DIY – Is it for you?
If you’ve ever had to wait for your tube gear to be repaired, or wondered why techs’ charge so much money? Then you may have asked “Can I do it myself?” That’s very good question, but one with a number of different answers.
I grew up in an era where fixing things was a part of the weekly routine. The way things were built supported the idea that a user would want to conduct their own repairs. It was relatively easy to take things apart, look them over and reassemble them. Not so much today. One of the few exceptions is vacuum tube technology. Not to say it’s easy, but compared to a smart phone or computer, tube amps are pretty accessible.
But here’s the rub. Just because you’re a great guitar player or spend hours every week reviewing the latest trends in audio equipment, doesn’t mean you should actually work on it. DIY can happen on different levels and each requires certain skills, education and tools. I have no carpentry skills and can seldom cut a board in a straight line. It’s just not in my DNA and my DIY attempts with wood have all met with failure. My idea of woodworking is assembling something from IKEA. I pay to get carpentry done.
The first rule of DIY amp work is to know your limitations. The second rule is read, read, read. There is a mountain of information available via books and the internet. If you don’t like reading and studying the inner working of your equipment then stop now. Hire a qualified person to work on the gear while you develop your playing skills or read the latest audio journal. It’s not worth saving $100 on a repair bill if it means you could hurt yourself. Under normal conditions tube equipment poses no danger to the user. If it’s damaged, or you take it apart, it can be very dangerous. Working in and around vacuum tube equipment exposes you to high temperatures and potentially deadly voltages. This is why rules one and two, above, are so important. Safety is why you have to educate yourself and know your limitations. But what about the really simple basic stuff? There are things you can do with very little training. Routine tasks that you do just to keep your gear sounding good.
Let’s start with tubes. Most of the tubes in an amp can simply be pulled out and replaced. The exception is power tubes. Power tubes need to be properly biased for best performance and maximum life. The two biasing schemes you will encounter are fixed bias and cathode bias. If the output tubes are cathode biased then it’s just a matter of remove and replace. The circuit design takes care of the biasing under normal conditions. If you don’t know what bias system your power tubes use, then you need to find out before proceeding. Biasing in a fixed bias design is a task you may want to learn, but doing it right involves technical skills and the purchase of tools and test equipment. You can still save a lot of money and time by simply buying output tubes from a retailer that provides a current matching number, like thetubestore.com Perfect Pair System, and having them installed by a tech. If you record the tube brand and matching number then all you need to do is order the same tubes with the same matching number. You pay for the tech service only once. This same advice goes for carrying spare tubes. With this level of DIY work you can re-tube your amp any time you want. If there’s an accident and you break a tube, you can plug in your spare. You can also experiment with pre-amp tube substitution. For guitar players this is usually all the DIY they need. But let’s say you want to do more. What will you need?
In the most basic terms, you will need education, tools and test equipment. To do something simple like biasing your output tubes, you have to know electrical safety practices when working on high voltage equipment. You need the ability to examine an electrical circuit diagram and determine the location of the actual components in the equipment in front of you. Test equipment must be used to measure voltage and current, so you have to know how to use that equipment. Once you have the measurements completed, you have to perform calculations using basic math and something known as Ohms Law. The results of those calculations will give you the idle current and static dissipation of the output tubes. If the results are high or low, then you will have to adjust the circuit values to raise or lower the idle current. That takes you back to the circuit diagram, where you have to figure out how to adjust the current. On some equipment there’s a single control designed for this purpose, but often you have to remove a component and replace it with one of a different value. To do this you have to look at the circuit diagram, determine what components need to be changed, locate those components in front of you and replace them. And by the way, you’ll also need to know how to use a soldering iron and small hand tools.
There’s no need to be discouraged. If you can learn these basics, you’re well on your way to doing just about anything inside a tube amp. I can’t stress enough how important it is to get educated before you get started. Get a couple of books on the subject, there’s many of them out there. Aspen Pittman, Gerald Weber, Dave Funk and many others, have written guide books for people thinking about DIY and beyond. Learn tube circuits, how to read schematics and identify high voltage circuits. Once you’re comfortable with the circuits you can start doing things like changing the type and value of capacitors and resistors and actually changing your tone. Then there’s doing your own repairs.
Many people get started in DIY with an amp failure. The user finds a blown fuse so they open it up and look around and see something that doesn’t look right. They see that each output tube socket has something soldered across two of the pins. On one of them it’s a cylinder with coloured stripes, but on the other it looks more like a piece of charcoal. Hmmmm… could this mean something? A little research on the internet yields a schematic and a little more research tells them this is a screen grid resistor, and they’re important. You can see where this is heading. Advanced trouble shooting and diagnosis were not required in this case. Now let’s just assume that the user managed to change the burnt screen grid resistor. That also assumes they had soldering equipment and knew how to do the job without getting electrocuted. Remember, tube amps can hold voltages of several hundred volts for quite a while after being disconnected from power. The user has just performed a repair that saved them $100 and a couple weeks in the shop. This is an entry level DIY repair.
But what would happen if our user’s amp blew a fuse, but when the equipment was inspected, everything looked fine? If the tubes were replaced and it didn’t fix the problem, what then? Well, that’s a whole new level of problem that requires a lot more knowledge and the use of more sophisticated and expensive test and measuring equipment. It never ends. And that’s really the level you need to get to if you want to build your own equipment. Even if you build a kit, you may need a solid electrical skill-set to get it running. You can follow the diagrams exactly and do everything correctly but still have a failure when you start it up. Bad or mislabeled components can make their way into your parts box. You need work your way through the circuit taking measurements and testing components as you go. Eventually you find the problem, and the solution goes into the memory bank for next time.
I find DIY a very rewarding activity. If you get bitten by the bug, it can become a hobby for a lifetime or you could turn pro. Start small. Begin with learning how your equipment works and identifying the major components. Learn how to measure voltage, current resistance and capacitance. Learn Ohms Law and spend a lot of time thinking. Thanks for reading this short introduction to the subject. Please remember that safety always comes first. Know your limitations and read, read, read.