Troubleshooting DIY kits - tube amplifiers

This article is intended for hobbyists of kit tube amplifiers who have assembled a UralTone amplifier but the device still does not work properly. In this situation, it is advisable to proceed systematically. Most often, the fault lies in a wrong connection or poor soldering. New components are very rarely faulty, so do not suspect a component failure first, but check the connections and solder joints. In 99% of fault-finding cases, it turns out that it was a builder's mistake. It can be difficult to find one's own mistakes, and the eye can be blind to very obvious faults during inspection. Patience is key, and perseverance will be rewarded.

Don't get discouraged; in the end, the amplifier will be fixed!

Safety

Tube amplifiers have voltages that can kill you! Filter capacitors can hold up to 500VDC voltage after power is cut off.

• Remove the power cord from the wall well before going through the connections (except for voltage measurements). Unplugging the socket from the wall or disconnecting the IEC connector from the back panel of the amplifier should be a habit to do as the first step when the amplifier is turned off.
• Before touching components and other energized surfaces, ensure that the voltage of the power supply capacitors is below 10V. Measure the voltage from the terminals of the high-voltage capacitors with a multimeter, or if you cannot measure directly from the terminals, you can measure from the tube anodes (octal power tubes often pin 3, EL84 pin 7, ECC83 pins 2 and 6) and between the input jack or the chassis frame.
• You can speed up the voltage discharge by discharging the capacitors with alligator clips and a 100-220K 2W resistor. Connect the resistor using the alligator clips between ground (chassis) and the + terminal of the power supply capacitors and wait a few minutes. Always verify by measuring that the capacitors have discharged.
• Use the one-hand rule: keep one hand in your pocket, use insulated test leads, and avoid metal bracelets or watches.
• Always use the correct value fuse.
• The safety ground must always be connected to the chassis. Never disconnect the ground.

Typical Faults

• The value of a part has been checked from example photos, not from the BOM (parts list). Always check the values from the BOM and place them according to the layout image.
• Solder joints: cold solder joints, missing solder joints, or solder bridges between pads or pins.
• Wiring: a wire connected to the wrong pin, incorrectly routed ground.
• Component values: for example, confusion between 470 Ω and 470 kΩ.
• Polarity: electrolytic capacitor or diode installed backwards.
• Jacks and pots: connected in reverse or to the wrong terminal.
• Burnt wire insulation - In shielded wires, sometimes the insulation of the inner wire melts, causing a short circuit between the ground (shield) and the center conductor (hot signal wire).
• Burnt component casing - Melting on the side of a capacitor often destroys the capacitor.

Rarely is a faulty component the cause – in about 99% of cases, the reason is poor soldering, incorrect component placement, or incorrect wiring. This assumption of a faulty component wastes time that could be spent on checking what really matters.

Don't Do - Typical Fault-Finding Problems for Beginners

For 20 years, we have been responding to customer fault-finding messages, and one pattern repeats itself. Measurements have been started without knowing what to measure and how to analyze the measurement results. If you do not understand the operating principle of the circuit, it can sometimes be difficult to analyze the measurement results. Therefore, it is advisable to proceed with measurements according to the instructions. Other measurements often lead to confusion and do not help.

This is especially true when you are specifically looking for a fault location as efficiently as possible, rather than primarily learning about the device's inner workings. Here are a few examples:

1. Measuring resistances in the circuit - This is mostly pointless and does not provide information that helps move forward. When measuring resistance with components and wires connected, the entire circuit affects the result. You need to understand from the schematic what resistance should be at each point. For example, measuring the resistance of resistors when they are soldered in is often pointless because all surrounding components affect the result. The value of the installed part should be checked based on its markings, not by measuring.
2. Measuring the resistances of transformers or output jacks - In a transformer, the resistance of many windings is nearly zero. If you measure the resistance between the output jack's ground and hot solder lug, the correct result is under 1 ohm. This may seem like a short circuit, but it is not. The resistance of the primary winding of the output transformer may only be, for example, 0.2 ohms. This is difficult to measure with a multimeter, so avoid measuring it.
3. Suspecting that a part is faulty - Electronic components are almost never faulty when they come off production lines. Additionally, we select components for kits primarily based on quality. We have sold millions of components, so experience has taught us which manufacturers to use and which to avoid. It is extremely unprofitable for us to choose a part that leads to warranty returns, so we do not use parts that have known issues. Soldering can indeed damage almost any part, but this can often be detected visually (the switch housing is melted and the pin has shifted/bent, the component is charred, there is solder damage on the side of the component, etc.).
4. Suspecting that the component value is different from the value written on it - It is nearly 100% certain that the values indicated on the components (color code, written value) are correct and within tolerances. If you get a different result when measuring a resistor or capacitor, it is almost always a measurement error or the stated tolerance has not been taken into account. If the tolerance of a part is 20%, the stated value of 100 can therefore vary between 80 and 120, and the part is still perfectly fine.
5. Ignoring tolerances in voltage measurements - The voltages mentioned in the instructions are not a percentage game. Even variations in mains voltage can affect the B+ voltage by tens of volts. A 20% tolerance is often good, especially when searching for faults. If all voltages are within 20%, the device usually works perfectly fine.

Progressing in Fault Finding

1. Visual inspection
   • Check each solder joint and connection according to the layout. Go through all solder points systematically. Mark each checked solder point on the layout image.
   • Compare with the instructions: is each part in the right place, is the value correct, and is the installation direction correct?
2. Mechanical inspection
   • Gently tap different points with a wooden or plastic stick. If the sound changes or disappears momentarily, it is likely a bad solder joint.
3. Voltage measurements
   • Measure and record the voltages from the instructions in a measurement log. Compare the voltages with the readings in the voltage table from the instructions. If any voltage deviates by more than 20%, examine the components, solder joints, and wiring at the measurement point very carefully.
   • Deviations indicate where the signal is not progressing correctly.
   • If you are in contact with our technical support, report ONLY those voltages that deviate from the stated voltages. Always provide the target voltage and the measured voltage, as well as the point from which the voltage was measured.

Measurement Log (Example)

Record each measurement. This makes it easier to remember where the values deviate from the expected.

4) Symptom – Cause – Repair

Technical Support

If you have gone through everything multiple times, read this article, and followed its instructions, but still cannot get the device to work, you can contact our technical support via email. Please note: We cannot help via phone or at our physical shop: There may not be the right person available by phone or in-store who can assist with that specific device. There are also no documents available that are often needed in customer service (we have over 100 kits so we cannot memorize everything).

So please give us the opportunity to respond carefully and thoughtfully, meaning contact us regarding kit technical support only via email. When contacting support, always mention the following:

1. The exact model of the device (we have had tens of thousands of orders, so we cannot easily know which device is being referred to by name). Please mention the device and the problem, preferably also in the subject line of the message. This way, the message will be directed to the most relevant people.
2. When the kit was purchased (so we know approximately which version it is).
3. Is it a construction-related fault or has the device been functioning but has since broken down.
4. Description of the symptoms. For example, fuse blows immediately on startup OR the device works, but there is hum in the sound OR channel 1 works, but the distortion channel does not OR otherwise works, but the treble pot does nothing, etc.
5. A list of actions you have already taken regarding fault finding, deviations in the voltage chart, and especially confirmation that you have checked the position and installation direction of each component, the installation point of each wire end, and the cleanliness of each solder joint at least twice.
6. Do not send us all measurement results, ONLY those that deviate more than the allowed variation mentioned in the instructions (e.g., 20%).
7. We cannot verify the correctness of each part or connections from photos. Checking is the builder's responsibility.

Videos or recordings do not often help us to reply your email. If necessary, we may request recordings, videos or photos.

Summary

When a device assembled from a kit does not work, the cause is almost always a wrong connection or poor soldering -> builder's mistake. Go through the device systematically: check the connections and solder joints visually, measure the voltages, and compare them with the reference values. Keep a record of measurements and checked parts as well as solder joints. This way, the fault is usually found and fixed quickly. Always remember safety: mains-powered devices have deadly high voltages. Treat them seriously and with utmost caution.