Yamaha G240 Classical Guitar Refurb

Donny mentioned that this beautiful 1970s era Yamaha needed a set of strings.  Turns out, it could use a little TLC.  The Unbrokenstring Crew steps up to the plate to bring this classical guitar up to speed!

 

Intended as a student guitar, these wonderful old Yamaha guitars rival many medium priced guitars found today.

 

The serial number is hand-stamped on a soundboard brace.

 

At the time, we considered Made In Taiwan as junk.  Nowadays, that was the Good Stuff!  How times change…

 

Obviously the nut is unglued, but note that the rosewood fingerboard had been painted black, to give the appearance of ebony.  Such was the snobbery found in the classical guitar world back in the 1970’s.  My first classical guitar sported a black painted fingerboard, and it looked a lot like this after years of playing.  Nothing to be ashamed of nowadays.  In another fifty years, we’ll be playing guitars with synthetic Richlite fingerboards, and consider rosewood fingerboards as ‘high end’ and collectible.

 

This diamond file is removing the old glue and truing up the gluing surface on the neck.

 

The diamond file is working on the end grain of the fingerboard.  That little cavity under the nut is not for a truss rod, but rather appears to be a slot for a stiffener of some sort.  Classical guitars seldom use truss rods to counteract string tension, as nylon string tension is about a third of the tension created by steel strings.

 

Any glue remaining on the nut itself comes off using the mill file.

 

Some alcohol on a rag cleans off residue on the nut.

 

Time to clear out the old DNA and tune up the string slots in the nut.

 

This is a serrated wire used to clean orifices on cutting torch tips.  They are often re-sold for many times the price by companies servicing the luthier craft.  Just get yours from the car parts store or a good tool store.

 

The tip cleaners come in many sizes, so just use a micrometer to select the correct size for your application.  Here, I’ve moved to the B string.  The rest of the slots are clean and smooth, so I’m done here once this slot is smooth.

 

Looks good!  We’re ready for some hide glue.  But how do I clamp it down?

 

How about using a couple of the old strings, brought up to tension, to keep the nut in place for a day or so?

 

This guitar was missing the saddle.  Here, I’m shaping a piece of Vietnamese water buffalo bone on the belt sander.

 

The water buffalo bone is incredibly hard, a natural material, and a renewable resource as opposed to ivory.  Some of the new synthetics are good, but I have this in stock and I love grossing out the other Unbrokenstring Crew members.  Bone? Dead animals?  Yuck!

 

The Yamaha saddle is about 0.100 inch thick.  These blanks are about 0.140 inch thick to start.  After a few minutes, I’m down to 0.137 inch.

 

We are at 0.131 inch.

 

Down to 0.121 inch.

 

Can you read this one?  0.115 inch.

 

Almost there!  We’re at 0.103 inch thick.

 

As George Bush would say, we have destinated!

 

The trial-fit part of our program is complete.  Note that the saddle is a little long.  There is a method in my madness here.  Let me introduce you to a real luthier who can explain what I’m trying to accomplishing here:

Q: Why do the British like Lucas refrigerators?

A: Because they like warm beer.

Seriously, the last thing I want to use on a fine musical instrument is lubricant that oxidizes and turns into gum.  Synthetic lubricants don’t oxidize, and so make a better choice when metal-to-metal lubrication is needed.  Such as in tuning machines.  This Lucas product is thick enough to stay in place when assembling engines.  This lubricant will stay in place on a musical instrument.

 

I need to install some strings in order to set the action at the twelfth fret.  Before I do much more with these tuning machines, I will lubricate them and set the gear mesh so that the guitar will stay in tune yet the tuners will run smoothly.

 

I re-used a couple of the old strings to accomplish the string height setup.  One of them has a ball end!

 

Stupid Me.  The old strings were worn and did not have a constant cross section.  Thus, I got weird, inconsistent readings.  I’ll use a new string.

 

Same with the high E string.  A new string is pressed into service in order to complete the setup.

 

The top edge of the saddle will be rounded off in order to remove any sharp edges that may cut the strings.  A rounded top edge also allows a single point to support the string, resulting in better sustain.

 

Now that we have the saddle to the proper dimensions, every surface will be polished with a high speed buffer.

 

The bottom edge of the saddle blank gets special attention.  Here the blank is set level with the jaws of the vise.  The jaws will act as a guide to keep everything straight and true.  A polished, flat surface against the bridge will permit the best transfer of energy from the strings to the soundboard.  The variation in color in this piece of bone is due to the changes in orientation of the grain of the calcium in the bone.  This gives an almost opalescent appearance to the saddle.

 

The top of the blank is polished, yielding a hard surface to support the strings.  Note that this end of the blank is curved.  This marks the orientation of the saddle; the rounded end points in the direction of string 1 (high E.)

 

The faces of the saddle are polished as well, mainly for appearance.  Note again the presence of the calcium grain.

 

Time to string it up.  Here you can see the wedge shape of the saddle, which allows the user to set the action height.

 

All laced up!  The free end of the adjacent string is secured in the loop of the next string over.  I’ve never had to retie a string or tie an additional knot when tying the string ends off in this manner.

 

She plays beautifully and the intonation is perfect!

Thanks for reading all the way to the end!

David Latchaw  EE

281-636-8626

Fender Princeton 112Plus Jacked-up Input Jacks

Worn input jacks are the bane of players and the bread and butter of amp technicians everywhere.  The Unbrokenstring Crew is ready to Slay the Bane and get this wonderful unit back on the air!

 

Most commercial equipment manufacturers sell their gear world-wide.  The European Union (and other areas of the world) have stringent requirements regarding electrical isolation of the consumer and any electrical parts of the equipment, including the grounded chassis.  Thus, synthetic insulative materials are pressed into service for input jacks, although the longevity of that material is nowhere near the longevity of steel.  Such is the world we live in.

 

We’re taking a quick tour of the rest of the front panel.

 

These jacks aren’t in much better condition.  The synthetic material just degrades over time.

 

We’re documenting some connections here, so that we can disconnect them to remove the amplifier and then get them properly connected during reassembly.  The reverb tank lives in the bottom of the amplifier cabinet.

 

More documentation, and a little Tech Porn!  Loudspeaker connections are shown here.

 

The circuit board is typical of Fender gear from this era.

 

These screws hold the output module to the heat sink and thence to the aluminum cabinet of the amplifier.

 

Oops, I did it again!  A little tech porn, this time the high voltage fuse which protects the high voltage transformer.

 

I believe that this is the date when this amp was built.

 

With the circuit board free from the chassis, we have our objective in sight!

 

Here is a quick view of the other front panel jacks.

 

Here are our new jacks.  Next, all the nuts holding the controls will be reinstalled.  I have spared you the details of replacing the jacks and the soldering and all that.  If you want to see that process up close and personal, check out the Gallien-Kreuger jack repair in an earlier blog posting.

Here’s Jacob doing a checkout:

 

This unit is 100% electrically.  New knobs are on order, but I’ve returned this amp to the owner as-is.  Later, I made a trip to his place to install the knobs and audition the amp.  As it turns out, he is quite the Jazz Cat and is really enjoying this amp.

Thanks for checking out my blog post!

David Latchaw EE

281-636-8626

Moss Custom Amp Head Surgery

What have we here?  A road case for The Deer Hunter?  Or perhaps a Big Buck Body Bag?  Let’s See!

Zach says his amp plays like crazy but one tube will red-plate.  The high voltage place power supply fuse will blow.  This cannot continue.  Can the Unbrokenstring Crew help?

Awesome dinosaur visuals dominate the Plexiglas window, and the Tolex deserves a closer look. Wow!

Five preamp tubes handle preamp duties on two input channels, driving two pairs of 6L6 tubes that can be split for half-power operation. No rectifier tube in sight, so I assume solid state rectifiers live under the chassis. I really like the beefy switches used for selecting the input voltage and setting the loudspeaker impedance.

This Tolex covering makes me drool like a noob. Just stare at it for a while. I am already dreaming up future projects that I will start just so I can cover them with this stuff. Yes, I know where to buy it in quantity.

This light show drew a lot of attention around the office. The Plexiglas is etched on the back side. Red LED light shines invisibly through the clear Plexiglas but scatters toward the observer’s eye when it hits the etched pattern. A small green LED makes a feeble attempt to illuminate the tubes. Extra Credit For You if you can see it.

A confirmed NO AUDIO condition launches some exploratory surgery. Based on the red plate report, we should look around inside before burning up any more tubes. This unit uses commercially-available parts throughout; the sticker for the output transformer lives on the chassis near the transformer itself.

Along the same lines, AC power conversion is handled by this off-the-shelf transformer. I really like how Moss has done this ‘build.’

A fresh fuse of the proper ratings now lives in this fuse holder. If you ever do this yourself, BE AWARE that voltages and currents at this point are LETHAL, even with the power cord unplugged.   This fuse is not considered a user-serviceable component for this reason.

The high voltage rectifiers and filters are on the upper eyelet board.  Low voltage DC is rectified so that the preamp tube filaments are always fed direct current.  A 5v power source for LEDs and control switching is found on the lower eyelet board.

The circuitry for the preamp tubes are to be found on the lower center eyelet board.  If I had done this amp, I don’t know that I would have done a thing differently!  Well done, Mr. Gelinas!

Can you say that you have made something that you were proud to sign you name to it?

We’re up and running with a set of shop spares fulfilling the role of output tubes.  During the second day’s test run, power consumption increased slightly, then things started happening quickly.  I shut the amp off as the third tube from the left began to get hotter than usual.  I did some circuit checks, then restarted the test.  Later, the same thing happened again.  I moved tubes, no difference.  But the problem didn’t happen every time.  Turns out, I had a parasitic oscillation that occurred only in tube 3.  Sorry, no oscilloscope pics, but they come later.

Parasitic oscillations may occur whenever energy storage components (capacitors, inductors) are used in gain circuits.  Parasitic oscillations are rare in audio circuitry, but can happen.  The inductor hidden in this picture is in the form of the wire wound cathode bias resistors, seen here as those white rectangular items in this picture.  These happen to be made by Xicon, the inexpensive Chinese house brand carried by Mouser Electronics.

The white Xicon resistors have been removed and replaced with these non-inductive wire wound resistors of the same resistive value and wattage.

These resistors also came from Mouser, and just cost a few cents more than the Xicons that are now in the bottom of my trash can.

Now that I have some confidence that we have a handle on the root cause, we’re installing a fresh set of JJ Tesla 6L6 which is what Moss used when they built these amps.  And I have a local dealer.

This is my favorite part of the job!  It’s beginning to feel a lot like Rock and Roll Time.

This is what 100 watts into a non-inductive eight ohm solid state load looks like with a 440 Hz (concert A) sine wave running through the clean channel into four paired push-pull 6L6 tubes.  No fans were used to conduct this test.  The Moss amp is conservatively engineered and can do this all day long.

Now for some bling.  These high-intensity white LEDs are super-glued into these brackets.  I wonder if this amp was a prototype?  I didn’t ding up these brackets getting them out.  They came that way.

To add some real intensity to that anemic internal illumination LED, this is a high-intensity blue LED I ordered for the occasion.

The aluminum bracket makes an excellent heat sink for the new high intensity LED.  I just used heat shrink tubing to keep it in place and to insulate it electrically where the wiring is attached.  The red connectors are male/female spade connector pairs that replaced the original ‘low-boy trailer light’ connectors Moss used, which I replaced because they were becoming intermittent.

Betcha’ can see this LED now!

LEDs check out.

In order to increase the current to the values needed by the white and blue LEDs, small appropriately-rated resistors were placed in parallel to the original LED bias resistors.  Remember that the value of two resistors in parallel is equal to the reciprocal of the reciprocal of their sums.

Wood screws hold the edge light LEDs in place, so that the LEDs shine into the Plexiglas.

A little black paint touches up everything so it appears that no one was here.  All wiring is new, with black insulation.

This is the finished product.  The blue light is really working for us to show off the interior, and the white illumination of the engraving is just what Zach wanted.  This works better with his white Tolex cabs.

Zach moved to Knoxville TN before the amp was ready, so I’m shipping it to him in two boxes.  One box holds the head in the case and the other box has all the breakable glass in it.

Here’s the glass.  Most of this box will be bubble pack.

This is the box of tubes.  Time for a cup of coffee, and another larger box to protect the glass!

Most ATA flight cases have foam, but this head case had none.  I’ll make do with bubble pack.

Good practice for Christmas!  This is the only pic I have of the rear cover panel installed.

And now we have gone full-circle, to the Big Buck again.  One more step!

Jen is holding the shippable box containing the glassware, and the case with the amp head is in the larger box.  Off to Knoxville where Zach has gigs and a contract waiting for him.  Best of luck to everyone!!

 

Thanks for reading all the way to the bottom!

David Latchaw, EE

281-636-8626

Vintage Tubes in a New Fender Blues Junior

The owner of this current-production Fender Blues Junior selected ‘vintage’ preamp tubes in search of the ultimate guitar tone.  A short time later, the amp doesn’t play at all.  This was not supposed to happen!  The Unbrokenstring Crew rides to the rescue to determine what happened.

This amp is less than a year old and is in excellent shape.  Let’s take a look inside to see what’s going on.

The first two preamp tubes are not JJ Teslas.  The customer said that he ‘had a buddy with a tube tester’ that sold him these ‘vintage’ tubes to give this amp that ‘vintage’ tone.  No kidding.

Oops, I did it again!  More amp porn.  No point-to-point wiring here.  This circuit board is a single-sided board with soldered jumpers to cross over traces.  Nothing wrong with this construction as it it mass-production-friendly.

How is this for ‘vintage?’  An honest-to-God made-in-USA tube branded RCA.

And how’s this for ‘vintage?’  Realistic is a Radio Shack brand.  They used to offer a ‘lifetime’ warranty on the tubes they sold.  Now, if you walk into a Radio Shack store, they don’t know what a tube is, and they will try to sell you a cell phone contract.  How things have changed!

The RCA tube failed in the tube checker in a rather unusual manner.  So here’s it’s new replacement.

The Radio Shack ‘Realistic’ tube was in excellent shape when tested on the checker, so I think we can safely say that the RCA tube was the root cause of ‘why this amp didn’t play’ anymore.

We’re all back together and playing.  But what would the customer think about losing his ‘vintage’ tone tube?  I showed him the video at http://youtu.be/ZYKISIQvBmw and he was all of the sudden very satisfied with the new tube and the tone of his amp!

 

Thanks for reading all the way to the end!

 

Contact:  David Latchaw EE

281-636-8626

This Engl Fireball Went On Strike!

 

This Engl Fireball head suffered a tube failure.  This sort of thing is usually not a big deal, but after the owner replaced the output tubes, a red “FAULT” light came on.  The amp played, but sounded a bit odd.  The Unbrokenstring Crew To The Rescue!

At first look, the rear panel is pretty simplistic.  However, let’s indulge in some Tech Porn and take a closer look.

OK, just a quick tour of the unit…  Here’s your typical IEC cord socket with integral mains fuse.

Footswitch jack functionality is straight-forward.

Interesting to note here is that the mix between the original signal (dry) and the stuff in the loop (effect) is set back here.  Since this control is on the back of the unit, it’s kinda ‘set and forget.’

So when this head reaches ‘end of life’ they want you to recycle it rather than just toss it in the waste bin.  Okay…

All you need to know is found here!

The output circuitry is very versatile; four, eight, sixteen ohms cabs, series and parallel, are no problem for this amp.

As the front panel is chrome, it’s a little tricky to make out the control nomenclature.  But very cool!

Not just gain, but Ultra Gain!  Is it a laundry soap?  Or more like A Clockwork Orange‘s ultra violence?

This amp has a ‘Power Tube Monitoring” circuit that indicates that a defective power tube has been isolated from the electrical power circuit.  This monitoring circuit protects the expensive components (rectifiers and power transformers) from further damage in the case of tube failure.  Oddly enough, something in the monitoring circuit went bad in this head, and now, known-good tubes still trigger the indicators.

Let’s take a look inside.  The quickest way inside is to enter through the back door.

With the back cover off, let’s unfasten the chassis from the amp cabinet.  This is a view of the bottom of the head.

These red LEDs add a little cheap bling to the appearance of the amp when it’s powered on.

Here’s another view of the bling LEDs.

The capacitors sticking through the chassis is kinda cool, but are a testimonial in favor of a good 3D CAD package.

These preamp tube shields are unique.  They clip through slots in the chassis itself.  A good squeeze liberates them.

Something new to me is the ENGL-branded preamp tubes.

Peeking around the backside of the front panel, we see the input jack and the end of the circuit board that carries the volume control and push buttons.  The braided sleeving over the power cable is a nice touch!

Here are the tone controls.  Note the flat ribbon cable sporting some hot glue as a strain relief.

 

Note the split ground planes in the circuit boards.

See the long metal straps that make electrical connection to the front panel LEDs, hanging under the circuit board?

The power transformer, sporting a sharp brass shield over the outer winding.

The output transformer lives under this steel shell.  It is attached to the circuit board, so all this comes off in order to remove the circuit board.  The weight of the output transformer makes the subsequent dis-assembly a little awkward.

The components we want to look at are on the other side of this large circuit board.

Many of the wires attached to the circuit board are ‘lap’ joints.  A little strip of RTV relieves the strain on the joint.

The low level circuitry is shielded by this steel sheet.  I’m removing it to get it out of the way.

Some of the lead dress will be loosened to allow the main circuit board to be inverted for service.

Rather than disturb a lot of solder joints, I just unfastened some of the smaller assemblies to free the main PCB.

This little resistor became a fuse, protecting the rest of the amp during tube failure.

This shows a little smoke, frozen in time.  When the smoke leaves a component, the component fails to work.  Thus, in the electronics world, we recognize “Magic Smoke” as the ‘stuff’ that makes electronics work.

The body of the burned resistor has been de-soldered.  Note the identical circuit, for the other output tube, to the right.

I’m using isopropyl alcohol for the cleanup on the circuit board.

While I’m at it, I’ll collect and save the Magic Smoke found on the chassis.  This can be used to resurrect other components.  If you don’t believe me, send me an email via the contact page so I know you are still reading this.

The affected portion of the protection circuit was repaired, and the other channel was repopulated with matching components so that they will behave exactly the same way if they are ever called into action in the future.

New tie wraps complete the restoration of the lead dress.

Now we’re pretty much back together.  This is a nice view of the chassis.

Remember the LED bling?  Well, here they are at work.  They are BRIGHT!

Both tubes are push/pulling and the bias is perfect.  The clean section is VERY clean on this amp!

With the lights down low, the bling is just a little understated.  I like it, and it sounds good!

Thanks for reading all the way to the end!

CONTACT INFO – David Latchaw EE

281-636-8626 voice or text