UralTone 5F1 Champ 2.1 - Build Guide

UralTone 5F1 Champ 2.1 - Build Guide

The Champ 5F1 is one of the most legendary guitar amplifiers of all time. And for good reason: its simple construction and signal path allow for excellent dynamics and bring out the nuances of playing very well. Version 2.1 of the UralTone kit is a further developed version of the improved 2.0 version. A power supply choke has been added to the kit, filtering out the hum typical of the Champ circuit.

Structurally, the Champ is fairly simple, and even a beginner can assemble it, as long as care is taken and this guide is studied thoroughly before starting.

This article goes through the main stages of the build process. Not every single detail is shown in photographs, but each work step is explained in text. The purpose of this article is both to familiarize you with the build before getting started and to serve as help during the work. Study the pictures and instructions carefully before beginning the build. This will give you a good understanding of the type of work involved.

When building, always follow the layout diagram and parts list supplied with the kit. We occasionally update the wiring of the kits, and over time there are always improvements or changes, for example according to component availability. Minor differences from the photo series are possible. The layout diagram and parts list included with the kit are always correct and made for that specific version.

The layout diagram and parts list also serve as a build log. Always mark each installed component or connected wire on the parts list or layout diagram. This way you can make sure that all parts have been installed and all solder joints completed.

UralTone Tweed Champ 2.1 Parts List - BOM

UralTone Tweed Champ 2.1 Layout

Measurement Instructions

Soldering Instructions

Identifying Components

Always first check that all parts are included in the delivery. If you find anything missing, contact us by email or via the "contact us" form on the website. Please note that the components may look slightly different from those in the photographs. Also note that the voltage ratings of the parts may be higher than what is listed. We aim to keep the component models the same, but due to poor availability we sometimes have to change the manufacturer or model of a part. So if a component is a slightly different color, don’t be alarmed—each component has the required values marked on its body. Read the notes in the parts list carefully.

The amplifier build consists of three stages: installing the parts mounted to the chassis and wiring them together, populating and soldering the eyelet board, and installing the eyelet board into the chassis and wiring it up. The first two can be done in whichever order suits you. However, we recommend following the assembly order shown in the pictures below. This keeps the build organized and paced according to the structure of the article.

Construction begins with the parts mounted to the chassis.

Install the rear-side parts:

• PG9 cable gland for the mains cable
• 1x Noval socket (preamp tube) – note the socket orientation: the gap between pin 1 and pin 9 points to the four o’clock position in the picture. Mount using M3x6 or M3x8 screws. (Length according to the BOM)
• 2x Octal sockets (power tube and rectifier tube) – note the mounting orientation: the guide slot in the center of the socket (between pin 1 and pin 8) points to the two o’clock position. Mount using M3x8 screws.
• Speaker output jack.

It is best to leave the fuse holder uninstalled at this stage.

The same work step viewed from inside the enclosure.

Install the small parts on the top plate:

• 3x rubber grommets
• 2x M3x10 standoffs, mounted with M3x6 screws. The left standoff should be positioned at the left edge of the elongated hole as viewed in the picture. (You can use the eyelet board as a template during installation.)

The same work step viewed from inside the enclosure.

Mount the output transformer (right) and the choke (left) to the cover using two large-head M3x8 screws. Feed the transformer leads through the rubber grommets.

Note: The appearance of the choke may differ from the one shown in the picture.

Tighten the power transformer screws before installation if necessary.

Note: the transformer is inserted through the enclosure without disassembling it and secured separately with individual nuts.

Secure the transformer using M4 nuts and large washers. Note the installation orientation: the brown and blue wire pair should face toward the outer edge of the enclosure (to the right in the picture).

Transformers installed. The power transformer’s own mounting nuts remain on the outside of the enclosure.

Install the front panel parts:

• Power switch
• Pilot light socket. Try to tighten the socket nut carefully. This way the pilot light lens can later be unscrewed without the nut first loosening on the inside. This makes it possible to replace the pilot lamp without opening the enclosure.
• 2x potentiometers (Tone / Volume, values according to the layout diagram). The locating tabs must be removed from the front of the potentiometers. These snap off cleanly by twisting with pliers.
• Input jack.

The front panel stays in place with the help of the parts mounted to it. It is best to start installation with the input jack and pilot light so that the panel aligns correctly. Installing the pilot light is easier when there are no other parts next to it.

The same work step viewed from the inside.

Note: Contrary to the picture, install the pilot light socket rotated 90° counterclockwise. The socket is rotated later in the photo series, and the rotated position is shown in the layout diagram.

The build has now progressed to the stage where it is time to heat up the soldering iron. In the following steps, the transformer leads and the mains cable will be soldered.

Strip approximately 30 cm of the outer jacket from the mains cable.

Stripping the cable is precision work. Avoid cutting the insulation of the conductors inside. One effective technique is to bend the cable sharply and cut gradually deeper little by little. As the jacket becomes thinner, it will split open once the cut is deep enough. Rotating the cable and continuing the same way allows you to cut around the jacket more or less completely. If the insulation of the internal conductors is damaged so that copper strands become visible, cut off the damaged section and shorten the cable, leaving a fresh 25–30 cm length.

Feed the stripped cable through the PG9 gland and tighten the connection.

First, solder the wiring on the input side of the power transformer.

• Solder the blue wire of the mains cable to the power switch. Before soldering, slide a 2 cm piece of heat-shrink tubing onto the wire. After the solder joint is made, move the heat-shrink tubing into place.
• Route the yellow-green (YE-GN) wire along the front panel of the enclosure and shorten it as needed. Crimp a ring terminal onto the end of the wire and solder the connection. Fasten the terminal to the amplifier chassis using an M4 screw and nut.
• Install the fuse holder into the enclosure.
• Shorten the brown wire of the mains cable and solder its end to the fuse holder.
• Use the remaining brown wire for the connection between the fuse holder and the power switch. Protect the joint with heat-shrink tubing.
• Solder the red-red wire pair from the power transformer to the power switch according to the layout diagram.

The same work step from another angle.

Solder the leads going to the rectifier.

• 5Vac wires to tube socket pins 2 and 8.
• High-voltage anode supply wires to socket pins 4 and 6.
• The white and black shield wire of the B+ output are left unsoldered for now.

Solder the 6.3V heater wires to the inner holes of the pilot light solder lugs. Make sure the solder does not form a short circuit to the lamp body between the insulating plates.

Solder the leads from the output transformer.

• Solder the green wire to the power tube socket.
• The red wire is left unsoldered for now.
• Black wire to the sleeve contact of the speaker jack. Strip about 2 cm of insulation so that you can continue the same run to the middle switch solder lug of the jack.
• Depending on the speaker impedance, solder the desired output wire to the tip contact of the jack. The 8-ohm output is selected in the picture.
• The yellow 4-ohm output (if it is not selected and soldered to the jack) is left unsoldered for now.

Note: regardless of which output impedance you build the amplifier for, it is worth leaving enough slack in the transformer leads so that either 4Ω or 8Ω wiring can be implemented later.

The work on the amplifier chassis is now complete for the time being, and it can be set aside for a moment.

The next work step is populating and soldering the eyelet board.

Start by mounting the smaller resistors onto the board. The orientation of the resistors does not matter. Solder the parts in place at those points where no additional components or wires will be installed later.

Continue with the taller components. A few notes:

• The power stage cathode resistor (R11 - 470 ohm / 5W) should be kept away from the capacitor installed in parallel with it (C3). Heat ages the capacitor.
• Electrolytic capacitors (C3, C4, C5, C6) have a defined polarity. Their positive terminal is marked by a groove on the body. Align the groove according to the markings on the board.
• Plastic film capacitors (C1 and C2) can be installed either way around. If you install the optionally available PIO (Paper In Oil) capacitors, note their orientation according to the layout diagram. The body of these capacitors is live, so it must be placed on the non-energized side.

Solder the capacitor used in the choke wiring over the position reserved for R99 (R99 is not installed and may remain under the capacitor). Install the resistors and solder about a 10 cm piece of red wire to the same pad as the capacitor and resistors. You may also solder the black grounding wire as shown in the picture.

Shorten the black and white wires coming from the power transformer (shield, B+ CT) and solder them to the pad for the negative terminal of C6. This step is easier to do before the board is installed in the chassis.

Attach the eyelet board to the enclosure.

Solder the leads from the output transformer and the choke

• Yellow 4-ohm wire to the eyelet board. (This wire comes either directly from the transformer or from the jack lug, depending on the selected impedance.)
• Red wire to the eyelet board together with the second lead of the choke.
• The other choke lead, and from the same point a red wire to the rectifier tube socket.

Solder the remaining rear-side wires from the eyelet board to the tube sockets.

• Five wires from the preamp tube to the eyelet board (pins 1, 2, 3, 6 and 8).
• Three wires from the power tube to the eyelet board

Keep the wires reasonably short and away from each other. Route the wire along the surface of the enclosure.

Note: In this circuit, all white wires carry signal to the tubes. These runs are the most sensitive to interference. These wires should be routed along the surface of the enclosure unless otherwise stated.

Solder the front-panel-side wires as well as the capacitors that are soldered to the potentiometers. Also solder the wire running from the center lug of the volume potentiometer to the preamp tube. This wire should be as short as possible. If it is too long, it can easily cause oscillation, and the amplifier will then sound bad.

The wire run from the volume control to the preamp, seen from the other direction.

The heater wiring is critical to building a successful amplifier. The wire must be twisted carefully to minimize interference. A loose or uneven twist leaks interference into the signal, unlike one that is done carefully. For this reason, this guide includes several pictures and steps for the heater wiring.

Cut the solid-core green wire supplied with the kit into two equal lengths. Solder the end of one wire to preamp tube pins 4-5 (bridged).

Solder the other wire to preamp tube pin 9.

Twist the wires far enough to reach the power tube socket and bring the ends to power tube socket pins 2 and 7.

Solder the wire coming from the preamp tube to the pin 2 solder lug (the lower / foreground lug in the picture). Insert resistor R14 into socket pins 2 and 8, and the heater wire into the upper pin 2 solder lug. Solder pin 2. Do not yet solder the end of the resistor at pin 8.

Insert resistor R13 into the upper solder lugs of pin 7 and pin 8, and solder pin 8. Leave pin 7 unsoldered for now.

Solder the second heater wire to pin 7 and continue twisting the wires.

Twist the wires far enough so that the twisted pair reaches the pilot light. Solder the wires to the outer solder lugs of the pilot light.

Finally install the pilot lamp and its lens, as well as the potentiometer knobs. The amplifier assembly is complete.

Next, follow the layout diagram and check that all wiring has been completed and that all components are installed correctly. Take plenty of time for this inspection.

An updated inspection and measurement guide can be found here:

https://docs.google.com/spreadsheets/d/1CRP6kfBlP8VWHthzhgFmR605qaoRH0X6vjR967P3Yy4/edit?usp=sharing

First go through the instructions on the front page and then find the more detailed measurement instructions on the amplifier-specific tab. Turn all pots to zero.

Once the checks have been completed successfully, power can be applied to the device. Install the fuse and rectifier tube, but leave the other tubes uninstalled. Measure the voltage between ground and the power supply capacitors C4-C7. With no load, the voltage at all positive terminals will be approximately the same and at this stage clearly higher than the values marked at the test points on the layout diagram. If at this stage there is no voltage on the capacitors, the device smokes, sparks, or does anything unexpected, switch the power off.

Before any troubleshooting, confirm by measurement that the power supply capacitors (C4-C7) are discharged and that the device is disconnected from the mains. The layout diagram also includes AC voltage test points. These can be measured if necessary with the multimeter set to the 1000Vac range if the device has problems. Test points marked with one arrow are measured with respect to ground, while those marked with two arrows are measured between the arrows.

Install the remaining tubes and connect a speaker or dummy load to the output. Power up the unit. Let the amplifier settle for a moment and measure the voltages at the test points. At the same time, observe that the amplifier does nothing unexpected. Adjust the bias according to the instructions.

The layout diagram and inspection guide mark test points such as 400V, 325V, etc. The values of these test points are measured with respect to ground, meaning the black probe of the multimeter is connected to the chassis and the measurements are taken with the red probe. You can even sit on your other hand while doing so. Use the 1000Vdc range and allow approximately a 10% deviation from the stated values. 

The voltages at the test points are always affected by variation in tube parameters and differences in current consumption. Another factor that changes the results is the mains voltage level. This may vary between 220–240Vac, which is easily visible in the measurements. It is better to look at the voltages as a whole and allow some drift in either direction. Large deviations at a single test point while the others are correct may reveal, for example, that the wrong resistor value has been installed at that point in the circuit. It is also worth trusting your ears: if the device sounds bad, something is wrong.

Note: If you measure voltages without the tubes installed, the voltages from the power transformer with no load will always be higher. Apart from the AC measurements on the power transformer, always measure the voltages at the test points with the tubes installed.

Once the measurements have been completed satisfactorily, the amplifier is ready to be installed in its cabinet.

We wish you many enjoyable moments with your new amplifier!

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Troubleshooting

Sometimes mistakes happen during a build and the finished device does not work as intended. We have prepared troubleshooting instructions in which we go through both fault-finding techniques and the most common mistakes we have seen over the years. Below is a link to the article:

Troubleshooting Tube Amplifier Kits