Tubes Primer, Part 2
Last time around I briefly went over some preamp tube basics regarding configurations and what the numbers on a tube mean. Just to refresh your memory, on a consumer numbered tube (basically what you would have in most amplifiers), the first numbers represent the heater or filament voltage. The next two letters represent the model of the tube (this is really where you find the gain factor of a tube). The number following the letters represents the number of elements inside the tube (meaning how many prongs are sticking out of the tube base). So a 12AX7 is a tube using a 12V heater circuit with an AX gain factor and 7 prongs sticking out of the base. Simple, right?
This month I thought that you might like to have a bit of information that is definitely worth clipping out and keeping close by. This chart is just a small part of the cheat sheet chart I keep for myself. You will also need to have it to follow the gain substitution chart planned for part three of this tubes primer.
You can save yourself a lot of money if you are knowledgeable enough to know the European and military equivalents of your preamp tubes. The numbers in this chart are exact replacements for the consumer numbered tubes in your amplifier.
This table is worth my weight in gold for anybody that may be running low on finances and can’t afford a set of new consumer numbered tubes or even those that want to have a second set of tester tubes around (BTW, a brilliant idea). You may be able to find these equivalent tubes in old electronics laying around your house, or check online for the European and military equivalents. You just might find them a whole lot cheaper.
If you have any questions, you can e-mail me at cs-rocinstruments@sbcglobal.net
Primer of Tubes, Pt. 1
I want to thank those who noticed the Gear Geek column was missing from the August issue, and called me about it. We have my recent hand/wrist surgery to thank for the interruption. It’s that kind of feedback that assures me you are reading Gear Geek.
This month will be the part one of a primer on tubes. If you are like most musicians, you have already decided that there is nothing quite like the sound of a warmed up, slightly overdriven vacuum tube amplifier. But, do you really know the basic characteristics of the tube amp and the tubes? Do you know what the numbers stamped on the side of the tube represent? If you needed to substitute a tube, would you know what you could use?
We know the typical all-tube amplifier is separated into two sections. These would be the Preamp section and the Power Amp section. We will focus in on the preamp.
Typically the preamp circuit tubes are the smaller tubes. You will typically find anywhere from one to three preamp tubes per channel. Each tube contains (2) individual circuits that allow for a variety of configurations. Usually this means (3-4) gain stages per channel and maybe something for spare. Preamp tubes usually use a 12 volt heater, hence the first number stamped on the side, as in 12AX7. In an amplifier with a real spring reverb, you will also find a driver tube. This will usually be the last preamp tube in the series. In most cases, it will also be a 12 volt preamp tube (such as a 12AT7 or 12AY7), but with much less gain than the signal tubes.
Here’s a little field trouble-shooting tip! If you have an amplifier as I described above
(With a driver tube and a spring reverb unit) and think that you are having problems with your preamp section, here is a possible solution. But, first, remember that tube amplifiers hold voltage in the large filter capacitors and it is enough voltage to KILL YOU!
Now, shut off and unplug your amp. If you can identify the tubes by position, normally the driver tube will be the last small tube (V4 in many cases). Pull the driver tube. If you find a 12(XX) 7 number on the driver tube and the other preamp signal tubes (V1-V3) are also 12(XX) 7 tubes, you now have an interchangeable test tube in a pinch. Your amplifier should run just fine without the driver tube installed. Obviously, the best way to go about this is to identify the tubes in advance and have a known good set or at least a test tube with you.
Note: (XX) in the tube number 12(XX) 7 means there could be a variety of letters inserted. The letter variations identify the gain of the tube. For example a 12AX7 has more gain than a 12AT7 or 12AY7.
In the next Gear Geek, I’ll break down all of the preamp tubes in order of gain, the optimum substitutions for each and optimum combinations in typical amplifiers.
If you have any specific questions email Bob at cs-rocinstruments@sbcglobal.net.
“I’m not getting the sound I want out of this instrument, let’s put in new pickups.”
I probably hear that statement and request more than all the others combined. I don’t have any problem taking the business, but I just have this need to educate. Most musicians don’t really know about the dynamics of sound related to their instruments.
There are many things that will change the sound of a guitar or bass without spending more than 20 bucks.
Just installing NEW strings can do it. I am surprised how many times I hear the above statement and find that the strings haven’t been changed in six months. The strings that aren’t breaking are usually the wound strings. The wound strings are also the strings that are collecting the oil and dirt between the winding and killing your sound. Change your strings at least monthly if you are just practicing regularly. That will also allow you to try different styles and gauges.
You might try changing from a nickel-plated string (slightly mellow output) to a stainless steel string (bright output). You might try an iron core (high output) or even a flat wound string (allows for smooth fretting). The gauge of your string sets can change the sound you are getting. The heavier the string gauge you install, the better your tone will be. You will just need to toughen up your paws a bit. Most blues guitarists use heavy gauge strings for this reason. Stevie Ray Vaughn is mentioned routinely and he used a .013 set to get his sound.
Remember, if you are searching for that sound via strings, try changing string material (nickel, stainless, iron, etc.) before changing the string gauge. In most cases, changing string gauge will create additional tension on your neck and it may require an adjustment or full setup.
Another way to change the sound of your instrument is by simply making sure that your pickups are adjusted properly. It is an extremely simple thing to do, but I find that the majority of instruments I see are not even close. All pickups can be globally adjusted in relation to the bottom of the string set. Most humbuckers have at least one set of adjustable pole pieces to allow even more precise adjustments to the individual strings.
Rather than throwing out a bunch of numbers that you won’t remember, just remember this: Shoot for a distance of 3/32″ between the bottom of the strings and the top of the pickup, while you are holding the strings down against the uppermost fret. This is a good place to start. If you want a mellower sound, back off to 5/32″.
After you have the pickups in the ballpark, then you can adjust them for matching output levels. This is simply done by adjusting the global screws up or down one pickup at a time. Some like to leave the bridge pickup a little louder for solos, so it’s your call.
To many of you this may be old hat. It should be. But, I see enough and get asked enough that I know it isn’t. So, before you spend a bunch on magical pickups that will make you sound like Satch, try some of these suggestions. We can look into tonal capacitor changes or wiring mods in future columns if you are interested. Email the editor at <a href=”mailto:charlie@fringemag.com”>charlie@fringemag.com</a> or Bob at <a href=”mailto:cs-rocinstruments@sbcglobal.net”>cs-rocinstruments@sbcglobal.net</a>
It Happens Every Year
Originally, I did not have plans to follow up the February column with more “what you don’t know stuff.” I did want to start giving you real information and knowledge about instruments, stuff that you can do yourself. Then, the after-Christmas crowd started to bring their stuff in. Most of them have NEVER been to a guitar tech of any kind. It happens EVERY year. It was then I realized that I had to get two of these stories to you. You’ll see that you really have to know about your instruments and what to look for.
I also didn’t want you to think that I have a vendetta against Guitar Center or Musician’s Friend or Sam Ash or any other major music retailer. The problem I have is with the consumer not knowing what to look for in a poorly built or ill designed instrument. A guy brought in an acoustic guitar that he had received as a gift in 2006. At the time he didn’t know much about playing, so he didn’t know much about how it should sound. I was asked to give it the once-over. Basically he wanted a setup. He thought the intonation was off and he couldn’t keep it in tune very well (these are things that happen when you actually learn how to play, your ears get better) By the way this was a highly regarded, Far East made, second tier model of a US maker. I did my thing and I couldn’t get it right. So I did it a third time. That’s when I started seeing the problems. Yes PROBLEMS.
More than one. The fret slot was cut on a Friday, manually I guess. There is a mathematical formula used to locate the fret slots. They were in the wrong spots to get the right notes. Normally this is done by a CNC cutter, so they’re perfect. Not this time. On top of that, maybe three or four of the frets toward the headstock were crooked. I was blown away and really did not know how I was going to even explain it. Well, I did and I explained my crusade to at least have instruments checked when you buy them.
Story #2. I believe that this young gentleman was 13 years old. It was his first guitar and he was pumped. This was a Christmas gift. It was from one of the newer FAR FAR East builders that included the guitar, amp and accessories all bearing the same name.. All of the aforementioned dealers carry these for about $150. But it was hard to play.
The action had to be ½” high or more over the 12th fret. He knew to call someone about it. His uncle, who was the gift giver, told him that if he couldn’t play it easily for some reason that it just probably needed to be adjusted. He was right. There’s the argument I get. Why spend $35, even once, to get a new $150 guitar right?
I know a 13-year-old kid that has a screaming little guitar he is happy as hell with and a 30 something gentleman that has a $500+ brand name guitar that he is pissed about because the warranty had run out months before he came to me.
To help everyone out, I’m gutting my Web-site and filling with a lot of my business database. I am rebuilding as I write this, so I hope to have the basic site up when you read this. Originally built to promote my business, ROC Instruments, I now find it is not so necessary. Loyal return business and comments you’ve made on guitar repair sites all over made me believe that I could make the site a little more interesting.
Check it out rocinstruments.com . Keep coming back, I am going to stuff it full of useful information you’ll need to take care of your gear.
Shooting Myself In The Foot
My name is Bob Capretto. I am the owner of ROC Instruments in Vacaville, CA.
I have been building, designing and repairing basses, guitars, amplifiers and effects for nearly 30 years. I am a member of the Association of Stringed Instrument Artisans, also known as A.S.I.A.
I hope to provide both the novice and even the professional musician with a little information to help make your equipment last longer.
Most musicians today don’t have or don’t take the time to find the information that you should know about the instruments and equipment you own. I can’t blame that all on you though. The local guitar shop, where you learned about and purchased your instruments, is basically history. Back when I was a kid, there was a guitar shop in downtown Vacaville called Monk’s Guitar Shop. The guy that owned the place, Gary Miller, was a musician and a fountain of knowledge. He was also probably the nicest and coolest guy I had ever met. He didn’t have a problem with a 15-year-old punk rocker hanging around his extremely small shop and bugging the hell out of him asking questions. He was happy to answer anything I asked and told me that these were things that all instrument owners should know. Monk’s wasn’t there for long. Soon the Mini Mall, as it was known, was no more.
In the ’80s it was the expansion of the big box guitar stores. I remember when there were only six Guitar Centers. In the entire United States. It was during this time foreign builders started hitting the US beaches.
The 90’s brought mail order and the Internet infiltrated the instrument delivery process. The prices got better, but service became non-existent. Young people didn’t know any better and accepted this. I have had instruments come in that have never been adjusted. Many unknowing owners expect their new instruments to be perfect out of the box. All have been shocked when they get a properly setup instrument in their hands. Today there is something missing from the ownership process. All the things that Gary taught me. How a guitar neck reacts to humidity and temperature and why my action sucks and why it needs to be adjusted? Why shouldn’t I move my tube amp right after I shut it down or plug it in right after I have just brought it in from a rainstorm? Why are there so many different string materials and what is the best for me? I can’t do much troubleshooting here, but if you have questions or comments, send them to the editor.
I believe that these are just a few of the many things that any stringed instrument owner should know. There will always be adjustments and repairs that you will undoubtedly have to bring to a guy like me. There are also so many more problems that you can prevent by listening to a guy like me. I could let you make the mistakes and charge you for them, but my conscience says no. Shooting myself in the foot.
