Thanks for checking out my blog! This page is intended to provide tips and photos for others who are thinking about or in the process of hand wiring a tube amplifier. The amp I wired here is a Weber 6A20 Kit, which is a Fender Deluxe Reverb (AB763 Blackface circuit). Please feel free to contact me with questions or feedback.
It took a couple of weeks of researching kits and amp types before I made a decision on what to build. I also considered whether or not I should build and wrap my own cabinet, but in the end I decided to spend more energy on getting the wiring right for my first project. Ted Weber's kits are affordable with a lot of options to customize the cabinet that they build for you. I chose the 6A20 Amp Kit, which is the Fender Deluxe Reverb circuit.
The AB763 is not a quick build and requires patience and a lot of wiring. If you're not sure of what you're getting yourself into, I'd recommend starting with a simple circuit like the Fender Tweed Champ. I want to thank Rob Robinette for all of the great information he has shared on his site. I wouldn't have undertaken this project alone without his site as resource. I want to emphasize that working on tube amps can be dangerous. Please work safely and reference multiple sources when starting a project like this.
Weber had a Memorial Day sale, and I ordered the 6A20 kit for $590 after tax.
The cabinet that I customized with my Weber kit looks great, and I couldn't be happier with it.
After scouring blogs and forums, looking at recommendations from Rob Robinette's site, I came up with a list of tools for the project. Everything in the picture set me back around $250 ordering from Amazon...yikes.
Used Weller WES51 Soldering Iron
I did a lot of research for the iron because this was the most expensive tool. I figured going with a better iron would make learning to solder well less frustrating, which is worth a little extra money. It looks like the Weller WES51's are worth something if they're kept in good condition.
Used Proster V99 Multimeter
I saw so many people say that Fluke makes the best meters, but those were too expensive for me. I got one that is auto-ranging and that measures capacitance.
Hakko Tip Cleaner - This worked well and was glad I got it.
Tip tinner - Didn't use this.
Chisel tips - Only used the medium sized chisel tip and didn't need anything else.
Solder sucker - Worked great.
Solder wick - I felt the solder sucker was easier to use.
Flux pen instead of the paste - Didn't use this much, but probably should have.
Small needle nose pliers - Necessary.
Wire cutters - Necessary.
Heat sink clip (so that heat doesn't fry a component) - Didn't use this.
Alligator clips - Used a clip a few times to hold down a component when soldering.
Helping hands with magnifying glass - Very helpful.
Great 2-part video series on how tube amplifiers work.
Helpful 2-part video on how amplifier tubes work with a little bit of history.
Triodes are tubes with 3 main components: cathode, control grid, and plate (anode). As the cathode is heated, electrons fire towards the positively charged plate. When the guitar signal passes through the control grid, an AC signal is generated as electrons pass from the cathode to the plate. Triodes are good preamp tubes because they don't add bad harmonics to the signal and they have low distortion. The downside is that they have a low amplification factor. The 12AX7 is dual triode tube, with two triodes in one tube.
Beam tetrodes have a cathode, aligned control grid & screen grid, plate, and two beam confining plates. The screen grid and beam plates allow for higher amplifier factors because the electrons more efficiently pass from the cathode to the plate. The 6L6 power tube is a beam tetrode.
The Weber kit came with a pre-drilled chassis, though I later found out that some of the holes didn't line up or weren't quite large enough. I ended up enlarging holes for the main fiber board, the reverb driver, and speaker jacks. I also had to drill a new hole for the bias pot because it got in the way of the vibrato pots using the existing hole. I recommend fitting all of the components into the chassis before screwing things down or wiring inside of the chassis. I had to take a drill to the chassis later in the process when other components were already installed. Not ideal... Notice that it comes with a nice center tap grounding lug. I included a picture I found online that shows where components fits into the chassis.
The wood contraption is a stand that I built using a cheap fence picket from Home depot with some screws I had lying around. I saw photos online for similar stands and put together my own in an hour or so.
Before doing any wiring, I went to a FedEx store and printed off a few 11x17's of the Weber layout and schematic for the 6A20. I also printed off the original Fender schematic and layout for the Fender Deluxe Reverb as a second reference point. This turned out to be useful a few times when I was confused by a color or annotation in Weber's layout.
After setting up the chassis stand, I didn't know what where to start on wiring. I got on the internet and found out that there were a couple books with potentially more detailed instructions than the handful of existing forums and sites. Gerald Weber's "All About Vacuum Tube Guitar Amplifiers" had a brief chapter that outlined steps for building an amp from scratch, which didn't end up being very detailed but was enough to get me going. Weber (author) suggested starting with the heater circuit. It was good to be told that the heater circuit isn't fully included in the layout or schematic. Here is what I ended up doing:
At first I didn't even know which wire color I should use for certain parts. I had blue, red, yellow, and some black and white speaker wire. I planned to use blue for ground, yellow for audio signal, and red for hot DC though I started running out of certain colors toward the end. You'll see that in the heater circuit I used blue and yellow.
After wiring the heater circuit and pilot light, I decided to tackle the filter capacitor board. AC power from the wall enters the power transformer where it is converted to DC and smoothed out by the rectifier and filter capacitors. I was careful to assemble everything in the right orientation, knowing that the board gets mounted upside-down, with leads threaded up into the chassis. It's also important to remember that the filter capacitors are polarized and need to be installed with the positive dimpled ends facing the resistors.
This is a picture of the bias board. There is a tiny polarized diode that I had backwards the first time I installed it. I'm glad I double checked my work before moving on.
Wiring the main board was enjoyable and not as difficult as I expected. The hardest part was being sure that I was using the correct resistor and capacitor values. All of the capacitors and resistors came together in one bag and had to be separated by value. I'm not very good at reading the color bands on resistors so I used a multimeter to measure each resistor value to be sure I was using the correct one. Measure twice (or three times) and solder once. I also had to think about how I was going to wire the board into the other components once it was installed. I did as much wiring as I could before installing the board into the chassis. I made sure to label some of the wiring knowing it would make things easier when I got to the next step.
There are wires that runs across the board between components. I ran all of these below the board, but I've seen pictures of other projects where some of these wires are running above. I can't think of why it matters except that it would be easier to access the wires from above if something needs to be checked or changed. I would probably do it differently next time. Make sure that the leads coming off the board are long enough to reach other components once you're ready to install the board into the chassis.
After wiring the main board, I installed into the chassis and started wiring it into the rest of the components.
I scoured a lot of websites and forums trying to decide on a grounding scheme. I ended up sending the high voltage grounds to the ground lug in the chassis and used a copper bus bar for the preamp grounds. I grounded the reverb I/O and pedal jacks to the each other and the chassis. I went ahead and installed the brass plate that came with the kit, but didn't wire any grounds to it--the plate has been known to corrode over time. I read that some people would wire the back of the pots to each other with the ground bar, but I opted to float it so that changing pots in the future would be easier. There was a possibility that floating the ground bar makes the amp quieter as well. I didn't wire the bus bar to the chassis ground lug. Instead, I wired it just to the guitar input jack grounds which are connected to the chassis. Some said to drill a hole in a chassis near the normal channel input jacks, but I didn't feel this was necessary. I made sure to test my grounds with a multimeter, and I used Yellow Jacket GFCI when turning the amp on for the first time. I've also continued to use the Yellow Jacket in case something gets rattled loose as an extra layer of protection. The amp sounds great and the grounding is nice and quiet.
I did most of the wiring for the pots and jacks outside of the chassis by screwing them in backwards, and this made it easier. There isn't a lot of space in the chassis once they are installed. I put the bias and vibrato pots in earlier when I setup the bias board. I was worried about space and had to drill a new hole for the bias pot.
Finishing all of the wiring was a great feeling, but turning on the amp took some time and planning. It is recommended that you have a variac and/or a light bulb limiter for the first startup. I didn't have a variac and didn't want to buy one, so I wired a homemade light bulb limiter with parts from a hardware store and instructions I found online. Make sure you pay attention to polarity when wiring up the light bulb limiter. I made a mistake and tripped a fuse the first time I tried to plug it in. I should have checked my work more carefully with a multimeter before plugging it in.
The startup procedure Rob Robinette outlines involves turning on the amp in different stages to limit possible damage from wiring errors. It is also possible to have bad tubes or components, and this process would make it easier to troubleshoot where a problem is in the circuit. One step of the process directs you to turn the bias pot so that the tubes are cold during startup. This made the amp sound terrible when I got to the point where I plugged in a guitar. I was worried I had a problem, but when I biased the amp, everything sounded great. I'm proud to say I had no errors to correct--a great engineering moment!
Rob Robinette's site has some helpful information on biasing. I had never biased an amp before, and it was a difficult step for me. I felt that I wasn't getting accurate voltage readings from my multimeter. When probing the socket pins with the multimeter leads, the voltage would fluctuate up and down making it hard to know the exact bias current. I labored over this process for over an hour until I got to a point where I was comfortable enough to call it finished. Good luck, and let me know if you have any tips. Also, be careful. This might be the most dangerous step since you're probing an amp that is powered on. I created a couple of arcs while doing this because space is tight in the chassis near the tube sockets.
A picture of the reverb tank installation is included. I read that putting a piece of cardboard underneath the tank reduces feedback, which I can say is definitely needed if you don't put the tank into a vinyl bag. I still get some oscillation when I turn the reverb up past 5, and I'm planning to get a reverb bag to reduce this. The finished amp looks and sounds great though! I'm going to play it for a few months before I start thinking about all of the mods and upgrades that are possible.