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More than once I have asked myself what the most sensible way would be to allow DIY enthusiasts to build a good tube amplifier without spending absurd amounts of money. Building a unit completely from scratch can become expensive very quickly, especially if you want to use decent components, a well-made chassis and output transformers worthy of the project. On the other hand, the Chinese market offers assembly kits aimed at beginners, often sold at very low prices. Below are two examples.

There is a community of Chinese tube amplifier enthusiasts who genuinely appreciate these products and the results they can achieve. Some even claim that certain models sound as good as, or even better than, much more expensive equipment. In some cases this may actually be true, because the world of high-end tube audio is full of extremely expensive amplifiers built more around imaginative theories than sound engineering principles. A high price alone guarantees neither good performance nor good design.

That does not mean, however, that you can simply buy a cheap kit, assemble it as supplied and expect miracles. The interesting part, at least for those who truly enjoy working with electronics, is using these amplifiers as a mechanical foundation on which to build something better. Taking them apart, understanding them, modifying, correcting and rebuilding them is all part of the fun.

This article is not aimed at people who simply want to buy a ready-made amplifier, connect it to their hi-fi system and forget about it. It is intended for those who enjoy the building process itself, studying the circuit and making real improvements to the amplifier. In many cases it is not even about saving money – the journey itself is what makes it worthwhile.

If you want a Chinese tube amplifier to perform really well, replacing a couple of capacitors or installing a set of NOS tubes is usually not enough. In many cases almost everything has to be stripped out and a completely new amplifier built inside the same chassis. You keep the cabinet, some of the hardware, the tube sockets if they are decent, perhaps the power transformer if it proves satisfactory, and replace everything that genuinely limits performance. Yes, it is a demanding job, but for those who enjoy this hobby it is also a great deal of fun.

For this reason it makes little sense to criticize people who modify these amplifiers or dismiss the whole idea as something only “charlatans” would do. This is not simply about buying an amplifier to listen to music. It is about DIY construction, learning, experimenting and tube amplifier modding. The real satisfaction comes from transforming an ordinary product into something far more serious.

This approach is also an excellent educational tool. Rebuilding a Chinese tube amplifier allows you to understand in practice how vacuum tubes operate, what the transformers actually do, how much influence the circuit has on the final result and why apparently minor design choices can completely change the amplifier’s behaviour.

Personally, I make schematics, transformers and my experience available precisely to help anyone who wants to follow this path. There is absolutely nothing to be ashamed of in starting from an inexpensive kit, as long as you understand exactly what you are doing. It is a practical, hands-on and often highly educational way to enter the world of tube amplifiers.

One of the main obstacles for many DIY builders, especially beginners, is producing the mechanical structure. Making a clean, sturdy and accurately drilled chassis requires time, proper tools and a certain amount of experience. It is no coincidence that many interesting electrical projects eventually end up inside rather embarrassing enclosures…

Far better to modify a Chinese amplifier yourself than to buy something like this…

Poorly drilled boxes with even worse workmanship inside…

The idea is not limited to beginners. Even experienced builders may find it worthwhile to buy an inexpensive kit simply to reuse the chassis, hardware and mechanical parts, while completely rebuilding the electrical section. Take, for example, the EL34 kit shown in the previous screenshot.

For approximately €212, based on the exchange rate on August 30, 2020, it was possible to buy a kit containing a pre-drilled steel chassis, vacuum tubes, sockets, switches, mounting hardware, RCA connectors, speaker terminals and various small parts suitable for building a point-to-point wired amplifier without using a printed circuit board. Purchasing all these parts separately, or having an equivalent chassis manufactured, would easily cost more. That does not even take into account the time required for the mechanical work.

However, enthusiasm should be tempered straight away: achieving good performance from these amplifiers does not simply mean replacing a few tubes with NOS equivalents or fitting more expensive capacitors. The main limitations almost always lie in the transformers and the circuit design. In the EL34 kit, for example, the published schematic shows a 6N9P dual triode, equivalent to the 6SL7, driving the EL34. The two internal sections are connected in parallel, although that tube could probably have been used more effectively. It would also have been possible to evaluate using a single dual triode to drive both output tubes through a more rational design.

I do not want to sound overly critical, but I often see enthusiasts spending more money on NOS tubes than they originally spent on the entire amplifier. Some improvement may well be audible, but this kind of upgrade is unlikely to transform the amplifier into something significantly better. If the real limitations lie in the circuit or the transformers, even the most prestigious tubes in the world cannot perform miracles.

The most sensible approach, in my opinion, is to regard these kits as a starting point. You can buy the kit, discard the original transformers – or at least the output transformers – verify the quality of the power transformer and completely rewire the amplifier using a better designed circuit. Where appropriate, you can install higher-quality capacitors, a better potentiometer and components better suited to the performance you want to achieve.

It is true that such a modification may ultimately cost more than the original kit. However, if you were to build the same amplifier entirely from scratch, you would still need to buy the chassis, sockets, connectors, switches and all the other mechanical hardware. The real advantage is that these kits already provide most of the mechanical parts and a chassis that is drilled and ready to use. That saves a great deal of time, physical work and frustration.

Browsing these Chinese marketplaces, you can find a variety of assembly kits that make an excellent starting point for something much more serious. The only important point is to choose kits designed for point-to-point wiring rather than printed circuit boards. With PCBs, the tube sockets are often mounted directly on the board instead of the chassis, making major modifications much more difficult. Printed circuit boards are also poorly suited to larger components, such as certain high-quality capacitors.

The same principle applies not only to new kits but also to used amplifiers. Even a non-working amplifier bought cheaply can become an excellent mechanical platform for building something completely different. On the other hand, it makes little sense to buy an expensive new amplifier only to dismantle and rebuild it immediately. I will return to this subject in a dedicated article in the future.