Lessons learned: tube amp repair

Solid state guitar amps are pretty reliable. Tube amps, "not so much" but they produce a better sound.

When you drive a tube amp to distortion, the even-number harmonics are accentuated: the 2nd, 4th, etc. These are pleasing to the ear. But when you drive a transistor to distortion, it's the unpleasant odd-number harmonics that get created.

So tube amps are highly valued by musicians. I had occasion to repair a Peavey Triple-X amp and I have a lot of lessons learned from that. There's not much info on the net so I hope this will help someone, somewhere. I'm sure most of these principles will apply to other amps as well.

1. Whenever working on these, do yourself a favor and replace the driver tube. They're cheap and replacement saves you trouble down the road. This is usually a 12AX7 (a smaller glass tube).
2. When replacing the larger power amp tubes, called finals (usually 6L6GC) never replace just one. Replace them in pairs. In the case of the four-power-tube Peavey, the pattern is ABBA. Replace both A's or both B's as the case may be. If you have a lot of miles on the finals, consider replacing all four, but don't break the pattern if you buy them in matched pairs.
3. Don't put the impedance switch at 16 ohms if you are running into an 8 or 4 ohm load. You're putting the finals under an increased current load.
4. The back-panel fuse is not the only one. This Peavey had four additional fuses inside the chassis. You can only access them by removing the whole chassis from the cabinet. Check them visually or preferably with a volt-ohm meter (VOM). With the switch set to resistance, there should be zero ohms (continuity) between the two ends of the fuses.
   

Enjoy the sweet sound.

Related, dual-purpose scales

One of the things that comes as a "revelation" to new musicians is how closely related two chords can be. For instance, play one bar (four strokes) of a G major chord, open form is fine, followed by one bar of an E minor chord. If you started singing "The roof is on fire", shame on you!

But the purpose of this is to show you how closely related the two chords are. It's almost like the G major makes a statement, and the E minor is a negative retort. Another common example "pair" is C major and A minor; again play them together and you hear the same relationship.

One way in which we put this relationship to good use is that the pentatonic scale for the minor can also be used as a major scale in the related key. Here's a common pentatonic A minor scale in the classic blues/rock "box":

e --------------------5--8--5-----------------------
B --------------5--8--------------------------------
G --------5--7--------------------------------------
D --5--7--------------------------------------------
A --------------------------------------------------
E --------------------------------------------------

This is a great thing to memorize when you want to improvise a Blues or Rock song in A (which by it's nature uses A minor notes.)

But now, play a C major chord before playing essentially the same scale.

e --------------------5--8--------------------------
B --------------5--8--------------------------------
G --------5--7--------------------------------------
D --5--7--------------------------------------------
A --------------------------------------------------
E --------------------------------------------------

The notes take on a whole new, brighter feeling, don't they? You could play a country rock solo with these notes. You've just discovered the not-so-secret relationship between a major and its related minor.

Just for fun, play that last scale backwards, and throw in a response phrase, like so:

e --8--5--------------------------------------------
B --------8--5--------------------------------------
G --------------7--5--------------------------------
D --------------------7--5--------------------------
A --------------------------------------------------
E --------------------------------------------------

e --------------------------------------------------
B -----------6--5--------6--5-----------------------
G --------5--------7--5-----------------------------
D --5--7--------------------------------------------
A --------------------------------------------------
E --------------------------------------------------

Do you recognize the opening to Richard Betts' country-rock classic "Ramblin' Man" by the Allman Brothers?

This box of notes that you play primarily with your index and third fingers will become the best tool in your improvisational bag of tricks.

Exercises?

No, exercises suck! We are guitarists. We want to PLAY things, not engage in boring exercises.

True enough. But you know, when an exercise has helped me as immensely as this one has, I just want to share it with everyone. It's that good. I started this exercise in the late '70's and still do it just about every time I pick up the axe..

The key is getting the fretting hand pinky working in conjunction with the three stronger fingers. At the same time, we use strict up-and-down pattern picking with the right hand to get it stronger and faster, too.

Again, strict up and down picking: even when skipping to the next string, don't break the pattern.

e ------------------------------------------1-2-3-4-
B ----------------------------------1-2-3-4---------
G --------------------------1-2-3-4-----------------
D ------------------1-2-3-4-------------------------
A ----------1-2-3-4---------------------------------
E --1-2-3-4-----------------------------------------


e -3-2-1--------------------------------------------
B -------4-3-2-1------------------------------------
G ---------------4-3-2-1----------------------------
D -----------------------4-3-2-1--------------------
A -------------------------------4-3-2-1------------
E ---------------------------------------4-3-2-1----

Now move the whole thing up a fret and repeat.

e ------------------------------------------2-3-4-5-
B ----------------------------------2-3-4-5---------
G --------------------------2-3-4-5-----------------
D ------------------2-3-4-5-------------------------
A ----------2-3-4-5---------------------------------
E --2-3-4-5-----------------------------------------


e -4-3-2--------------------------------------------
B -------5-4-3-2------------------------------------
G ---------------5-4-3-2----------------------------
D -----------------------5-4-3-2--------------------
A -------------------------------5-4-3-2------------
E ---------------------------------------5-4-3-2----

Do that one all the way up the fretboard.

Now start mixing it up by ascending one fret each string.

e ------------------------------------------6-7-8-9-
B ----------------------------------5-6-7-8---------
G --------------------------4-5-6-7-----------------
D ------------------3-4-5-6-------------------------
A ----------2-3-4-5---------------------------------
E --1-2-3-4-----------------------------------------


e -8-7-6-------------------------------------------------
B ------10-9-8-7-----------------------------------------
G --------------11-10-9-8--------------------------------
D -----------------------12-11-10-9----------------------
A ---------------------------------13-12-11-10-----------
E --------------------------------------------14-13-12-11

These will become second nature after a while. Go slow at first, and strive for accuracy. When you can play the exercises clearly and rhythmically, then and only then go a little faster.

The Magical Plus+ Chord

This is one of those chords that you play in passing but it sounds so good when you slip it in the appropriate place.

The Beatles were classic purveyors of the plus chord. It's what made their songs sound so professional and polished. As you probably know, the Fabs perfected their technique night after night in the seedy clubs of Hamburg. They learned how to play efficiently, which is important when you're playing four shows a night.

Here's a snippet of "From Me to You". This progression corresponds to where John and Paul sing "...keep you satisfied...whoooo, if there's anything...."

      G          G +        C
e ----3----------x----------x-------------
B ----3----------4-(1)------5-------------
G ----4----------4-(1)------5-------------
D ----5----------5-(2)------5-------------
A ----5----------6-(3)------3-------------
E ----3----------x----------x-------------

Note the G+ form is very simple and efficient on the left hand and meshes well with the barre chords.

Here's another example from "Till There was You", written by Meredith Wilson but sung by Paul on the first US album, "Meet the Beatles". It's where Paul sings "...of dawn, and dew, there was love...."

      C 7        C +        F
e ----3----------x----------1-------------
B ----5----------1-(1)------1-------------
G ----3----------1-(1)------2-------------
D ----5----------2-(2)------3-------------
A ----3----------3-(3)------3-------------
E ----x----------x----------1-------------

Ah, a little lower voicing that sounds good played arpeggio, too.

                            F
e --------------------------1-------------
B ----------5----------1----1-------------
G --------3----------1------2-------------
D ------5----------2--------3-------------
A ----3----------3----------3-------------
E --------------------------1-------------

What do I mean by a lower voicing? The plus chord REPEATS every four steps up the fretboard! All these chords are the same, you just slide up the fretboard:

   
e ----------------------------------------
B ----------1----------5----------9-------
G --------1----------5----------9---------
D ------2----------6---------10----------
A ----3----------7---------11------------
E ----------------------------------------

Use the form that sounds best, or the one you can remember easiest.

Nut case

I have a '77 Stratocaster, similar to the one shown in this picture. (pic was borrowed from www.21frets.com/77strat.html)

The problem was that when I restrung using regular light strings, the B string sat too low in the nut. Evidently the nut got gouged a little too far over its lifetime. The slot was so low that the open B buzzed on the first fret.

The solution of course is to change the nut, but if that's not an option, a quick temporary fix is to cut a little piece of the clear plastic sleeve that the strings came in, maybe 1/4" square, and slip it under the string and above the nut. As you tighten the string to playing tension, the string will pop into the slot with the little layer of plastic being just enough to "lift" the string up to where it doesn't buzz.

This "quick, temporary fix" has lasted me about twenty years now!

Soulful, R&B licks in A

Throw these two-note licks in next time you're playing or writing a soulful song. You will even find them in the pop world; bands like Credence made use of these all the time. These examples are in A, but of course with a little work you can transpose them to any key.

Play them as indicated, play an octave higher, just experiment and enjoy the licks that enhance guitar playing and make you sound like a pro.

Note that many of these licks have a hammer-on, which I've indicated with an "h". In case that's an unfamiliar term to you, a hammer is just snapping your ring finger down quickly where indicated, without picking the note. Your finger landing hard behind that fret is what makes it sound out. Remember that during the hammer on, the adjacent string should still be ringing. THAT'S what makes them sound great.


Form 1

e ----------------------------------------
B ----------------------------------------
G -------7--7----7------------------------
D -------7--7h9--7------------------------
A --7h9-----------------------------------
E ----------------------------------------

Form 2 - / means slide up, \ means slide down

e ----------------------------------------
B ----------------------------------------
G ----------------------------------------
D --------7--7-/--9-\-7--7----------------
A --------7--9-/-11-\-9--7----------------
E ---7h9----------------------------------

Form 3

e ----------------------------------------
B ----------------------------------------
G -14----14-------------------------------
D -14h16-14--14----14---------------------
A -----------14h16-14--12-----------------
E ----------------------------------------

Form 4 - While barring the two 5th fret notes with your index finger, pull (bend) them both down slightly.

e ----------------------------------------
B ---8--7--5(b)---------------------------
G ---9--7--5(b)---------------------------
D ---------------7------------------------
A ----------------------------------------
E ----------------------------------------

Form 5

e ----------------------------------------
B ----------------------------------------
G ----------------------------------------
D ----------------------------------------
A ---5--5---5--7----7---------------------
E ---5--5h7-5--7h9--7---------------------

Gettin' in tune with Zeppelin

How do you tune your guitar? These days it's nice to have these digital tuners, built in to your amp sometimes. Tuning couldn't be easier.

But once upon a time there were not such nice options. You could get a pitch pipe or harmonica, and if you knew what key it was in, you would tune until the fretted chord (in A major, let's say) sounded the same as blowing into your A harmonica. Crude, but it worked.

Back when it was just me and "blondie" (my 1976 Fender Strat), I had a little routine for tuning up whenever I changed strings. I would put on side one of Led Zeppelin, the first, eponymous album by Messrs. Page, Plant, Jones and Bonham.

The songs on side one were perfectly in pitch on a standard turntable. I could tune up to the songs on side one, and well before I got to the last track, "Dazed and Confused", I was spot-on and ready to rock.

Here are the songs on Side One and the key they're in:

"Good Times, Bad Times", in E major. The chorus, where they sing the title, is in A major. The break "Sixteen, I fell in love..." is in F# minor.

"Babe, I'm Gonna Leave You", A minor.

"You Shook Me", E major. A fantastic blues; try to follow Plant's voice with your guitar by playing the pentatonic scale on the twelfth fret! Let me get you started:

e ------------------------------
B ------------------------------
G ----------12------------------
D ----12-14----14-12-14---------
A -14---------------------------
E ------------------------------

Finally "Dazed and Confused" continues in E. Check your high strings' tuning by playing along with the opening harmonics:

e ------12(h)-----------5(h)----
B -12(h)------------5(h)--------
G ------------------------------
D ------------------------------
A ------------------------------
E ------------------------------

PS: Just in case you're new to playing harmonics, here's what you do:

1. Touch the index finger of your fretting hand lightly on the high E string, directly over the twelfth fret. Just hold it there, lightly.
2. Pick the high E string with your picking hand, and immediately pull off your fretting index finger.
3. You should hear the string ringing like a bell.
4. Practice the other rich harmonics: over the fifth fret, the seventh fret, and the ninth fret. They are all marked with dots or bars on your fretboard.
5. Practice harmonics on the same frets on the five other strings, too.
   

A great album, enjoy it while you're tuning up. Play the rest of the LP (CD) too!