The Unbrokenstring Crew is amazed at the tough life that this tweed Fender Blues Junior has endured. Yes, it doesn’t work at all. Can we bring this poor thing back to life?
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Brian salvaged this amp from the curb in front of a house in North Carolina while volunteering in the cleanup following Hurricane Florence in 2018.
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Water damage is clearly evident on the tweed fabric, with stains and mold inside and out. The glue holding the fabric on the amp has failed, particularly on the bottom half of the cabinet.
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Starting from the bottom up, we use hide glue to stick everything back down. The lacquer coating on the tweed fabric has saved it from completely disintegrating.
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We are employing hide glue because it is not water based; we don’t want to make the wood cabinet swell any more than it already has. The hide glue can be easily cleaned up afterward, even after it dries, with warm water and a rag.
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Here, we’re removing the chassis. Fortunately, the rust is not too bad on this chassis.
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Someone has been here before, and they probably didn’t have a Fender employee badge.
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Too much heat and rework has destroyed the plated-thru holes in the circuit board. We can repair this.
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The connections (called ‘nets’ in circuit board parlance) are restored with small bits of stranded copper wire, tinned and soldered in place.
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The heart of any tube amplifier is the output transformer. It bridges the gap between high voltage power, tubes, and the loudspeaker. This HiPot (high potential tester) is measuring a complete failure of the insulation between the primary plate circuit windings of the output transformer and the secondary loudspeaker windings. Surprisingly, the loudspeaker is fine!
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Hidden on the back side of the chassis, the output transformer has lived. And Died. Alone. In The Dark.
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Fortunately, The Unbrokenstring Crew has a supply of original parts for boutique Fender amplifiers and clones, from Texas Amplification stock. This nice example of original Fender iron fits perfectly on this chassis.
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Testing the 6BQ5 / EL84 tubes, on the other hand, produces a light show. The purple glow is ionized gas inside the tube, and the blue lights hitting the paper behind the tube are beams of uncontrolled electrons.
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The red filaments are the only colors that should be there. After these pictures were taken, I had to replace the socket adapter on my TV-7U tester because it melted internally. The rest of the tester is fine and was re-calibrated – with a new socket adapter.
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After the light show from testing the tubes, each section of the amplifier is tested separately, in order to discover any other collateral damage from either the water or the failed output transformer. This amp will be Good To Go once the glue dries!
AJ played this wonderful MusicMan combo amp, until it quit suddenly. He was aware of the Big Names in the music business that repaired these, but was there anyone local? D’oh!
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As you might expect, this combo has one 12 inch loudspeaker and has a fifty watt Class AB push-pull pair of 6L6 tubes. One vacuum tube serves as a preamp, and the rest of the amp is built with solid state techniques.
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This looks a lot like a Fender amp, doesn’t it? Leo Fender had sold the Fender company to CBS, but wanted to continue making instruments and amplifiers despite a non-compete agreement that he was required to sign as part of the deal with CBS.
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So the MusicMan amps were born. The Mid-shift switch indicates a slightly different tone stack design.
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IIRC, production was shifting away from the Fullerton factory to Anaheim, with offices in La Brea California.
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The rocker switch for the ground select function and a three wire power cord is evidence that the older design of Fender amps was changing to meet modern regulatory requirements.
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Of course, model numbers were entirely new, and serial numbers had little resemblance to the old way of doing things.
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I have no idea what the paper label to the right is for. Any ideas, anyone?
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The chassis is sound, if not a little cosmetically ‘challenged.’ We can blame the humid Gulf Coast environment.
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Another change from the Old Fender was this pilot light, which consists of a neon bulb and a limiting resistor. The package is held in with a push nut.
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Yet another thing we don’t see here is the iconic brass sheet upon which most of Fender’s controls and jacks are traditionally mounted.
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The wire harness dress is excellent as is the workmanship. The black switch is the Tone Shift switch seen earlier on the front panel.
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These front panel controls work smoothly and are noise-free.
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The Bright/Normal switch is found next to the input jack.
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The dual-section 12AX7 lives here. This amp has been re-capped, including cathode bypass capacitors and all electrolytics. I’m not touching any of this!
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The rear panel jacks are Switchcraft, the best you can get.
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This ‘death’ cap is original. The red paint on the solder joints is an interesting way to indicate that they passed QC. This makes it easier to see where past rework/repairs have been done.
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The fuse holder held a too-high value 32v automotive fuse. The correct 250vac 3A part is installed.
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Most of the preamp duties are done with operational amplifiers. Those connectors in a square configuration are for the reverb tank and pedals.
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This unit is very well built and maintained.
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Can you see the problem? The pair of transistors on the pink heat sink form a phase inverter that drives the output tubes. In the 1970s, televisions, ham radio gear, and other consumer electronics were commonly built using ‘hybrid’ techniques e.g. solid state parts with power tubes. Leo Fender knew his TV stuff, and applied that technique in his new line of amps.
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These high powered resistors are part of the phase inverter circuit. They must be matched closely for good performance. Obviously, these are no longer matched.
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The devices on the heat sink are 75 watt 15 ampere 80 volt power transistors. They should be closely matched for best sonic performance. Also, transistors will drive the next (tube) stage with a bigger voltage swing than two sections of a vacuum tube, because they are inherently lower impedance.
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The main board is coming out of the chassis so that we can solder and desolder parts.
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In the late 1070s, circuit board design was performed on computers. Thus, graphical images could be added to the artwork. Also, this circuit board is electrochemically plated tin, which is a fresh new technology not previously seen in Fender products.
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On a lark, we will measure the value of the remaining 6.8 ohm resistor.
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It reads a little high. No problem. The resistors will be replaced with a matched pair.
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The old transistors are coming out for testing.
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The transistor curve tracer shows that this part is good.
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The other part is shorted internally.
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The heat sink is removed and the old resistors are desoldered. Here, we’re cleaning up the circuit board where the resistors go.
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These two parts were sourced from new stock and selected because their value matches better than 0.1%.
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These transistors were sourced from new stock and were matched on the curve tracer. See the new resistors above and to the left?
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The solid state phase splitter drives the tube stage as it should.
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The tubes are in and it’s time to fire it up!
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This amp comes with the official MusicMan pedal, controlling reverb and distortion.
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When a function is selected, the LED comes on. This is nice on a dark stage!
Andy found a ‘beater’ Silvertone amp on eBay and was curious if it could be restored. At first look, it was pretty rough. But could the Unbrokenstring Crew work some magic to undo the damage caused by UPS and previous amp techs?
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Danelectro built these amps for mail order distribution. In the 1960s, Amazon was a river in Brazil and the Internet was a military thing. But the Sears Catalog brought you nearly anything you wanted.
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The Sears catalog number was the URL of merchandise. With that number, the world was your oyster.
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The split splined shaft on the reverb was broken, and the original knob was long gone. The control does work electrically, but the reverb function was not functioning. Or something like that.
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The main volume knob was missing, because the split shaft was compressed and didn’t have enough remaining ‘bite’ to retain the knob. This could be repaired.
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One of the preamp tubes is a Chinese 12AX7. That tube tested bad.
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However, the rest of the tubes were in fine shape and were kept in service. By the looks of the power transformer, I believe that this amp was dropped on its end, because the transformer is leaning to the right.
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One of the preamp tubes is original, a Silvertone 6FQ7, made in U.S.A.
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The chassis is hand-wired. We are starting at the preamp section. Those brown capacitors are mica capacitors. Wherever two of them are next to each other, they are taped to each other using black electrical tape.
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The pilot light is good. The red and blue wires to the right are all shielded signal cables. Power wiring is on the left.
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The transformer on the left is an interstage coupling transformer. Masonite, a pressed fiber board material, is used extensively in this unit. Here a big chunk runs right down the center of the amp chassis, and many terminal strips are riveted to the Masonite for mounting components.
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The red cylinders are the filter capacitors, and the small silver cylinders are the power rectifiers. Amazingly, the filter capacitors required almost no reforming. Normally, capacitors this old are replaced out-of-hand, but the owner preferred to keep it as original as possible.
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Each and every capacitor was screened for leakage at working voltage and capacitance value. Do you see the scorch mark?
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At this end, we can barely see the output transformer, which has been replaced with a service spare part. Apparently the output transformer failed at some point, leaving some scorched areas behind.
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These blue wires come from the non-functional reverb tank.
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These wires come from the other end of the reverb tank. So we can guess that the reverb tank failed, and some Jake Leg tech just cut it out of the circuit rather than fix it.
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So, we will fix it. Note the duct tape holding the whole arrangement together.
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We find more Masonite under the tape. Each end of the spring in the reverb tank is stretched between the end clips.
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A second point of contact intersects the spring about an inch away from the end. Note that this contact is bent. This is another indication that the amp was dropped on its end.
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In the middle of the spring, this wire guys the spring at the center of the tank.
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So we bend the bent contact so that it pokes into the spring where it belongs. A very high voltage signal, over one hundred volts, is applied to the contacts at one end. The insulating cardboard on each contact keeps the current from flowing through the spring. However, the high electric field induces a mechanical motion into the spring, which is carried through the spring and wiggles the two contacts at the other end. The wiggling contacts act as a variable capacitor. The change in capacitance causes a varying voltage to be produced, which is amplified and sent to the amp. A moving ribbon microphone or condenser microphone works the same way.
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Simple enough, huh? Speaking of simple, we have Upgraded this reverb tank from duct tape to wire ties. Which is kind of a big deal, if you ask me.
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The reverb tank lives here. But the chassis is filthy. Now is the time to clean it all up.
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A rag is soaked with a combination of solder flux remover and furniture polish, which is tough enough to cut through six decades of crud.
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The reverb tank is suspended over the chassis with this bracket. It just bolts on.
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A replacement control has arrived. These stamped sheet metal nuts are used to keep the controls in place. The controls are all recessed behind a trim panel. The recessed trim panel makes it a challenge to find knobs that will work on this amp, as we will find out later.
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Here, the replacement control has been lubricated and will be wired into its new home.
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The reverb control has an ON/OFF switch that literally disconnects the reverb tank from the rest of the amp. The two terminals on the back of this control are the ON/OFF switch terminals.
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That sheet metal nut will not take much torque, so it is being tightened by hand.
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Next, we will replace this two wire line cord with a three wire cord, so no one will be electrocuted if the power transformer insulation fails.
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Two of the line cord wires go to this convenience outlet. The outlet will remain in place, but will be removed from the circuit.
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The power switch wiring is being modified to switch only the ‘hot’ wire. The neutral and ground wires will not be switched, per UL requirements. Also, the ‘death’ cap will be removed from the circuit, so that, when it fails shorted, raw 120VAC will not be connected to the chassis. You will find that important if you are holding the guitar at that moment…
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Let’s see what we can do about wiring in the reverb tank. These blue twisted wires are snaked through the chassis and will be attached to the terminal strip in this picture. Here is another good look at a pair of mica capacitors taped together.
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The little terminal strip in the middle of the picture has the remnants of the original blue reverb tank wires left from where the previous tech disconnected the reverb tank. So now we know right where to reattach them.
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Another reason to love eBay is that, from time to time, the Correct knobs can be located. These were surprisingly affordable. Some of the original knobs were repaired with Super Glue and reinstalled.
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The unit is back together and ready for final test!
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Finally, the Correct knobs really improve the cosmetics of this fine old amp head. The owner wanted to leave the film of rust on the front of the unit, for that Vintage Mojo look. This head sounds fantastic, but the piezo electric reverb tank sounds like something from a Star Trek special effects soundtrack, which, might be just the sound you want!
Richard relied on this unit for much of his sound, and when it went dark, he had to get it fixed or change his entire setup. Could the Unbrokenstring Crew bring it back to life and preserve Richard’s workflow?
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Our Cajun neighbors designed and engineered the mixer.
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Two screws hold on the side trim pieces.
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Once the screws are removed, the whole trim piece slides to one side and all these machined studs come out of the slotted holes. Nice.
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These side panels provide most of the mechanical strength of the finished assembly. Lots of little black screws hold them on. The red plastic tray on the right keeps them off the floor.
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Inside the panels, we see tell-tale signs that the Magic Smoke has been released. Please understand that Magic Smoke is a very, very technical term.
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Whenever the Magic Smoke is seen escaping from electronic components, they stop working. Therefore, all electronics must operate based on the principle of Magic Smoke. And you thought it was voltage and current…
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The fasteners used throughout the unit are tiny Torx machine screws.
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Sooner or later, all those knobs will need to be removed. For now, we will just remove the top row of knobs.
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Now we can separate the rear of the unit from the front and back.
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Power and data go thru these cables. I snapped a pic to be sure that they are oriented correctly when the unit is reassembled.
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The brick red connector is a push-on terminal that connects the chassis grounds together. It must come off, but it’s in a recessed spot between circuit boards.
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But the chopsticks came in handy and the ground terminal is free.
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More pics to document where the cables go.
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This is where the AC power is applied to the power supply assembly.
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The safety ground is the green and yellow wire. AC hot and neutral are applied via the mesh-covered cable on the right. A fuse, surge suppressors, and a temperature-dependent resistor are seen here, along with AC-line-rated filter capacitors and a filter choke. BTW the fuse is fine.
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AC power is rectified and stored in the large capacitor in the foreground. The rectifier array is seen between the yellow blocks in the lower right hand side of the circuit board.
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After years of service, the capacitors are swelling. Look at the top-facing end of the black cans seen in this picture.
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When electrolytic capacitors swell, the chemicals inside are reaching end-of-life. The capacitor begins to dissipate more heat and energy storage in the capacitor itself become less efficient. And this cap is next to a heat sink, which likely is warmer than the surrounding areas on a good day.
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More swelling. These eventually pop and make a huge mess.
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Looking at the reflection on the top of this device, we see signs that Magic Smoke escaped from this part.
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This part is a power field effect transistor (FET) and will be changed out. Electrically, each pin is shorted to the other.
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Magic Smoke has escaped from the end of this diode.
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More magic smoke was seen in the vicinity of this part. These are cheap enough that it will be replaced.
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Here is the new power FET, ready to be bolted in place. Only after the FET is fastened in place will it be soldered to the circuit board, assuring us that the solder joints will not be under mechanical stress.
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I tried to match components, but this big red gaudy storage capacitor was the only color available. Esthetics Fail. Sorry.
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Every electrolytic capacitor in the power supply was changed. The suspected bad semiconductors have been replaced as well.
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Fortunately, whoever did the circuit board design silkscreened the voltage values next to the pins where these voltages can be measured.
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Armed with that information, we can test the power supply and verify that it is functional before connecting anything else that may be damaged if the power supply is not functional.
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We are ON THE AIR! Everything works as it should. Except…
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Can you see the cloudy area on the left edge of the LCD? That is not a reflection. That is more Magic Smoke. The LCD is fully functional, but this is just plain unacceptable.
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To gain access to the LCD, we need to disassemble the keyboard portion of the unit. And remove the rest of the knobs.
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With more screws removed, we have access to the LCD assembly.
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Opening the LCD allows for the inside of the lens to be cleaned and polished, removing the Magic Smoke.
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While the keyboard is apart, the sheet metal panel can receive a little TLC.
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Aw, what the heck. While we’re here, let’s inspect the remaining circuit boards, looking for aging capacitors and signs of Magic Smoke.
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An effects processor IC is seen here, along with many hybrid analog gain blocks. No schematic would help us through this maze. But everything here is in Tip Top Shape.
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Reassembling the panels together is best done with the unit on its side.
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Having the unit on its side allows access to all the internal cabling that needs to be reconnected. Glad that we had all the pictures!
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Some of the small cables need to be reconnected at the last step as they are barely long enough to reach their destination.
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Oh, and here’s that chassis ground terminal. We got it apart somehow…
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So here we see it almost mated. This step was completed with some very long needle nosed pliers.
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With the LCD cleaned, this unit appears ready to test again.
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All functions work. All lights light up. Life Is Good!
In Part Three of this project, The Unbrokenstring Crew installed a unique cut-out switch in the pick guard of this guitar. One more thing… Now that the instrument is play-able, the original plastic Squire nut is cracked. Grrrr…
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The old Squire nut came out in pieces.
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Let’s make a new one from Vietnamese water buffalo bone. The blank we’ll use today is shown above the old Squire plastic nut.
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Not to brag or anything, but these bone nuts are truly a renewable resource that I am privileged to legally import from overseas. CITES can go bite it.
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The eighth inch chisel easily cleans whatever glue Squire used to install the original plastic nut.
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This slot is ready for the new nut.
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Sorry, that’s as clean as I can get it.
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The new blank nut is thickness-sanded to fit the slot. I’m doing this by hand because the blank is very close to the proper dimensions to begin with.
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The inside radius is established by using the actual neck as a radius block.
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The side contour is also established by hand, on the actual instrument.
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The actual height of the fret wires is measured in order to calculate the depth of the string slots. This dial indicator measures the installed height of the fret wire above the finger board.
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Here, we’re gluing the new nut right to the finger board using hide glue. A water-based adhesive could cause the wood to swell; shrinkage over the next few months as the wood dries out would throw off the accuracy of the nut slot depth. Can’t have that!
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The old nut is used as a template to establish string spacing. A couple of old strings are used to align everything.
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Now that we know the fret height, string gauge, and string spacing, we can begin establishing the string slots. At the nut, the string slot depth is constant across the radius of the finger board, regardless of the string diameter.
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With a set of old strings in place, the top of the nut can be quickly contoured so that the top of the nut will not protrude above the strings. The geometry of the top of the nut is established in part by the diameter of the strings, which is, of course, not constant across the radius of the finger board. This three-cornered triangular file belonged to my father.
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This old triangular file is just the thing to contour the nut further, smoothing out sharp corners and preparing the nut for polishing.
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Note that the string centers are just below the top of the nut, and that the top of the nut is no higher than any string.
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This is the instrument, as delivered. The Vietnamese water buffalo bone is a spectacular material for musical instruments: incredibly hard, uniform throughout its bulk, and capable of a fine polish without additional waxes or oils, making a visually attractive nut and providing a stable, polished string slot that allows for smooth and stable tuning without binding or sticking. What more could you ask?
I think we’re finally done with the Jagmaster Make-Over!
In part two of this series, The Unbrokenstring Crew converted this instrument to a Tune-O-Matic bridge with a Bigsby tremolo. Now The Unbrokenstring Crew will add a cut-out switch to this instrument.
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Matt has specified this exact spot where he wants the cut-out switch installed. The sharp point of an Exacto knife marks the exact center of the hole where the new switch will reside. Because that’s why they call it an Exacto knife.
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We need to remove the pick guard, so off come the strings. Again.
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This nylon washer is used in the Bigsby system to, among other things, set the working height of the lever. Keep track of this!
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A pilot hole is bored where the Exacto knife made the mark seen earlier.
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The copper foil around the new switch hole is cleaned. We are now ready to install the new switch.
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The resistor is installed across the contacts to limit the audible ‘pop’ that you sometimes hear when switching low-level circuits, like the circuits found in guitars.
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Step Three is complete. This switch is not a push button, but is a spring-loaded momentary, center-off switch. Matt can quickly flick it from side to side for a very cool effect.
But wait! There’s more! In the last installment of this project, the cheap Chinese plastic nut has cracked. Tune in to see how The Unbrokenstring Crew upgrades the nut. Like A Boss.
In our first installment of this project, The Unbrokenstring Crew installed some new pickups in this cool offset-waist Jagmaster. Now, The Unbrokenstring Crew takes a deep breath. The inserts for the Tune-O-Matic will fall right at the edge of the body route for the Fender tremolo block. Extensive modification of the body is necessary for the next steps.
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So The Unbrokenstring Crew takes an inspiration break. The first Fender-style guitar we’d seen with a Tune-O-Matic bridge was Larry Carlton’s Valley Arts ‘Strat’ copy, seen at about 9:10 in this video from 2012. WARNING: lots of funny Guitar Face to be seen throughout the video.
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To position the TOM (Tune-O-Matic) bridge, we need to verify the dimensions of the guitar.
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The twelfth fret is just to the right of the fret board marker. If you double that measurement, you get the ‘scale length’ of the guitar.
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This metal machinist scale is eighteen inches long, so to complete the measurement to the bridge, we moved the end of the scale to the twelfth fret.
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You will see that the existing bridge saddle blocks fall around the same place on the machinist scale. This looks good so far.
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It’s time to get serious. The patient is prepped for major surgery. The black wire seen in the picture is the spring claw ground and the ground wire for the pickups.
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The claw is coming loose and the springs will be removed.
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After the new bridge and tremolo are installed, we won’t be needing this claw anymore.
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With the spring tension gone, the original bridge just falls out. These inserts, though, should be tight, and they are not.
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Both of the inserts had broken out. This points to the main concern with this modification e.g. how to install new inserts for the TOM bridge, in the right place, with enough wood around them to assure mechanical stability and sustain. This was a significant question in the planning stages of this project.
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With the pick guard assembly temporarily in place, we can begin to establish the geometry of the new parts.
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The outline of the pick guard is lightly traced on the surface finish of the instrument. The starting (and ending) finish is matte black. This gives us considerable flexibility when doing the modifications and refinishing the instrument when modifications are finished.
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Some tape holds the machinist scale in place, leaving our hands free to do some marking down on the body.
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The TOM bridge will go about here. Guitar Cognoscenti advised that the TOM bridge should go about 8/64ths of an inch beyond the 1x Scale Length for the instrument, because of the increased string length which occurs when the string is deflected when fretted, and other effects. Thus, the mark for the center line of the TOM bridge is at the 12 and 56/64ths point under the machinist scale.
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The measurement made in the previous picture is expanded across the battle space so that the TOM inserts can be properly placed. Do you see the issue with the new TOM bridge placement?
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While we have the 24 inch artist’s scale out, let’s check to see what sort of clearance we have under the plane of the fret board to verify that the TOM bridge will fit. If it doesn’t fit, we can shim the neck up a bit and create more clearance.
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The exposed end of the ruler gives us an idea of where we are on bridge and neck geometry. This number goes into the notebook for later. Oh, and we have both English and metric systems well-represented here.
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Let’s move to the other axis, and establish the actual center line of the guitar. A string is fastened at the nut between the D and G slots.
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The position of the neck is the determining factor of where the bridge shall be, not necessarily the guitar body; There will be room for adjustment later if we need it, but let’s get it right while we’re here.
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The center of the bridge is marked on the tape.
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Before we go any farther, the original bridge is placed back on the body as a sanity check for the work done so far. As if sanity had any meaning at this point…
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Another number to go into the notebook is the original string width at the bridge. As we planned, the TOM bridge string spacing is really close to this measurement.
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The breakout from the original bridge inserts need to be addressed, because we really want as much solid material in this area as we can get.
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Both inserts broke the body out. Some instruments are best repaired by just router-ing out the entire top and substituting a slab of maple. However, with the routes on the back side, nothing would be left of this guitar body.
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These chips will be glued back where they belong, using hide glue. We avoided using a water-based adhesive such as Tite-Bond because the wood would swell from the water, then gradually shrink again over the next few months, rendering our efforts to fill all the cavities moot.
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This damage is repaired well enough to support the steps to follow.
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Birch is the less-beautiful cousin of maple. It has very little figure, and is very straight-grained. These birch dowels are perfect for filling the original holes where the inserts were installed.
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After adding some protective tape, the dowels are cut flush with this Japanese saw.
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I like this saw. So you are going to see lots of pictures of it today.
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I think you get the idea now. Yes, I like this saw!
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The blue strip that you see is the edge of the blue masking tape seen above. Note how close the edge of the routes are to the center line of the new bridge. All this needs to be filled-in so that the new inserts can be secure.
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We will work on this side for awhile. The neck is off and is out of the way.
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Much of the paint in the interior of this body is conductive shielding paint. Paint is not a good surface to glue anything to, so the Dremel tool and a sanding drum removes it all. This body is actually some very nice wood!
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Paint is removed all the way around the tremolo block route. No electronics will go down here, so I’m not worried about shielding.
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The tiny lip remains at the bottom of this route. This lip is actually on the front face of the body of the guitar. The Unbrokenstring Crew will leave it in place as a depth guide when installing the filler blocks.
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Since the neck was off, we took a moment to clean up the bottom of the neck pocket. A clean, hard neck pocket is essential for good guitar tone and sustain, as it forms the counter-spring for the strings themselves.
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Only the bottom was scraped, and then only enough to remove any soft, crumbly finish. The sides remain unmolested as they establish the geometry of the guitar, which we documented earlier.
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Two blocks will be fabricated to fill the trem block route. The paper patterns are on the left, and the block of spruce plywood is marked with the approximate shape to fit the route.
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These blocks are fitted to the original trem block route.
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The faces are cleaned up just enough to allow the glue to do its job when these are installed.
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These will stack into the body route. Do you see the little strip of glitter to the left of the spring route? That’s the original color of this guitar. Can you say “Glam”?
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We were able to source this NOS bridge from a company that purchases broken guitars from Big Box Retailers and separates the brand new parts from the firewood.
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This is the first meeting between the new bridge and the guitar body.
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This brad-point wood bit makes a good center-finder. This bit is exactly the same diameter as the inside diameter of the stud hole in the new bridge. Everything is arranged so that the point falls on the center line drawn on the blue tape.
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A shallow marking hole is then drilled to mark the spot.
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This picture clearly shows the issue with adding a TOM bridge to a Squire body. There is no substantial wood around the hole where the inserts will be installed. Yet, we press on!
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One last trial fit is performed for these filler blocks.
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These plugs are ready to go.
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These are a good, tight fit into the original trem route. Can you see the glitter?
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The top side should be flush. The lip inside the route was left behind to align the plugs already in the body. Another piece of birch will fill this shallow cavity.
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This little bit of solid birch is fitted to the opening.
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Hide glue is applied liberally and the stack of filler blocks are glued into place.
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With the glue dry, we are ready to keep moving on this project.
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The top is masked off again so that the top of this filler block can be completely level with the rest of the guitar.
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A cabinet scraper brings the top of the filler block down to the level of the top of the guitar, or at least to the same level as the masking tape.
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We cheated and used some wood filler to close up all the gaps. This will be finish sanded after one more coat of filler.
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For additional internal strength and rigidity, another block is fabricated to fill a bit more of the spring body route. The same birch plywood is pressed into service.
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The new filler block is a very tight fit. The paint around it will be sanded away so that the glue around the block can bond directly to the wood of the guitar body.
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This new filler block is now glued into place. You can see a layer of hide glue on the filler blocks already in place in the trem block route.
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The matte black finish was matched, leaving only the pilot holes for the new TOM inserts. All of the remaining body routes will be foiled and grounded at the output jack. We are covering some interesting shapes today!
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The pickup cavities are done.
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The control cavities are completed. The copper looks spectacular against the matte black of the body of the guitar. Here you can see how the matte black finish came out over the unfinished filler blocks installed previously.
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While we’re at it, let’s do the underside of the pick guard. Note that the seams of the tape are tack soldered. The seams inside the body are also tack soldered, to form a continuous shield.
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A small tab of foil extends from the body routes so that the foil under the pick guard can be bonded together using a pick guard screw for compression.
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Next, the holes for the inserts will be bored using this brad-point bit.
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The tape marks the correct depth. We don’t want to drill all the way through the guitar, do we?
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I couldn’t help myself. I had to place the new bridge where it goes just to gratify my curiosity.
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And while I’m gratifying myself, let’s check the position of the Bigsby.
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As we begin slowly boring the holes for the inserts, we can clearly see the boundary where the body ends (on the left) and the filler blocks begin (on the right.) This is one spot where we need the most strength and rigidity for best tone (and to keep the guitar from falling apart under string pressure.)
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This aircraft drill bit is boring a passage for the ground wire that will engage the bridge insert. To the left of the picture is another dowel rod.
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That distant dowel is in a hole on which the Bigsby is mounted. Using the eighteen inch long aircraft drill, we need to slant drill our way through the guitar body and hit that hole. Somehow.
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More blue tape indicates just how far I must drill through the body. If I don’t hit the dowel by the time the tape hits the copper, I missed.
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Inhale. Exhale. I hit it! Some wire left over from the spring claw is pushed through the holes drilled in the previous pictures. Yes, that wire made a ninety degree turn inside the body of the guitar. Kind of a big deal.
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Using the Exacto Knife, the insulation on the wire is nicked in the proper spot so that the insulation can be removed, allowing the wire to touch the bridge insert, thus grounding it.
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The insulation is removed so that the wire can form a compression joint with one of the bridge inserts, thus grounding the bridge.
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The big clamp can apply plenty of force to seat the bridge insert. The one on the far side has already been pressed into place.
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The ground wire is now joined with the wire from the pick guard shield and soldered to the foil in the control route.
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The free end of the ground wire is stripped and ready to be compressed against one of the Bigsby mounting screws.
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When the Bigsby is installed, the screw that goes here will compress the ground wire and make the electrical connection, thus grounding the Bigsby tremolo and strings. No wiring will be visible from the outside of the guitar.
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Here is the newly-installed bridge and trem. The pick guard is placed temporarily for this picture. This project is shaping up well!
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The Correct pick guard screws are now in hand and will replace the larger screws originally used on this guitar. The holes are partially filled with birch dowels and cut flush.
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The exact center of each pick guard screw hole is established with this pocket drill bit.
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Once the center is established, the hole can be bored using the Correct bit.
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This was a goof. The outside of one of the TOM bridge inserts interfered with this corner of the pick guard. The drum sander on the Dremel tool corrected the oversight.
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Here, we are finishing up with the pocket drill. I use the electric screw driver as a drill because it is slow and easy to control.
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This is a good shot that shows the modification of the pick guard to fit the TOM bridge insert.
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To assure that the studs fit snugly in the inserts, some copper foil is used as a shim over the threads of each stud to make electrical contact and to help lock the stud in place after adjustments are made.
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Copper foil is added or removed until the stud fits snugly regardless of how much of the stud is threaded into the insert.
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Little bits of copper foil are all it takes to get these studs shimmed up where they belong!
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It’s time to string it up!
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It’s a lot easier to get the strings on a guitar with a Bigsby if the ends are pre-formed to wrap around the roller.
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TOM bridges are versatile insofar as the saddles can be removed and turned around to extend their adjustability. Note: do not lose these little clips. Don’t ask me how I know this.
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Once the clip is off, the adjustment screw can be unthreaded from the saddle.
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The bevel on the top of the block can go either direction. We can use this to our advantage when setting intonation.
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This saddle has been turned around.
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The screw keeps the saddle in place.
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And the little clip keeps the screw in place. Again, don’t lose these.
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We took a detour to de-burr the hole in this tuning machine. This tuning machine was masquerading as a string cutter. The Unbrokenstring Crew will not tolerate broken strings!
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Step Two is complete. This guitar is a lot of fun!
In the third installment of this saga, The Unbrokenstring Crew will install a cut-out switch in this instrument, which silences the guitar whenever the switch is activated. However, this switch is not just a normal push button. Tune In next week for Episode Three!
Matt has many dreams. One of them was to have an offset-waist guitar with a Tune-O-Matic bridge and a Bigsby. And while we’re at it, a fresh set of pickups. And then, of course, a kill switch, because, why not? And there is Even More after that! This sounds crazy enough for The Unbrokenstring Crew to immediately roll up our sleeves!
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And, yes, Matt is a star!
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We have some added confidence that we can go crazy with this project because this is not the most expensive guitar in the world. But, as we shall see, it is a surprisingly good base for the modifications in mind.
Starting with the pickups, these factory humbuckers will be changed out.
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Each factory pickup measures almost the same resistance, but we labelled them separately for the benefit of future generations.
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A pair of P-94s grace the pickguard.
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The Gibson P-94s look dazzling on this guitar! Matt really hit a home run in the esthetics department. And they sound awesome, as we will later find out.
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A quick test of the wiring is performed by gently tapping each pickup with something metallic while the little Orange amp turns my taps into sound.
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While we’re here, the pickup selector switch is tightened with this serrated nut compression tool.
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Step One is complete. This guitar looks pretty snazzy!
In the next installment of this saga, The Unbrokenstring Crew will take a deep dive into serious Bod Mod and install a Tume-O-Matic bridge and Bigsby tremolo on this instrument. Tune In next week for Episode Two!
This unit came in to the shop with intermittent signal and power issues. First, we need to get this unit functioning consistently. Only then is it possible to find other issues that need attention. Could The Unbrokenstring Crew have a look at it and bring it back to its full potential?
This all-tube unit looks too new to have any problems at all. Sure enough, it did not power-on as it should. Let’s take a look at this unit before we open it up.
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Many features are packed into this little guy. And I love the color!
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Bringing out the Send and Return functions adds versatility when using effects. And there are plenty of jacks for connecting speaker cabinets.
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The Name/Rank/Serial Number picture helps when ownership changes. The Unbrokenstring Blog has already identified one piece of stolen gear.
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Remove-able IEC line cords are always nice. But how do we set the AC line voltage? I see an ink mark, but no switch.
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When we pull the case off, we are greeted with a pleasant sight of all tubes (and solid state rectifiers under the chassis.)
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Cruising around the sides, we find something of interest!
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Here is the switch to set the AC mains voltage. D’oh!
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Other than the fact that the tube sockets are soldered to the PC board, there is very little to dislike regarding the design and layout of this unit.
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The power supply section appears to be in good condition. The solid state rectifiers are to the left and up from the green PASSED sticker.
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From left to right, we see the ON/OFF switch and the power level setting switch, the pilot light, volume control, and the bass tone control.
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Picking up again from the bass tone control, we see the MID tone control, treble tone control, and the GAIN knob.
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Next to the GAIN control is the input jack. These jacks switch signals when no plug is inserted, so we need to check the operation of all these jack switches once the unit is operational.
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The power fuse looks good, if not a little saggy. We should check it electrically.
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Well, what do you know? This fuse has been storing up a lot of Ohms; in fact, over two million ohms (which is more than my meter will measure.)
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This spade connector has come loose. It could account for this unit not working, as well as the fact that the fuse had open-circuited and begun accumulating all those Ohms…
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These switching jacks are the source of the intermittent audio. They are all cleaned with DeOxIt and cycled several times to renew them.
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After a new fuse and after cleaning the switching jacks and reattaching the loose wire, this unit is 100%.
The fuse blew in this Sunn Stinger 20, but the new fuse blew as well. Then, it quit working for good. Cool Under Fire wanted this combo amp back in action. Could The Unbrokenstring Crew sort it all out?
Our patient still has that cool Sunn vibe after all these years, even if it doesn’t work. That name badge is recognized by all.
Getting up close and personal to the front panel, we see an input jack and three tone controls.
Independent Gain and Volume controls show that this unit means business! The mute button and headphone jack give this amp a family-friendly advantage over other inexpensive practice amps.
As is found on many guitar amps, the cabinet is sealed with a closed back.
Oh no! The sticker says “DO NOT OPEN.” What are we going to do?
We open it, of course. How long has it been since you’ve seen a loudspeaker with a square magnet?
Obviously this is a four-ohm loudspeaker.
The steel chassis has circuit boards for the preamp functions, just behind the controls, and power supply and audio power amplifier at the rear of the unit. Nothing appears out of order here. No, wait! Look here!
This wire has come un-crimped from the terminal, seen in the background.
We can just open this terminal up a bit, re-insert the wire, and solder it in place. But the question remains: Could this have been the reason that the unit blew fuses before it finally quit permanently? I don’t think so.
While we’re waiting on a copy of the Sunn Service Bulletins for this amp to come via email, let’s take a minute to clean this unit up.
The controls hold the front edge of the circuit board in place, and a couple of screws hold the back edge steady.
The headphone jack is entirely isolated from the chassis of the unit. Even though the chassis is wired to the green wire safety ground in the AC cord, taking measures such as this makes the UL Certification easier.
The input jack is shielded from interference with this metal bracket. This kind of additional shielding is almost never done on inexpensive amps… this Sunn is definitely a Cut Above!
The switches and controls are easily cleaned now that they are easily accessible, as shown here. The Unbrokenstring Crew NEVER forces cleaning fluid around the shaft of the potentiometers as a cleaning procedure, because dirt and old lubricant is forced inside the control. It cannot end well. Sorry, StewMac.
With all the hardware out of the way, it is a trivial matter to clean up the face plate. Gibson Guitar Pump Polish is pressed into service for this step.
Reassembly also involves tightening the woodwork. Over time, wood shrinks (even in humid South Texas) so most amplifier cabinets will develop buzzes and rattles as they age.
Maybe if we work quickly, the “Do Not Remove” police will not catch up to us and put us in jail.
The Service Literature arrived! It states that the next-higher ampacity of fuse should be used in this unit; There was an error at the factory wherein units in this serial number range had an inadequate fuse installed! This little amp has run for hours with no issues!
