Gibson C-0 Classical Guitar Fret Dress

An interesting tool came in the mail from the good folks at Grizzly Tools. This file is polished smooth, with two quarter-round concave file surfaces on opposing corners. It can be used as an alternative to the traditional fret dressing file. Let’s try it out on my 1968 Gibson C-0 classical guitar, that was cleaned up in an earlier post but could still benefit from a thorough fret dressing.  (Photo courtesy of Stewart McDonald.)

I’ve recently added a leather sandbag to my luthiere tool set. The little bunny ears really hold the neck securely. NOTE: Be Aware that this bag is sold as a rest for use at the gun range, but makes an awesome neck support.

The mat is a section of a floor covering used in gyms.  These mats are often used underneath workout machines and in the free weight areas.  They are tough and plenty cushy, just the thing for your luthier’s workbench.  And one mat can be slit into enough pieces to outfit four or five guitar workstations.

I covered the sound board with a sheet of corrugated cardboard. No sense in risking any damage to that fifty-year-old piece of cedar!  A pair of heavy-duty scissors is barely adequate for the job.

So here’s the cardboard sound board cover at work.  This will keep stuff out of the sound hole as well as help prevent gouging the guitar.

The frets are leveled with emery paper glued to this straight edge.

Here we are going to work with the new file. The file works best with the wide part of the blade vertical to the fret board when going along the length of the fret wire.  You can see a little black magic marker on the tops of each fret wire, which serves as a visual indicator on where (and where not) to remove material.

With this file, I did not feel it was necessary to tape off the fret board because the filed particles were not small enough to lodge in the grain of the rosewood. Also, the thickness of a layer of tape would have held the blade of the file away from the corners of the fret wire ends that needed to be dressed. The fret wires were very smooth after the filing was complete, so the fret polishing was almost trivial.

The creation of this saddle was documented in an earlier post. We’re ready to restring!

I can say that these strings are excellent! They are just a tiny bit smaller in diameter than the Augustine strings I had been using, and no intonation problems. These are a keeper!

Some customers wanted more pictures of how I tie off the classical guitar strings at the bridge tie block. Note that the ends of each string is tied underneath the loop of the string next to it.  I start at string one (high E) and then secure the end in the loop of the next lower string.  This looks neat and really assures me that the knot will not come loose and the string come untied.

Here, I’m taking my time to show how the last string (string six or low E) is tied off.  The direction of the wrap forming the loop is in the opposite direction of the wrap used on the higher strings.  This causes the free end of the E string to ‘point’ in the direction of the A string, in whose loop it shall be secured.

Now the knots in both strings are pulled tight. You can now see how the A string really holds everything in place.  The end of the A string projects through the loop of string six (the low E.)  We’re done here.

As I work on this guitar more and more, it gets better and better. These new strings sound wonderful. Leveling and dressing the frets make every note crisp and clean all the way up and down the fret board. The Grizzly fret file is a keeper!

Thanks for reading all the way to the end!


CONTACT: David Latchaw EE


Fender Bassman LTD Tweed Factory Workmanship Problems

This beautiful reproduction amp worked well for a while, then began to exhibit strange symptoms. After quitting entirely, the owner called the Unbrokenstring Crew.   Can we fix it?  Yes we can!

At first glance, this amp looks to be a chip off the old block. Other than the label on the back and the like-new condition, this amp is almost indistinguishable from the original model.

The lovely control panel lends a little mirror-like bling to the case.

WARNING: Tech porn. My, aren’t we starting early in the post with the porn?

The chrome faceplate shows every fingerprint.  This will need to be polished before the owner gets his amp back.

The silkscreen is a little worn off the nameplate but the chassis model is intact.

You can clearly tell that the cabinet is pine and not plywood nor MDF board.

WARNING – More Tech Porn – If you turn up the sound, you can hear some heavy breathing! Let’s fix this!

The rear panel is lined with aluminum tape.  The green wire grounds the foil to the rest of the chassis.

Here we see the hand-wired tube sockets.  Although I would like to have seen the control panel hand wired as well, this is overall the best way to build a tube amp, IMHO.  The dangling green wire is the ground wire to the foil seen in the previous picture.

The chassis wiring is a combination of wire-to-board and wire to flag terminals.  Two printed circuit boards are employed; one for the components in the amplifier itself and another one for the front panel control wiring.  Also note that the loudspeakers say “SPECIAL DESIGN.”  I’ll explain what that means later.

Here we see the input jacks and preamp tubes.  Sorry about the glare in the pics.

Let’s get that circuit board out, because I found a bad connection that requires solder rework.  The input jacks are already loose in this picture.

The nuts on the controls are called ‘small outline’ which is a nice touch that Fender added.  The small outline nuts will not show when the chicken-head knobs are installed.  Off they come!

Some sound came out of the loudspeaker when tapping around this area. What do you think we will find?

The stripped part of this wire may have been soldered at one time, but the solder joint failed. This wire pulled right out with nary a tug.

This grey wire also came out.  We need to remove this circuit board in order to do some serious work on the solder side.

There are about twenty five flag terminals with wires on them that need to be removed in order to pull the circuit board out of the chassis. Each wire is marked with nomenclature that matches the identification information on the circuit board silkscreen. Here, I’m making numbers with my Brother label machine.

Each number was repeated so that the label could be read from either direction. Here, the label is formed into a flag and looped around the wire.

As I moved the wiring around to free the circuit boards, more wires came loose. I speculate that the lead-free soldering was performed at the wrong temperature or with a flux that did not allow the strands of the wires to be adequately tinned while the joint was formed. Over time, these failed.

Each failed solder joint was re-flowed with real tin/lead solder using activated rosin flux. This rosin flux is not conductive, but the dust it attracts is conductive. Rather than take a chance with future problems (and to keep my workmanship looking nice) the circuit board is manually de-fluxed.

There. That’s better. This is what the solder-side of this board should have looked like when it left the factory.

And now it’s time to put this amp back together. This is where all those wire flag markers come in handy.

Yes, REALLY handy.  There are a lot of connections to be restored and I would have had some issues had I not marked each one with a flag.

The amp is back up and running. Here’s a pic of the bias check. Can you see how many milliamps flows through the tube pair at idle?

Here’s a pic of our favorite green wire, seen in an earlier photograph!

One of the screws would not tighten, so here you can see that I’m blowing out the debris from the hole prior to plugging it and drilling the plug to hold the cabinet screw securely.

All done. Do you remember that I mentioned something about those ‘Special Design’ loudspeakers? Well, if you ever want to replace these loudspeakers with other units, Be Aware that the magnets on those new speakers will hit the amplifier chassis. Be very careful to replace these loudspeakers with ones that will mechanically fit. Just sayin…

Thanks for reading all the way to the bottom!

CONTACT : David Latchaw EE