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Interview: Boutique Amp maker Daytona Dave – Soldering and Circuit Building Safety

on , modified 29 May, 2013

DIY guitar amp kit: soldering

In the final installment of Max’s interview with Daytona Dave of Boot Hill Amps, Dave provides soldering and safety tips for DIY amp builders.

  1. Part One: Getting Started
  2. Part Two: Tube Bias and Speaker Selection
  3. Part Three: Soldering and Circuit Building Safety

Better Soldering for Beginners

Any tips to improve soldering techniques?

Get the best Soldering Iron you can afford. Get it good and hot, especially if it’s cheaper, leave it on for a good 10 minutes so that it’s properly hot. And if it’s your first time, practice on some bits of wire. Get some flux, even though most solder has flux in it, a little extra flux helps it flow, it’s an acid that cleans the metal and prepares it for bonding. Here in the States we can still get leaded solder, which is a lot better to work with.

“Your soldering iron tip needs to remain smooth and clean; you can use a wet sponge to clean it before you make each joint.”

When you make a good joint, it’s almost magical when the solder flows into it. It looks like the solder is almost being sucked into the joint. The cooled solder should also look shiny and smooth. If it has a dull colour, or a lump, that’s what’s known as a cold solder joint. Another way to check is to pull on the wire a little, and, if it pulls out it was a bad joint.

Your soldering iron tip needs to remain smooth and clean; you can use a wet sponge to clean it before you make each joint.

What are your 5 essential tools for building an amp?

  1. A good Soldering Iron, of course.
  2. Various types of small pliers – needle-nose, haemostats, etc.
  3. Small screwdrivers – Philips and flat-head.
  4. You need a few wrenches (spanners).
  5. A multimeter – to check your voltages to make sure they’re consistent. They can also be used to check continuity within the circuit and to find faults by checking for weak points. Incidentally ground = 0 volts.
  6. You should also have a pair of chopsticks – You can use them to poke around inside the amp instead of using your finger.

So, it’s not really tool-heavy. Making guitars requires a lot of expensive tools, to make them look good. But with amps, you need about $100 worth of tools and you’re fine.

Circuit Building Safety with Daytona Dave of Boot Hill Amps

What are some important safety tips?

If you’re poking around inside an amp, with chopsticks or with a probe from a multimeter, you should always have one hand behind your back or in your pocket. Now, the other probe from the multimeter will be clamped to ground, ground could be anywhere on the metal chassis. Of course the amplifier should be unplugged before looking for ground. Once you have ground you can plug it back in, and with the one hand behind your back, you can then use the red probe to check voltages with your other hand. Now the reason for keeping your one hand behind your back is, if you’ve got both hands inside a live amplifier – a huge no-no – your arms can act as a bridge though your chest, across your heart. So the voltage will go in your one hand, across your chest, through your heart and out the other hand to make ground. Voltage is always looking for ground, and it’s always looking for the quickest and easiest path. So you don’t want that to be your body.

A high voltage can also go through your fingers and down through your feet, into the floor; so another important safety precaution is to wear rubber soled shoes or to work on a rubber matt.

Within the amp you’ve got both AC and DC voltages. And you can’t go looking for AC voltages when your meter is set to DC, you’ll get an erroneous reading. So you need to know what kind of voltage you’re looking for. The heater voltage is normally AC, which is low voltage.about 6.3V. And most of the high voltage after the rectifier is DC.

A DIY amplifier from Boot Hill boutique amps

Another safety concern is with the capacitors and how they hold a charge. Capacitors are the larger bodied components, and they’re designed to retain current, and then release it, like a battery. If an amp is working properly, when you turn the amp off, the hot tubes will use up the remaining energy within the capacitors. That’s under normal conditions. If you’ve ever played your guitar through a tube amp, and then turned it off, you can hear the sound fading away, that’s the tubes draining the charge from the capacitors. There’s an old wives tale that if you strum your guitar when it’s turning off, that helps to discharge the capacitors, but they will actually discharge anyway, strumming the guitar just allows you to physically hear the power being drained.

“…you go sticking your fingers in there, that’s when you can get zapped.”

But, there are cases when the capacitors will not discharge, and this is when the amp is not functioning correctly. If the tubes are not heating up properly, a heater circuit is not working properly or something is miss-wired, the tubes will not be moving any current; so the capacitors are being charged by the power transformer, they reach their maximum voltage setting of around 350V – which is a lot of voltage – and you go sticking your fingers in there, that’s when you can get zapped. Even if it’s unplugged.

So, let’s say the tubes aren’t heating up, but the power transformer has sent voltage to the rectifier, the rectifier has put out that powerful DC, the capacitors have been charged, and there’s nowhere for that charge to go. So what do you do now? They’ll hold that charge for several hours or more if not discharged.

The best way to discharge them is to make a tool out of a bit of wire and a crocodile clip, but there’s a fast way to do it, just take a piece of wire stripped on both ends. Put one end to ground, and the other to the positive end of the capacitor. And if it had a significant voltage, you’ll see a visible spark, and once you see that spark, the capacitor has been discharged. Of course, you should make sure the amp is unplugged. It is said that discharging capacitors that way isn’t great for them, but it’s better than being shocked!

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I can recommend a good book for beginners to get advice on safety and general tips: Vacuum Tube Guitar and Bass Amplifier Servicing. The author is Tino Zottola. He’s got another book about building and understanding the circuitry, called Vacuum Tube Guitar and Bass Amplifier Theory. There’s also a lot of stuff for free on the internet. Aiken Amplification, another place you’ll find all kinds of information, and you just have to dig through that.

When you first started, did you have any knowledge about working with electronics? Should someone have a certain level of knowledge before starting an amp?

Not so much, but I could do some household electrical stuff, and I can work on cars and motorbikes. So, a basic combination of electrical and mechanical skills. But tube amplifiers are very different from your average wall socket or light switch.

“There are a lot of old timers who have a lot of knowledge, and are sharing it for free on there!”

You should try to build some knowledge before you get into it. You could start with a pedal kit, you’re not gonna hurt yourself with a pedal kit; get some books, like I recommended, scour the internet for information, join forums like the one I mentioned, and just ask questions.

The internet is a great resource. There are a lot of old timers who have a lot of knowledge, and are sharing it for free on there!

What are the most common mistakes that people make when building amp kits?

Most common mistake is to be in a hurry, and try to rush the work. You need to take your time. You know if you’re building a model car, and you don’t give the glue a chance to dry, and you start painting it and all that, and it ends up coming out all skew and bent? It’s like that. You need to pace yourself, work on it a little bit, put it aside, don’t rush it.

Another is, if you’re tired, and working on it, you can make the wrong connections, or if your soldering isn’t up to snuff, you can make bad joints. The thing is, every connection is critical, if you make one wrong connection, it won’t work. But it’s like following a drawing, so if you can do that, then you can make it work!

Read The Rest of The Interview with Amp Builder Daytona Dave

  1. Part One: Getting Started
  2. Part Two: Tube Bias and Speaker Selection
  3. Part Three: Soldering and Circuit Building Safety

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