UT Vibro Champ with Reverb - Build Guide

UT Vibro Champ with Reverb - Build Guide

The smallest in the Blackface series, the Vibro Champ with Reverb offers the same features as the Princeton in a smaller size and power output.

The single-ended 6V6 tube output stage provides approximately 5W of output power, which is more than sufficient for home playing. Like all Blackface Fenders, the Vibro Champ is relatively easy to build due to its spacious enclosure. The kit is well-suited for both experienced and beginner amplifier builders.

This article goes through the building steps in considerable detail. Not all details are covered separately, and the purpose of the article is mainly to familiarize you with the building process before starting and to serve as a reference during the build. Review the pictures and instructions carefully before starting the build to get a good understanding of the work involved.

Always follow the layout diagram and parts list provided with the kit during construction. We periodically update the circuits of the kits, and over time, there may be improvements or changes, such as due to parts availability. Any deviations from the images in this guide are possible. We aim to add notes in the text of this guide where changes occur.

The layout diagram and parts list also serve as a construction log. Always mark the installed part or connected wire on the parts list or layout diagram. This helps ensure that all parts and solder joints are completed.

Before starting construction, it’s a good idea to check the version numbers of the parts list and layout diagram from the links below. If the documentation provided in the kit is from an older version, ensure you use the correct guide before starting the build.

UralTone Vibro Champ with Reverb - Layout

UralTone Vibro Champ with Reverb - BOM - bill of materials

UralTone Vibro Champ with Reverb - Schematics

Instructions for measuring and startup

Always first check that all parts are included in the shipment. If you find any missing items, contact us via email or through the "Contact Us" form on our website. Note that the components may look slightly different than in the photos. Also, note that the voltage ratings of the parts may be higher than those listed. We strive to keep the models of the components the same, but due to poor availability, we sometimes have to change the manufacturer or model of a part. So if a part is slightly different in color, don't worry, each component has the necessary values marked on its side. Read the notes in the parts list carefully.

Building the amplifier involves three stages: installing the parts to be attached to the chassis and wiring them together, assembling and soldering the circuit board, and installing the circuit board into the chassis and wiring it. The first two stages can be done in any order that suits you. However, we recommend following the assembly sequence shown in the images below. This way, the construction proceeds in a structured manner as outlined in the article.

Attach the components to be installed on the lid. Pay attention to the orientation of the tube sockets:

• For noval sockets (small), the gap without a pin points to the 4 o'clock position in the picture.
• For octal sockets (large), the slot in the center pin points to the 2 o'clock position.

Noval sockets are supplied either with a pre-attached shield base or without it. If the shield base is not pre-attached to the socket, remove it from the shield and install it stacked with the socket.
Note: In the picture above, the noval sockets do not have the shield base installed.

The same step viewed from inside the enclosure. The speaker jack (at the bottom of the enclosure) should be left loose or not installed at this stage until the front panel components have been mounted.

Install the front panel components. The front panel is placed between the potentiometers and other parts, and it is secured using the nuts and other hardware.

The potentiometers on the front panel have a small tab that prevents the part from rotating when tightened. This tab is slightly too tall. Cut the height of the tab by about half. Otherwise, the front panel may bend. Alternatively, the tabs can be completely removed.

The power switch is installed by adjusting the height of the nut inside the enclosure so that the switch sits at a suitable and neat height on the panel. A large star washer should be placed between the inner nut and the wall.

The same step viewed from inside the enclosure.

Contrary to the layout diagram, the pilot light can be installed sideways, making it a bit easier to tighten the nut (see the picture above). If installed this way, ensure that the soldering lug of the pilot light does not touch the amplifier's chassis. The pilot light nut is challenging to tighten, but it's worth the effort. If the nut is left loose and the pilot light cover is tightened, the nut inside the enclosure may come loose first when replacing the bulb. This would require removing the amplifier from the enclosure when the bulb needs to be replaced.

The jacks at the input can be assembled more easily by using an enclosure as an aid during installation. Attach the jacks as shown in the picture and solder the resistors in place. (Note: If you are using solder with a high flux content and it splatters a lot, protect the panel before soldering.)

Attach the transformers and the can capacitor to the enclosure and pass their leads through the grommets into the interior of the enclosure.

To install the mains transformer, insert the transformer through the enclosure without removing its screws. The kit includes four large washers and M4 nuts, which are used to secure the transformer to the enclosure.

If the mains transformer does not fit into its slot, you can slightly loosen the screws on the transformer stack to help the screws find their correct positions. Before securing the transformer, carefully tighten the screws/nuts on the stack.

The same step as seen from outside the enclosure.

Strip approximately 35 cm of the outer insulation from the end of the power cord provided with the kit. Be careful not to cut the insulation of the internal wires. Bend the wire at the cutting point into a tight 180° angle. Carefully score the surface of the insulation at the outer edge of the bend. The tight bend will cause the scored insulation to split at the fold. If the wire does not cut through immediately, score a bit deeper. Rotate the wire using the same technique until the insulation is fully cut through.

Note: If you cut the wire such that the copper of the internal wires is exposed, cut off the wire and start with a new length!

The crimped strain relief is somewhat challenging to install. You can find installation instructions here.

It’s advisable not to skimp on the length of the stripped section—once the strain relief is in place, it’s difficult to remove. It’s always easier to shorten the wires than to extend them.

Solder a ring terminal to the protective earth wire. The wire should not be shortened; it should be left at its full length. The idea is that if the strain relief fails, the protective earth wire is the last wire to disconnect. Neatly loop the protective earth wire and attach the ring terminal to the amplifier chassis. Use a star washer between the ring terminal and the chassis.

Also, solder the power transformer wires (5Vac and 325Vac) to the rectifier tube socket and the heater center tap to pin 8 of the power tube socket.

On the front panel side, solder the heater wires to the solder lugs of the indicator light. Leave the other holes unsoldered; the heater wiring will be soldered there later. Solder the brown and blue wires from the fuse holder to the power switch. The soldering should be done on the lower terminals as shown in the picture. You can make the installation easier by loosening the screws on the switch and rotating it so that the solder lugs are more accessible. Once the brown and blue pair is soldered, solder the wires from the power transformer. We recommend protecting the solder joints on the power switch.

Solder the neutral wires from the power transformer to the common negative terminal of the can capacitor. These wires can be left unsoldered for now, as another wire and a resistor will be soldered to the same lug later. The wire can be cut to length and stripped in preparation.

Solder the green wire from the primary side of the output transformer to pin 3 of the power tube socket, and solder the secondary wires to the speaker jack. Depending on the desired output impedance, solder either the 4-ohm or 8-ohm output wire to the tip solder lug of the jack.

Solder the black and green secondary wires of the reverb transformer to the RCA connector of the tank and the wires going to pins 3 and 6 of the reverb tube socket.

The work on the chassis is temporarily complete, and it can now be set aside while you proceed with the assembly and soldering of the circuit board.

The circuit board in the kit follows the same concept as many other UralTone kits. Components and wires share a common pad, which replicates the eyelet-board design used in vintage Fender amplifiers.

The assembly order is generally based on the height of the components, with the lower parts installed first. This approach ensures that the components stay neatly in place on the board when it's flipped over for soldering. You can solder the parts from either side: soldering from the top saves the effort of flipping the board, while soldering from the bottom keeps the board cleaner as any flux splatters remain on the underside.

Leave the pads unsoldered where a wire or another component will be soldered later (refer to the layout diagram). This makes it much easier to solder later when the pad is open.

Place and solder the carbon composition (or carbon film) resistors onto the board.

Place and solder the power supply's metal film (or metal oxide) resistors and the large 5W cathode resistor for the power tube onto the board.

Place and solder the ceramic and plastic film capacitors onto the board. These components do not have a specific orientation.

Place and solder the electrolytic capacitors onto the board. These components have a specified polarity. The positive lead of the capacitor is indicated by a notch on the casing (in the picture, this notch is at the bottom of the component). Align the notch according to the markings on the circuit board.

Attach the circuit board to the enclosure.

Solder the power supply wires:

• Black wire from the negative terminal of the can capacitor to the circuit board
• Three red wires from the can capacitor to the circuit board
• Red wire from the output transformer to the can capacitor
• 220k resistor (R88) to the can capacitor

Wiring between the rectifier tube, fuse holder, and can capacitor.

Solder the screen grid resistor wire from the circuit board to pin 4 of the power tube socket, and from there to pin 1 of the preamp tube V4. Leave the preamp tube wire unsoldered.

Note: In the picture, the wire intended for pin 4 of the power tube V5 is incorrectly soldered to pin 2. Follow the layout diagram.

A detailed view of the previous step.

Note: In the picture, the wire intended for pin 4 of the power tube V5 is incorrectly soldered to pin 2. Follow the layout diagram.

Solder the blue wires to the cathodes of the tubes.

Note: The red wire from the previous step is now correctly shown in the picture.

Solder the white wires to the grids of the tubes. The wires to the front panel side of tube V1 will be soldered later in the photo series.

Solder the brown wires to the anodes of the tubes and the green wire to the footswitch.

The same step as before, with the wires hidden under the chassis lip shown in the picture.

Solder the white wires to the front panel.

Solder the black grounding wires to the front panel. Install resistors R11 and R52. Solder these only at one end, where a black wire will be soldered.

Solder the blue wires to the front panel.

Note: R89 is missing on picture above on lugs of intensity potentiometer.

Solder the brown wires to the front panel.

Solder the green feedback wire from the speaker jack to the board.

Lastly, do the heater wiring, which runs along the tube sockets above them.

Cut the green heater wire provided in the kit into two pieces. Solder the ends of the wires to the first preamp tube socket at pins 4+5 (bridged) and 9. Twist the wires into a neat pair. Cut the wire so that you can fold the ends over to the next socket.

Twisting the wire pair is easier if the wires are pre-cut to the appropriate length. The length is roughly the distance between the centers of the tube sockets plus 4 cm.

Proceed with the twisted wire from one socket to the next.

At the power tube socket (V5), there are two solder lugs, making it easy to connect two wires. From here, continue the twist to the indicator light.

Route the heater wire along the corner of the chassis.

Solder the end of the heater wire to the indicator light socket.

Attach the knobs to the potentiometers and install the indicator light and its cover in place. Install the fuses into the fuse holders according to the values specified in the parts list.

The amplifier assembly work is complete. Next, follow the layout diagram to check that all the wiring is done and the components are installed correctly.

The updated inspection and measurement guide can be found here:

Updated Inspection and Measurement Guide

First, review the instructions on the front page and find the detailed measurement instructions on the specific tab for your amplifier. Turn all the potentiometers to zero.

Go through the circuit wire by wire, component by component, and mark each checked part on the layout diagram. Once everything is confirmed to be correct, measure the continuity of the grounding and rule out any short circuits in the power supply using a multimeter:

Measure on the resistance setting of the multimeter: Place one probe on any part of the chassis and check for 0 ohms resistance between the other probe and the negative terminals of electrolytic capacitors C1, C2, C7, C8, C9, C15, C18, and the negative terminal of the can capacitor.

Measure on the resistance setting of the multimeter: Check the resistance between the positive and negative terminals of the can capacitor. In this measurement, the resistance will initially be low but should settle to several hundred kilo-ohms. Be patient and wait for the multimeter to stabilize. A low resistance, zero, or just a few ohms may indicate a possible short circuit, which should be addressed before applying power.

Once the measurements and checks are successfully completed, you can power on the device. Install the fuses and the rectifier tube, leaving the other tubes uninstalled. Measure the voltage between the ground and the capacitors on the circuit board. The unloaded voltage on all the positive terminals should be roughly the same and significantly higher than the values noted on the layout diagram's test points. If there is no voltage at the capacitors at this stage, or if the device smokes, sparks, or behaves unexpectedly, turn off the power.

Before troubleshooting, ensure by measuring that the sections of the can capacitor are discharged and the device is disconnected from the mains. The layout diagram also includes AC voltage test points. These can be measured if necessary using the 1000Vac setting on the multimeter if the device has issues. The points marked with a single arrow are measured relative to ground, while those with two arrows are measured between the arrows.

Install the remaining tubes and connect a speaker or dummy load to the output. Turn on the power. Let the amplifier stabilize for a moment, then measure the voltages at the test points. Keep an eye on the amplifier to ensure it isn't doing anything unexpected. Adjust the bias according to the instructions. Note that the voltages on tube V4 are measured with the tremolo disabled using the footswitch.

The layout diagram and inspection guide specify the test points for 400V, 325V, etc. These test point values are measured relative to ground, meaning the black probe of the multimeter is attached to the chassis, and the red probe is used for the measurements. You can even sit on your other hand to be extra safe. Use the 1000Vdc setting on the meter and allow for about a 10% deviation from the given test results.

The voltages at the test points can vary due to the differences in tube parameters and power consumption. Another factor that can affect the results is the mains voltage, which can vary between 220-240Vac and will be reflected in the measurements. It's best to consider the overall picture of the voltages and allow some tolerance in either direction. Large deviations at a single test point while others are within range may indicate, for example, an incorrectly installed resistor at that point in the circuit. Also, trust your ears: If the amplifier sounds bad, something is wrong.

Note: If you measure voltages without the tubes installed, the voltages at the power transformer will always be higher when unloaded. Except for AC voltage measurements at the power transformer, always measure voltages with the tubes installed.

Once the measurements are satisfactorily completed, the amplifier is ready to be enclosed. This guide will not go into further detail on the enclosure process. However, here are a few tips:

The kit includes a DIY version of Fender-style reverb tank cables. Instructions for assembling these can be found here: Fender-style Reverb Tank Cable Assembly.

The speaker cable is also a DIY kit and is styled after those found in original Blackface amplifiers.

The reverb tank should be placed in a bag designed for the tank. This prevents reverb feedback. You can either purchase a pre-made bag or make one from the same tolex material used to cover the amplifier enclosure.