The Mildly Interesting Vox AC30 Reverb Problem

Mark’s like-new Vox AC30 worked well, except nothing came through the reverb signal path.  The foot switch checked out, so we loaded it up and worked on it at the Unbroken String lab.


A gorgeous amp, built like a tank, sounds sweet, but no reverb.  Slapping the tank didn’t bring forth any spring sound, so it’s time to get it on the bench for some minor surgery and some amp tech porn pics!

This amp was purchased new just a few months ago from a major retail chain.  Even a Chinese amp should be pretty solid for a few months.  Now I’m really curious what is going on here.

10 LoudspeakerSome amp tech porn.  Wharfedale supplied loudspeakers for AC30s for one year, Sure enough, here they are!

The chassis slides out of the back of the amplifier.  Time to check the preamp tubes, seen mounted horizontally behind the final amp tubes in the foreground.

Well, that was easy to find.  The current through this tube barely moved the needle.

06 OverheatedComparing the bad tube to its neighbor, the getter material is a little darker.  Nothing else out of the ordinary here.

07 SovTek GoodnessThankfully, economic sanctions against the Russians haven’t pinched off the free flow of SovTek 12AX7 tubes. Yet.

08 New TubeSome techs cuss at the rubber shock mounts around the tubes as you see here because they interfere with inserting the tube into the socket.  But the tube gods smiled this afternoon.

09 First TestWe are ON but nothing is coming through the reverb circuit.  Again.  Uh oh.  Have I failed?

11 EMI Choke1A visual check sometimes yields the quickest results.  Nothing was out of the ordinary.  But this clamp-on ferrite choke does not appear on the schematic.  The red and white RCA cables go to and from the reverb tank.  What’s going on here?

13 Bottom ConnectionsThe other end of those red and white cables terminate in the bottom panel of the amplifier cabinet. The cables from the reverb tank plug in here.  The signal passes through the amplifier cabinet through these bulkhead RCA connectors.  Interestingly, the loudspeaker wiring goes through this quarter-inch jack, greatly simplifying service. Thank You VOX!

12 Broken WireThis is a view from the other side of the black panel in the previous picture.  This open white wire goes to the RCA plugs that actually plug into the amplifier circuit.  Now we’re onto something!

14 Test Run1Space is cramped, so I took some time to set up this portion of today’s program.  I removed some solder from the RCA bulkhead connector, so I can make a new solder joint.  I’m using a pair of tweezers to get the wire lined up because my big fat fingers won’t go inside the amp here.  And I don’t want to be anywhere near the hot soldering iron when I’m fixing this.

15 FixedAh, that’s much better.  The original Chinese solder was that high-melting-point lead-free stuff, containing lots of tin.  In my experience, the lead-free solder is a bit brittle, so this particular solder joint was at-risk since the day it came from the factory.

16 Strain ReliefWhile I’m on a rant about lead-free solder, let me rant about this ferrite choke.  This part has nothing to do with sound reproduction or tone, but was likely added in an effort to comply with FCC or UL regulations.  The only support for this choke was the wires from which it was dangling, and you saw the damage it caused.  Here, I’m using a tie strap to hold the ferrite choke away from anything delicate.

17 Outta My WayWhile I’m at it, I’ll add a second tie strap.  That should keep this from happening again.

18 HookupNow everything is hooked up again and the reverb tank really, well, reverbs!  I think we’ve got it fixed now.  This is a nice shot of how the signal path moves from one section of the amp enclosure to another.

19 Chassis ScrewsI had forgotten how many screws had been removed to take this guy apart.

20 ReassemblyHere’s more screws.  Are we there yet?

21 Final TestMark has his amp back and he is pleased!  He mentioned that this amp is for sale, so if you are interested in this unit, drop me a message from the “Contact” page and I’ll hook you up.


Thanks for reading all the way to the bottom!


David Latchaw

Cell : 281-636-8626

Major Fender Mexican Stratocaster Rework

This lovely all-black (murdered) Mexican Strat is another one of Dr. Shoen’s axes.


This guitar had languished in the trunk of a car and had acquired an interesting twist in the neck.  A very fine white dust permeated every internal cavity of the guitar.  The tremolo was functional but for some reason, releasing the tremolo did not necessarily return the tuning of the open strings to where one would expect it to be.  A few of the bridge adjustment set screws were corroded beyond usefulness.


A conventional setup was just not adequate to return this guitar to playability.  More work was needed.  This is something that happens from time to time… a situation that every guitar tech dreads. However, I run where angels fear to tread!


Let’s press onward to disassemble this guitar, do a little exploratory surgery, and take some guitar tech porn pictures along the way!




02 HeadstockBadgeHere’s all the info you need to make illegal copies of this guitar, complete with a valid serial number.

03 StringsThese are Dr. Shoen’s preferred string set.  When I asked him why he puts these strings, he said that they are the cheapest.  Excuse me while I scratch my head.

04 OriginalTremStringsCan you see the fine white dust in the left end of the tremolo spring cavity?  Another OCD peeve of mine is tremolo springs installed this way.  Somehow it makes sense to some people, but the center spring will go slack before the outside springs.  For a constant spring rate, the springs need to be parallel.

07 TremStringsOffOff they come.  I feel better already!

05 LockingTunersGuitar Tech Porn.  Nice locking tuners on the headstock of this Strat.

06 NeckOffOff comes the neck.  No shims?  The geometry of this guitar will change as we rework the neck twist and retrofit the bridge with new set screws, so I’ll go with this configuration and add shims later if we need it.

08 BridgeOffThese screws are really loose, almost falling-out loose, particularly on the treble side.  Perhaps this has something to do with the tremolo not returning to an in-tune condition.

09 DirtyNeckThis fretboard was cleaned and oiled in the first setup.  The guitar had not been played much since then.  I suspect that the oil has floated out some more grime from the pores of the rosewood.

10 DirtyNutSome grime was softened around the nut, so I will apply this super-secret cleaning tool to the nut.

11 HeadstockAlignmentGuitar Tech Porn.  Lockers are unlocked, string holes are lined up, and there is a slight reflection of the nut in the surface of the rosewood fret board.  Nice, wouldn’t you say?

12 NewBridgeSetscrewsI began to disassemble the bridge and prepare to install new set screws.

14 InstallNewBridgeSetscrewsThe new set screws are wrapped in Teflon tape, then threaded in from the bottom, where the Teflon will gently lock the screw in place while permitting adjustments in the future.

13 OriginalBridgeCleanedUpThe bridge is ready to return to service.  Those tiny scratches are from the ends of the old set screws.

16 ReassembleBridge2Guitar Tech Porn.  This is a side view from the low E string side, showing everything going back together.

15 ReassembleBridge1Guitar Tech Porn.  Another view of the new set screws.

17 ReassembleBridge3The bridge has been reassembled.  Before the strings are installed, I’ll tighten the intonation screws so that the saddles slide forward onto the open string as the intonation is set.  I’ve discovered that if I start with the intonation screws fully extended, as they are here, tightening the screws results in string deformation as it rides over the saddle, and takes forever for the string to settle back into a ‘straight line.’  While the string is straightening out, there is no point in doing any further adjustments.  Waste of time.  So now I ‘subtract’ unsupported string length by moving the saddle forward to set intonation.  The vibrating portion of the string is always ‘clean.’  Or I’m just OCD.  Again.18 ReinstallNeckThe neck goes back on without a shim, so we can see where we are with the other adjustments.

20 InstallNewStringsGuitar Tech Porn.  Slip the strings into the locks and tighten them down.  Love it!

19 ReinstallBridgeThe saddle should ride flat on the guitar body.  It takes a while to get the screw heads in just the right place for this saddle to stay put.  I’m a little worried that it won’t stay put when the string tension takes over.  We shall see!

21 ReinstallTremSpringsThis is the way an OCD Guitar Tech installs tremolo springs.  It is also OK to put the two springs on the outside and have one in the middle.  For now, this will work OK.  I’m also thinking that those screws holding the bridge in place aren’t going to stay put, so this just seemed like the safest thing to do.

22 JenTest1Jen works the Strat into a lather.  Sure enough, the tremolo is acting up again and the low E string is buzzing.  Again.

23 JenTest2The tuning pedal shows that the tuning continues to change as she plays the guitar.  Not good!

24 NewBridge1Time to pull out the big guns.  Callaham Guitars has a premium tremolo assembly for Mexican Strats.  There are a couple of key differences that will help this guitar out, as we will see below.  The strings and neck come off the guitar again at this point.

25 NewBridge2A thing of beauty, the Callaham bridge is visually very close to the original Fender part, except for the CG stamp on the saddles.  Referring to the earlier picture of the intonation screws, here I’ve got the saddles pulled all the way to the back so that the springs are compressed.  As intonation is set, the vibrating portion of the string will get shorter.

27 BridgeComparison1Here’s the real difference.  On the left is the original Fender bridge, and on the right is the Callaham bridge.  Note that the bevel does not extend all the way underneath the screws.  This should allow the screws to be tensioned adequately to hold the bridge plate down, yet allow the tremolo to pivot the whole assembly on a single axis.  In other words, the axis of rotation of the bridge assembly is held in a more stable point, right at the ridge of the steel, right underneath the screws.  In the Fender system, we lose control of the geometry of the bridge once the bridge plate tilts, as there is no groove or knife edge anywhere on the screws to act as a specific pivot point.

26 BridgeScrewHolesStripped1Another big issue with bridge stability is that the screw holes on the treble-side strings are stripped.  The wood used to make this guitar body is a little softer than I expected, maybe alder.  (You Strat-heads can message me with your inputs on this subject.)  My plan is to cut plugs from rock maple, drill these six holes to fit the hardwood plugs, then re-drill the hardwood plugs to fit the Callaham bridge.  I’m not a big Tone Freak but I have a feeling that the “Q” or the mechanical resonance of the body will be a little higher with the bridge screws held in place with rock maple.  Maybe Les Paul was on to something when he laminated maple over mahogany.

30 GluePlug1The plugs were cut using the 3/16th plug cutter from Stewart-McDonald.  This 3/16th inch plug cutter makes the smallest practical sized plug available, to my knowledge.  The smallest plug cutter I could find otherwise made a plug that was 6mm in diameter.  Here is one of the rock maple plugs getting a coat of hot hide glue.  The plugs are a little longer than the holes in the body, so I have something to hold on to!

31 GlueHole1The inside of each hole gets a coat of hot hide glue, too.  It takes about a minute to get each plug into the body of the guitar, at which point the hide glue begins to harden.

32 TrimPlug1Each plug is carefully trimmed flush with the original body contour.  This takes a while.

33 CenterMarkPlug1The new Callaham bridge is positioned at the point where the intonation adjustment will do the most good, then is held in place with some No-Mar tape.  A brad-pointed drill bit is used to mark the center of each screw hole.

34 PrepForDrill1This body is just wide enough to prevent me from using the drill press.  Everything is taped off so I can use the hand-held Port-A-Lign to drill the screw holes accurately.

35 Drill1The Port-A-Lign is doing its magic.  The rock maple plugs go all the way through the body, but the screw hole depth is limited to the exact screw length by controlling the length of drill bit extending beyond the jaws of the Jacobs chuck.  This allows the longest possible contact between the screw and the rock maple, all the way to the tip of the screw.  A tiny bit of tape covers the ends of the chuck jaws, in case I hit the rock maple with the Jacobs chuck.

37 NewBridgeInstall1Guitar Tech porn.  The Callaham bridge kit even contained new screws.

29 TinTremClawThe Callaham tremolo spring claw was not tinned to accept a ground wire.  No problem.  I have a big soldering iron.  The claw rests on a piece of ceramic tile because it gets WAY too hot to sit anywhere else while I’m doing this.

28 TremArmComparison1The new Callaham tremolo arm is at the top, and the original Fender arm is on the bottom.  Dr. Shoen prefers the longer arm.  They are mechanically interchangeable, in any case.

38 FinallyFinishedI got ‘medieval’ with the neck to get the twist out of it.  No pictures, because it wasn’t pretty, and both my hands were busy.

After the strings were re-installed and the setup begun, I really didn’t need any shims in the neck.  String buzzing was gone.  The new bridge made it easy to radius the strings and set string height.  Intonation was dead-on for where I placed the new bridge, with little adjustment necessary.  Four tremolo springs were installed to get the tremolo working perfectly. I picked up this guitar to play it and didn’t put it down for forty-five minutes.  It was alive in my arms.  And I hadn’t plugged it into an amplifier yet.  The sustain of each string was fantastic.

Dr. Shoen played it acoustically, with a lost look on his face.  I was afraid something wasn’t right.

When he looked up, he said that he was ‘inspired’ by playing this guitar.  He felt that I took a $500 guitar and turned it into a $1000 guitar.  Jacked into my Gibson amp, this thing just sang.

Now go out and get that guitar out of the trunk of your car,


Thanks for reading all the way to the bottom!

CONTACT INFORMATION – David Latchaw  281-636-8626


Epiphone Les Paul LP-100 Checkout

EPI01 Another Stolen GuitarJennifer found this stunning Epiphone Les Paul at a local music store.  They didn’t know what they had!  Let’s clean it up.

EPI02 DestringThe only issues I can see are that the pick guard is white but the other parts are ivory.  The nut is probably polycarbonate.  All the other hardware and pieces appear to be pretty good stuff!  Off come the strings.
EPI03 Headstock Is A MessOne of my pet peeves is long, dangly string ends.  Why can’t people watch a few YouTube videos and make their guitars a little less dangerous?
EPI04 Hardware1The tail piece is branded Epiphone and is steel.The bridge is steel as well, also branded Epiphone.  String saddles are steel.  Everything here is in good shape.Jen wanted to remove the pick guard.  It didn’t match, and she likes the Studio ethos of a Les Paul sans pick guard.I have been told that this is called a pickguardodectomy.  From this view, you can see the mismatch of colors.My guess is, this guitar has never been polished since it left the factory. The finish is otherwise in great shape!The knobs were not cracked and were not stuck on the pot shafts. The nuts were tight.The neck pickup had been screwed way down, but was functional at the music store.  Here, I’m temporarily removing it so we can clean up everything.The saddle studs were very loose in their holes, so I bushed up both of them with half-inch Teflon tape.I checked the electronics.  Everything was functional at the music store. I removed the covers to remove gunk and better polish the finish.  This switch is 100%.The jack is like-new. Again, I removed the cover to better polish the finish. Note the more-than-adequate service loop. I wish more guitar companies did this, but, alas, copper wire costs money. Thus, you can always be assured that you won’t get any more than necessary. But this Epiphone is a welcome change from the norm.The bushings on the top side of the tuners were not even finger tight. I’ll take this opportunity to pull off the hardware and polish the headstock.The entire neck is finished. Here are some cryptic marks on masking tape for you to decipher.True to the Les Paul formula, this body appears to be mahogany with a maple top.After I installed the neck, I noticed that the badge on the headstock appears to be an inlay, perhaps synthetic abalone.The front of the body is done and is ready for strings. The neck got the usual fret polish and cleaning. The fret board was filthy, taking three applications of Dr. Duck’s to bring it back to life.The back is absolutely perfect, no buckle rash or any signs of chips or damage.Strung, tuned, truss-rodded, string-heighted, intonated, played.  Jen found a real winner here!Welcome to the Les Paul Zone!