DIY – Is it for you?

DIY – Is it for you? What you should think about before starting out

12:46 pm

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 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.

6 Responses

  1. Brian Lord
    Brian Lord at |

    Thanks John,
    Playing with a few amps now.
    Dead right and I’m a parky and electrical engineer.
    Great hobby though.
    A lost art!

  2. Chris Bridge
    Chris Bridge at |

    Hi John,
    I’m a technician that specialises in audio equipment repair, both the stereo audio system and guitar amplifiers. The biggest problem I see from DIY efforts are really poor soldering (you need a soldering station people, not a hobby iron with uncontrolled temperature!) and highly questionable circuit changes. Some technicians are horrible too, and some lay people are actually pretty good at this. Most are not.

    One major issue is the person repairing a home amplifier and reads about the “tube rolling” that one might do with an instrument (guitar) amplifier. Things said about tubes in musical applications cannot and do not apply to a home stereo amplifier. The designs are totally different between the two. I’m sorry I have to add the home amp angle, but it is a real problem in the stereo repair field.

    Back to guitar amplifiers. A good technician is your most important resource. He or she can look at an amplifier and see things that are either causing trouble now, or will be. They can take corrective action before it becomes an expensive repair. They can also save you from performing unnecessary work or highly questionable modifications. THe worst idea I ever heard was someone who wanted to change the tone stack on a Fender Twin Reverb to a Marshall type so it would sound like a Marshall. Huh? Buy a Marshall then instead of trashing a very nice amplifier! Then there are those who want to add a signal output so they can record directly. You can do this, but it often requires a signal transformer as many old chassis’ are wired to one side of the AC mains line. If they aren’t, you can still have leakage problems.

    So go ahead and DIY, but be careful to keep the job within your abilities. There is no shame if you stop and take it to a tech instead of trying to finish something. Doing this, and being honest with your tech will save you a lot of money over the years

    Most technicians are not out to get you for all they can (those people do exist), but rather most of them like to help people. Tell them what you like, or the sound you’re going for. They can often help. A long term relationship with a technician, or a few (’cause we aren’t all masters of everything, I’m not) will create a very positive experience. Don’t hesitate to ask to see their work bench. Many are justifiably proud of it. You want to see equipment in good repair and some organization. Also look at their work. If it isn’t neat, it is likely a disaster waiting to happen. The next good tech will be forced to clean it up, so there is an added cost to not doing things properly.

    1. John David McCormick
      John David McCormick at |

      All good points!

  3. Manuel
    Manuel at |

    Excellent Article. Really appreciate seeing this sort of stuff here. You folks are equally about spreading knowledge, not just another tube seller. A+++ on my last order, sounds amazing now! Thank You, Thank You!

  4. James Allman
    James Allman at |

    Nice to see your commitment to customer education! I started working on tube stuff at the age of 10, and it lead in to a career in the electronics industry, from repair and installation to selling instrument solutions from Hewlett-Packard/Agilent and Tektronix. Presently working on refreshing and updating my old Traynor YBA, and even with years of experience, I still review everything because even if you’re trained in the industry, there’s always little details to refresh, or leverage off those with specific experience. Life is a journey, don’t be afraid, but do your homework, especially when working with 4-500 volts DC. (Hey, even trained, I got zapped with 400 VDC in my early 20’s. When I came to, I had to get a ladder to pull my screwdriver out of the ceiling tile. And I had my left hand tucked in behind my back and an isolation transformer… My usual habit when working on live high voltage circuits.) It’s awesome to buy from a like minded company… So happy Chris Church pointed me your way!

  5. Chris Carson
    Chris Carson at |

    I just finished my Sunvalley SV-EQ1616D. You kinda have to build em’ if you want one. Now I built my first amp from a kit when I was 16, some 60 years ago, and I have good equipment, largely from building Quads for FPV.

    My son now carries on with Quads and has my stuff at his house as he smashes them constantly. Its part of the way real FPV quads are flown. 😉

    Anyhow my stuff was easily good enough to build the phono section, and I had it gone over by a friend who is an electronic tech and has test equipment. Absolutely stunning phono section, among the best there are. Now I’m happily tube rolling the sucker, and driving Victor mad. You will have to deal with Victor if want one. 😉


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