ohm reverse audio taper. Apparently, this must be the most rare pot in the universe. I checked over a dozen other Fender schematics of amps that have vibrato circuits, and NO OTHER ONE to the best of my knowledge uses this pot. Most, at least after 1964ish, utilize a 50K ohm R.A. pot, and some of the older tweed models use a 3Meg or something. I suppose I could use a substitution, but the point of this exercise is to copy the Vibro Champ's schematic as closely as possible, since I am still learning electronics; if I stick to the Fender circuit, I'll have an easier time troubleshooting this prototype.

Another rare part seems to be a 2uF @ 25 volts electrolytic capacitor. I have found the other rare 25uF @ 25 volts el. cap (of which I'll need three) from Triode Electronics, and they also have a 10uF @ 25 volts cap which might have to suffice. I am waiting for a reply from the sales department.

Weber Speakers seems to be one of the most complete catalogs of electrical components for amps on the web, at least that I have seen so far. They make the exact multi-section electrolytic capacitor (filter cap) that the schematic calls for: 20uFx 20uF x 20uF x 20uF @ 450V. They even offer it in three varieties, the stock "twist-on" style, the screw-mount wafer base, and the screw-mount clamp. I think I'll order the clamp, as it seems to be the most rugged.

On a side note, I have been considering making this amp use a single 10" speaker rather than the dual 8" speakers I originally planned for. I guess we'll see how much money I can justify spending when I get to the baffle board-building stage.

Decisions, Decisions

Well, parts are beginning to arrive. I received the chassis yesterday. I went with the aluminum Hammond box. After searching the web for a decent price, I found the best price/shipping at Mouser Electronics. 

Now that I have the chassis, I can begin drilling holes and mounting components as they arrive. Before I just go tearing into this $24 piece of aluminum, I wanted to make sure I knew exactly what the control panel was going to look like. This way I can accurately place the holes for the shafts of the potentiometers and switches. The decoration and lettering might change a little before completion, but here is my current idea for the control panel:

Keep in mind that is a view of the top of the amp.

And speaking of drilling into expensive metal, I have discovered through much research that the best way to drill the large diameter holes for the tube sockets is going to be using a Step Bit (sometimes called a UniBit) and a drill press. The bit that steps up to 1" is about $30. Looks like a trip to the hardware store is in order.

Chassis Selection

Without doubt, there will be several aspects of this project that are going to be trial-and-error. That is the nature of DIY projects. However, I am trying to minimize the money-wasting aspects. One way I have found that helps is to build the project in your mind and on paper several times before you ever purchase or cut the first piece of material. 

This tactic is going to be invaluable during the creation of this amp, especially regarding the chassis design and cabinet construction. 

My previous sketches called for a chassis made from a 12"x8"x2" steel project box. I have since located a supplier for many more sizes and materials. My latest sketches include an aluminum box (also made by Hammond Manufacturing, the same company that makes the other steel boxes) that measures 17"x4"x3". After some sketching and figuring, this shape is much more conducive to this particular project. Also, aluminum doesn't rust, and comes uncoated/unpainted, which would prevent me from having to sand off the paint from the steel box at all points where an electrical ground would be attached. 

After doing some web-based research, I've discovered there is quite a debate over using aluminum vs. steel boxes for amp chassis. I sifted through post after post and finally concluded that either one should be sufficient, as long as I brace the section where the heavy power transformer and output transformers are to be attached with a stronger, thicker metal of some kind (which I'd already planned to do). The good news is that this new aluminum choice is roughly the same price, maybe a little cheaper than the steel counterpart. 

I'm working on drawing up some plans for the entire contraption, cabinet and all. I will post those pics as they are done. 

Preliminary Cabinet Design

I realize that I'm going to need to figure out what kind of cabinet I want to put this amp in before I can begin to assemble the chassis. Because of the style of project box I chose, it looks like it's going to be smartest to make a vertically-mounted chassis (like the old tweed Fender amps). I'm doing it this way for two reasons: because it's going to work best with the parts I've chosen, and because this way I'll have the opportunity to design and build my own style amp rather than completely copying the Vibro Champ. Pride in originality. Below is a sketch of what it might look like, from the rear:

As you can see, the chassis will sit vertically with the tubes protruding towards the floor. 

Another cost-saving feature of this arrangement will be the cover of the project box. Since it can be covered by the back (wooden) panel of the amp cabinet, I don't need to purchase the costly sheet metal cover to match the project box. 

At this point, I am fairly certain I'm going with a 2x8" speaker configuration. However, that can be decided for sure much later, after the amp chassis is assembled. As long as I'm pretty sure I want to make the chassis sit vertically like this, I don't have to make final decisions on speakers and exact cabinet size until later.

Parts List, Pt. 1

I've finally gotten around to finding most of the parts I need to get started. This list is not complete; I haven't included any of the resistors/capacitors or tubes yet. Basically this list gets the chassis rolling (so to speak), and it doesn't include any parts for the cabinet, either. 

Partial Parts List, Part One:

Power Transformer*          $35.00

Output Transformer*       $20.00

Circuit Board#                  $34.95

Power Switch                     $3.75

Pilot Light Assembly          $6.00

Potentiometers:

1. Intensity 25K Rev.Audio* $1.80

2. Speed 3.0M Rev.Audio*   $1.80

3. Bass 250K Audio*           $1.80

4. Treble 250K Audio*        $1.80

5. Volume 1M Audio*         $1.80

Input Jack (1/4" Mono)§       $.95

Tube Sockets:

1. Octal (2 qty.)                 $5.00 ea.

2. 9-Pin (2 qty.)                $2.50 ea.

Fuse Assembly 1A Slo-Blo   $2.50

Fuse 1 Amp Slo-Blo             $.60

Project Box (Chassis):

12"x2"x8" §                       $25.68

Wire: (6 ft. ea. color)

1. Green 18 ga.                   $.50/ft.

2. Black 18 ga.                    $.50/ft.

3. White 18 ga.                    $.50/ft.

4. Blue 22 ga.                      $.50/ft.

5. Red 22 ga.                       $.50/ft.

6. Yellow 22 ga.                  $.50/ft.

IEC Power Connector             $1.50

Total: (ex. tax and shipping)  $174.73

All parts from AmpWares, except:

* Weber Speakers

# Triode Electronics

§ Parts Express

If you need part numbers or more specifics, contact me. 

Vibro Champ Pics

Here are some photos of the amp I'm cloning:

Schematic & Layout

The first order of business is deciding which amp to clone. I have several tube amps, but my personal favorite has always been my 1968 Fender Vibro Champ given to me by my uncle. It is the best sounding 6 watts you will ever hear. Plus, I've had it open enough times to determine that the guts look simple enough to emulate on my first outing. 

Here is an image of the schematic obtained from Fender:

 

And here is the layout (also from Fender):

As you can see, this circuit uses two 12AX7 tubes for the preamp section, a 5Y3GT rectifier, and a 6V6GT output stage. Luckily, all of these tube types are fairly common and relatively cheap. A few of the capacitors are going to be hard to find, but with enough digging I should be able to find them.

Between the documentation and the advantage of having a real physical amp to look at, I think we have a pretty good chance of putting this thing together.

Let's get this started

Welcome! This blog is a record of my attempt to make a tube amp from the ground up. I am not an electrical engineer, but my partner in crime is. With my musician (and gearhead) background and his expertise, we hope to have fun and learn a lot along the way. 

As posts progress, feel free to add comments with tips, suggestions, cautions, and warnings. If all goes well, we'll have a working amplifier and we won't Shock Ourselves!