I’m on an ongoing mission to demystify some of the voodoo that surrounds discussions of tube guitar amps. Here at The People’s Amp, we’ve always been about keeping things simple, not buying into wacky ideas about specialty components, and maintaining transparency about what goes on inside a tube guitar amplifier. It’s interesting, as many players will have rigid ideas about what they want from an amplifier, whether they know what they are talking about in technical terms or not. Don’t get me wrong, I am not saying that there is anything foolish about having specific ideas about what you want from your amp, and we all have our own opinions and biases. As an example, I have always thought that I prefer amps with EL84 power sections, especially when they are overdriven. This might be true for me, and I probably will always play an EL84 amp, as a simple matter of taste or preference. However, I’ve recently learned that I probably wouldn’t be able to pick out the EL84 amp in a blind listening test. I might be able to do that in a blind playing test, but I have doubts about this. My point is that my own personal preference might not have any measurably objective basis. This doesn’t make it any less real for me, but I also don’t want to be insensible about things. When we have more data, more information, we are able to more accurately evaluate what we experience. I guess what I’m saying is that go ahead and feel good about your preferences, but keep an open mind. Realize that these preferences come from a bizarre mixture of experiences, influences from marketing, admiration for other players, and a whole bunch of little biases that all join together to tell you what you think you need.
To further this study into the psychology of guitarists who are approaching ideas related to tube amps, I’ve been combing the interwebs looking for the most common questions and ideas that players have. Here’s what I’ve found
1). We want good tone, especially distorted tone, at reasonable volumes
Power attenuators, master-volume designs, pedals – all of these are certainly solutions to deal with this issue. Personally, I don’t like attenuators. I think they really suck the life out of the sound. Frustration with a 60watt big-name amp plus an attenuator is what got me to investigate building amps in the first place. Master volume designs keep the power section from ever getting saturated, and pedals do the same thing, just in front rather than after the preamp. The big myth here is that wattage and volume are absolutely linked. A difference in 3dB of volume is to be achieved by doubling the output wattage of an amp. In other words, the difference in volume between a 50w and an 100w amp would only be 3dB. It takes an increase of 10dB to achieve a doubling of perceived volume. So, a 40w amp would almost be twice as loud as a 5w amp. There are many other factors at play, including how our hearing is more sensitive in the midrange than it is in the higher or lower ranges. One of the biggest concerns in this discussion is that a lower-wattage amp might get the power section to saturate earlier in it’s volume bandwidth than a higher-wattage amp. It all depends on where you want that break-up point to be. As far as volume is concerned, I have found that the speaker type and configuration matters as much as anything else. If your neighbors are giving you the stinkeye, try a smaller speaker, or fewer speakers, or a speaker with a lower dB rating.
2) We are obsessed with biasing
I wrote another blog post about this issue here. The biggest thing is this: don’t worry! It’s not a big huge deal. If you’re biased too cold, your amp will sound awful. Fix it by heating things up a bit. If you’re biased too hot, you’ll get glowing tubes and they’ll burn up. Fix it by turning it down. It’s can be as complicated as you want it to be, and there are plenty of folks out there who you can pay to do it for you if you’re nervous about getting under the hood. How about this? If your amp sounds and feels good, play it. Biasing always includes a range, anyway. 70% of maximum rated plate current is used as a benchmark, but there is certainly some wiggle room in there.
3) We should know about our components
There are many posts out there on the forums where someone is asking about such and such thingamajoob that is sticking out of their amp chassis. It’s not too hard to figure out what’s what. Basically, you have the tubes, the transformers, and sometimes, a capacitor can. The tubes are the things that look like fancy light bulbs. You’ll have short ones that are preamp tubes (also used as phase inverters and to drive reverb and tremolo circuits) that should have removable metal shields over them. The bigger ones usually come in pairs (unless it’s a single-ended amp like a Fender Champ) and those are your power tubes. Some amps, like The People’s Amp, will have a rectifier tube. There will be only one of these in most cases, and it usually looks much different from the signal tubes. The boxy things are transformers. All amps will have two of them: a power transformer and an output transformer. The power transformer transforms your AC power from the wall outlet into a variety of voltages that the amp can use. The output transformer then converts the signal coming from your power tubes into something that can drive a speaker. There are some more complicated aspects to all of this, but there’s not any voodoo. There might be a smaller transformer or two. Reverb circuits need one, and sometimes something called a choke is used in the power supply of a tube amp. These are small compared to the output transformer, which is smaller than the power transformer. Transformers are some of the most reliable components in your amp, and, unless abused, rarely fail. When you are told not to turn on an amp without being plugged into a speaker, this is to protect your output transformer.
4) We worry about standby switches
We have standby switches for two functions, both of which probably help extend tube lifespan. When we first fire up the amp, we turn the power on, let the heaters come up, then engage the tube by flipping the standby switch. During breaks, we put the amp on standby so that everything stays heated, but the tubes aren’t conducting. Again, the only reason for these things is to extend tube lifespan. The reality is that you don’t need to worry about it. I’d be willing to wager that the wear and tear saved by properly using your standby switch is probably minimal, and that you’re going to wear out your power tubes by playing on them before anything else. Standby switches are cool, they’re fun to use, and they hearken back to the early days of amp manufacturing, when maybe the tubes weren’t as robust or reliable as they are now. They certainly aren’t necessary, and you’re not going to hurt everything if you don’t use them “properly.”
5) We think “Class A” means something it doesn’t
Oh boy. Here we go again. If the engineers who decided how to classify operation had used any other terminology, we’d have been saved from this confusion. We like to get “A’s” on our report cards. USDA Grade A beef is the best. But, when we’re talking about tube amps, Class A just describes a condition under which a power tube is conducting at all times, as opposed to Class AB, in which a power tube might only be conducting as little as 50% of the time. Most tube amps are designed to operate in what is called a “push-pull” configuration in Class AB. That’s why we have power tubes in pairs, and phase inverters. Simply put, each power tube (or half of each power tube compliment if you have 4 of them) will be amplifying half of your signal. They share the work, and your output transformer passes each side along to your speaker. If you only have one power tube (again, think Fender Champ), it’s running in Class A. It’s not a description of quality, but type of operation. Then there is the Vox AC-30 confusion. When Class AB amps are run “hot,” they can behave a little bit like Class A amps in certain regards. Vox marketed the AC30 this way, and people mention it all the time. Here is an excellent article about this. Short story: don’t buy an amp just because it’s Class A, because you think that’s better.
6) We get freaked out when things go wrong
Stuff fails. Especially if you use it. We will always need plumbers and auto mechanics. How often stuff in your amp fails is absolutely dependent on how much and how hard you use it, but a well-built amp like The People’s Amp should be extremely reliable. If stuff goes wrong, here’s a good order to check things:
1) Tubes are the least reliable and most likely components to wear out. That’s why they are in sockets that make them easy to take out and replace. My experience is that at least 80% of problems with tube amps can be related to faulty tubes. Chances are, they’re overdue for replacement anyway.
2) Mechanical components such as pots, switches, and jacks are next. Why? Because they move, stick out, get banged around. Thankfully, they are also easy to change, albeit a little more difficult than tubes.
3) Components dealing with high voltage are the next most likely components to cause problems. Because they are subject to high voltage, and thus, heat. These components include your filter capacitors, the resistors used between them, tube plate resistors, and power tube screen resistors. Sometimes a heater supply will have a virtual center tap added with a pair of resistors that can catch a lot of heat if a power tube shorts. This will add a characteristic 60 or 120 cycle hum. Repairing these sorts of things should be handled by a qualified technician, if you don’t feel confident about doing so.
4) Transformers are very reliable, and rarely fail. Power transformer failures can cause fuse blowing, but if the power transformer isn’t working, nothing works. An output transformer failure can prevent any sound from reaching the speaker, can cause power tubes to short, and can create squealing or motorboat sounds.
The other components in your amp are much less likely to fail, unless they are affected by a failure by one of the components listed above.
What are your ideas about what is important to you? What scares you or makes you worry about your tube amp?
The People's Amplifier 