Ampeg BA115HP Combo Rescued from Pawn Shop

This pawn shop find doesn’t work, parts are rattling around inside, and a knob is missing. Watch The Unbrokenstring Crew get this into the practice room!

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St. Louis Music moved their production to China, which IMHO was the beginning of the end of this fine brand. Que sera sera.

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I had always wondered if stuff from a pawn shop with obscured serial numbers was a ‘little warm to the touch,’ if you know what I mean. But who would steal something this big?

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The electronics are out of the cabinet for inspection. A replacement Gain knob is on order from eBay, because someone cranked it up and ripped off the knobs. The ‘Style’ switch, which was broken internally, was put on order as well.

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This amp sports three band EQ and a Master Volume

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You can play your CD through the Line Input RCA jacks on the top, and mute the amp to play through headphones. In the muted mode, a built-in chromatic tuner comes on. Neat!

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The internals of the tuner was one item rattling around inside the unit.

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The translucent lens over the LED array diffuses the individual LEDs that illuminate when each note is played. This was very dirty for some reason.

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The tuner electronics and LEDs are one assembly, which makes me think that this was an option for this model.

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This power cord needs attention. All I need to do is unclamp it, shorten it, and re-clamp.

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The Chinese did not go cheap on the power transformer. This is the power supply section, with the filter capacitors seen on the left.

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The power amp is all bipolar transistors. The large white objects are wire-wound resistors. Some of these resistors are open-circuit, but the transistors are all intact. This is interesting…

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Removing the preamp board, we note that these spacers are required behind the input jacks. The gain control, which needed a knob, is fine.

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Speaking of spacers, this toothed washer is required behind the Style switch (the white and green item in the center of the picture) to properly set it’s geometry. This is the new switch. The original switch was defective.

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The ‘sleeve’ contact on this input jack was open-circuit, which caused hum with nothing plugged into the amp. Do you see anything?

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The contact on the right is not closing when nothing is plugged into the jack.

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The easiest way to fix this is to just replace the jack, although these can be carefully disassembled and bent back in place. These are inexpensive enough to just replace.

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The open resistors were identified and removed. Note the round holes in the circuit board.

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These round holes are for air circulation. I believe that there is a relationship between the plugged holes and the defective resistors.

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Some of the holes were plugged. The material plugging the holes is adhesive that helps to mechanically support the resistors when the amp is moved. Someone at the factory was sloppy with the hot glue gun!

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The new replacement resistors are modern high-temperature resistors, spaced above the circuit board for additional heat dissipation. All of the holes in the circuit board are clear now.

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This part of the circuit board is all cleaned up and ready to reassemble.

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The raw corners around the mute button can be stained to match the black anodize aluminum. A permanent Sharpie pen works well for this task. A little blending with a finger, before the marker fluid dries, makes the repair invisible.

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The front view of the finished unit is pretty unremarkable, since the controls are on the top and back. The control in the lower center is a pad for the tweeter. This unit is now 100% and ready to get back to the practice room!

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

The Left-handed Squire Stratocaster Gets Upgrades

Lindsey wanted new Texas Special pickups installed in her beautiful Squire Strat. While we’re at it, we’ll upgrade the tuning machines to Fender Locking tuners. Note that this is a left-handed instrument.

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Name, rank. and serial number, please! As we disassemble this instrument, we will see that this Squire is just a little bit nicer than the instruments coming from China.

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This is a good picture of ‘break angle,’ where the strings are stretched over the nut.

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I just love the red pick guard with the red burst finish! The strings are off.

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Lindsey purchased a new set of Fender Locking tuning machines. The original tuners are coming off.

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This is a picture of a pile of retired Squire tuning machines.

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Oops. These new Fender Locking tuners use a little different mounting pattern than the Squire tuners they replace.

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Little dimples next the the dowel pockets show where the new dowel pockets need to be bored. So there IS a difference between the Squire tuners and the ‘similar’ but full-sized Fender Locking tuners.

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The new tuners are lined up with a steel rule, to get them absolutely straight.

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After plugging the original holes with ash and boring the new dowel holes, the locking tuners are in place. No one can tell now that any gun-smithing was performed. They look pretty spiff!

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True to its brand, this neck plate says “Squire.”

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To remove the pick guard, the neck must be removed. Why? Because the neck has an ‘overhanging’ fret board.

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What is a fret board overhang? This.

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The Unbrokenstring Crew will augment the shielding around the electronics by adding copper foil to the body routes and the bottom of the pick guard.

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The ‘ground’ wire to the conductive shielding paint is removed so that the copper foil can be installed underneath it.

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This triggers my Obsessive/Compulsive Disorder (OCD.) Did someone add a center spring and just push the black ground wire out of the way?

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This film tone capacitor is just fine for this application.

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The output jack is liberated from the ‘football’ plate. The jack and cable will be removed from the body entirely.

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This neck pocket is VERY clean and true, and requires no remedial work to remove finish or glue. This is NOT a plywood guitar! It appears to me that a black Magic Marker pen was used to color the corners near the neck to cover the raw wood.

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The CNC machine cut one direction around the cavities of this body, causing tear outs in the wood grain. Then, they were just painted-over. This needs to be cleaned up and smoothed out to give the copper tape a proper surface to which to adhere properly.

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Here we see some router tear-out because of the conflict between the rotation of the router and the grain of the wood. The router bit edges tear and lift the grain up and away from the body. When routing by hand, the correct procedure is the change the direction from which the router approaches this part of the wood. But you can’t tell a CNC machine to stop and work backwards. Well, you can, but only if the programmer is conscientious, rather than cost-conscious.

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The white material is left-over polishing compound, used to buff the finish.

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With considerable application of elbow grease, the body routes are clean and smooth. The black paint is electrically conductive and helps a bit to shield the electronics. But we can do better.

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For some reason, I always start the copper foiling process in the output jack route. Note the tabs that will later connect to the foil on the underside of the pick guard.

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The body cavity routes are foiled at last!

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Turning our attention to the electronics, we remove the nylon tie wrap which bundles all the wiring under the pick guard.

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The bridge and neck pickups from Squire are exactly the same, and have white wire insulation for the signal. The center pickup wire has yellow insulation.

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The Squire pickups are removed and bagged. Perhaps someone can use some new Squire Strat pickups in their FrankenStrat Build.

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This aluminum foil sheet will be replaced with copper tape. I have no idea what the “H” stands for. Is it an “I”? Or The One?

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We can still see the original protective sheet that covered the pick guard under the knobs.

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This aluminum sheet is easily removed with a fingernail.

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To save my fingernail, a tooth brush handle is pressed into service as a scraper. This foil is mostly paper, with an inconsequential layer of aluminum over it.

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The remaining tape adhesive is dissolved. This chemical wash treatment will leave a surface on this pick guard to which the copper tape will securely adhere.

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The pick guard gets the copper foil treatment. The holes in the pick guard are cleared of copper, and the strips of copper are tack-soldered together to form one continuous shield.

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To remove the pickups from the pick guard, the wires that were soldered to the switch are clipped. Then the remaining wire ends are de-soldered. However, this switch was broken (probably at the factory) and the terminal was broken off. The wire was soldered directly to the printed circuit board upon which the switch is built.

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Enough of the circuit board trace remains so that a solder connection can be made.

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The new Texas Special pickups are the correct size. However, the holes in the Squire Strat pick guard are sized for the more diminutive Squire Strat pickups. So, a little gun-smithing is in order.

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The pickups are installed and the pickup leads are dressed where they belong. We are ready for final wiring.

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Before we solder the pickup leads in place, let’s just see how these Texas Special pickups ohm out. The display on the ohmmeter is a little hard to read, but the neck pickup measures 7.02k ohms.

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The resistance of the middle pickup is 7.22k ohms.

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This is the Texas Special bridge pickup resistance.

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The jack is oriented in such a way that the contacts and the wiring cannot touch the copper foil shielding. If it does, the instrument can go mute.

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The wiring is fished back through the drilled holes in the body.

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Finally, my OCD itch is scratched. The claw ground wire is underneath ALL of the springs. This guitar is to be set up as a ‘hard tail’ e.g. the bridge is not floating but is pulled into a stationary position by spring tension.

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Here’s one last look at the electronics before the guitar goes back together.

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This finish and pick guard are just spectacular!

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With the strings off, it’s the perfect time to condition the fret board.

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Restring, setup, bring the pickup heights back to where they belong, and this beautiful guitar is ready to play!

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Fender Blues Junior Puts On A Light Show

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!

.Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

MusicMan RD50 Combo Amp Repair and Inspection

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!

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This unit is ready to go again!

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Sears Silvertone 1484 Amp Head Refurbishment

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!

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Fender Blackout Strat Becomes Even More Classic(al)

The original neck on this MIM Black Strat was made from wood that tended to twist when the string tension varied, either because of temperature changes or when employing different string gauges. It’s now time to take this guitar to the next level, and make it an iconic Blackout Strat

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The neck will be retired to another instrument.

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This instrument was built in 2006, which happened to be the 60th anniversary of the founding of Fender Corporation.

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The neck is off and headed to its new home.

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David Gilmour’s Blackout Strat has a maple fret board. This instrument will get a new maple neck, with a 59 ‘C’ contour and an almost 2 inch wide nut. With light strings, this guitar will feel like a nylon-stringed classical guitar.

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The aftermarket Fender tuners are lined up with the machinist’s rule and tightened into place one by one.

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These tuners are ‘locking’ tuners, which positively grip the end of each string in a clamp. This is necessary on this instrument because of the very light gauge strings we will be using.

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Head stock and nut are ready to go.

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The middle pickup appears to be not working. Let’s take a look inside.

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Sure enough, there is a broken wire inside the pickup cover.

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The break in the wire is literally in the very last turn! So one turn is un-spooled and threaded through the eyelet where it belongs.

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As was done at the factory, the wire end is pulled through the eyelet a few times and soldered in place.

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The middle pickup is tested and is right where it should be.

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The Classic(al) Blackout Strat is strung with 7 gauge strings; Yes, not 12s, not 10s, but with Billy Gibbon’s own Dunlop Reverend Willy Extra Light Electric Guitar Strings, .007-.038. With the proper setup, this instrument has the play-ability and feel of a nylon-strung classical guitar. Thus, we have the Classic(al) Blackout Strat.

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

PreSonus StudioLive 18.0.2 Mixer Is Resurrected from the Dead

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!

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Fender MIM P-Bass Gets Upgraded Pickups

A famous Houston Jazz Cat sought out the services of The Unbrokenstring Crew after hearing about us by word of mouth. This instrument was at home on the stage and in the studio, but just needed a little something more. Could The Unbrokenstring Crew supply that ‘little something more’ and get it done before this Friday’s gig?

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This instrument was a dead-stock, straight-ahead jazz bass, just a little funk added in for fun.

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We will reuse the strings, so they are just pushed back through the bridge to get them out of the way. The original bridge pickup is already loose from the body.

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A peek under the cover shows the smooth, unscrambled, automated winding used on these factory pickups.

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To access the neck pickup and get to the wiring more easily, the pick guard is removed.

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Black and white wires go to the neck pickup. So far, so good.

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And, black and white wires go to the bridge pickup. We need to keep all these wires straight. Or gently curved, as the case may be.

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The burned insulation and cold solder joint on the tone pot tells me that the factory wiring was done in a hurry. The Unbrokenstring Crew is in a hurry, but not this much of a hurry.

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The original neck pickup ohms out at 5.14k ohms.

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The original bridge pickup is not that different, measuring 5.51k ohms. The original pickups were labelled and returned to the owner.

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Our Jazz Cat chose these pickups for his instrument.

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Rio Grande pickups are built here in Houston, Texas. FYI, for the last five years, customers of The Unbrokenstring have asked to have Rio Grande pickups installed in their instruments more than any other brand.

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The Unbrokenstring Crew is curious about how these new pickups measure up. On the screen of the Fluke meter is the resistance reading of the new neck pickup. A lot of wire is used to make this pickup!

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This is the resistance of the new bridge pickup.

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Wiring for the bridge pickup is snaked through the bore in the body, along with the cavity ground wire. The pick guard does not cover this part of the instrument, so cavity wiring needs to be tunneled through the body.

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The bridge pickup settles into its new home.

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Wiring the neck pickup is a little easier as the control route extends to the neck pickup cavity route. With the wiring done and everything temporarily in place, a quick sonic check is performed with my Massive Marshall Full Stack.

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The J-Bass is reassembled and ready for re-stringing.

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If you look closely, the brand name on the pickup covers can be seen. Pickup height is approximately same value as was used to install the original pickups, but our Jazz Cat already has his #1 Phillips screw driver ready and will set the ‘just right’ height by ear.

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Fender Vibro Champ Combo Amp ‘Almost’ Lost to Hurricane Harvey

Texas Amplification, operated by the late Darryl Shifflett, built some of the finest Fender Blackface clones available. Much of the inventory of Texas Amplification was subjected to the flood waters of Hurricane Harvey. This newly-completed combo amp was high enough to escape immersion, but did not escape the subsequent rain, humidity and condensation. Could the Unbrokenstring Crew make this new unit like-new again for its new owner?

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The nickel plated feet and corner hardware are new, but a light coating of rust from the screws has leached onto the hardware. The Tolex covering appears to be unaffected by the water.

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Here’s a close-up of the rust. Not a big deal, but this triggers my OCDC (like obsessive-compulsive disease with a bit of AC/DC tossed into the mix.)

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The back panels of the amp are held on with the Correct screws, but they are showing signs of iron rust as well.

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This back panel is plywood. It had been wet but had been slowly drying out and was no longer warped. Surprisingly, the Tolex covering was still glued in place.

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This bit of Tolex covering, however, had become unglued.

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The Jensen loudspeaker was high and dry, but we’ll check it for any damage.

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The loudspeaker is more-easily inspected by removing the baffle board.

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With the baffle board out, it’s easy to verify that everything is in good shape.

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More importantly, no apparent water damage had occurred here! The Unbrokenstring Crew is fairly certain that this amplifier was at least partially submerged at the height of the flooding. This loudspeaker and grille cloth appear unaffected!

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Rust Biox is a tool of the museum curator. When old objects are carefully cleaned and restored for display in a museum, such as old weapons or other artifacts, Rust Biox slowly removes iron rust while preserving the un-oxidized material under the rust. This was once sold in the United States as an automotive rust remover, but did not become a ‘hit’ and was removed from the market. The Unbrokenstring Crew, however, is just cool enough to have a source.

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After each item is processed with Rust Biox, a water rinse and hot air dry prepares it for re-use.

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The feet of the unit are nickel-plated steel over a rubber bushing. Here, the bushing is separated from the metal foot for processing.

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These screws hold the feet onto the bottom of the amplifier cabinet.

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The metal feet are restored. Next, the Rust Biox will remove the rust stains from the rubber feet.

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Interestingly, this line may have been the ‘high water mark’ and so this unit could have been partially submerged. Furniture polish will clean and condition the Tolex covering to like-new condition.

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Heat from the hot air pencil softens the Tolex adhesive. The hot Tolex is pressed into place and allowed to cool.

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The hot air pencil has done the trick! This cabinet appears to have never been wet.

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The electronics are brand new, with no signs of water damage or corrosion.

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The Fender Vibro Champ is a single-ended Class A design, a low-parts-count, simple-to-build amplifier with surprising response and tone.

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All magnetics used in Texas Amplification products are procured through Mercury Magnetics. Top-of-the-line!

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The violet jewel in the pilot light tells us that we are ready for business!

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All back together, this amp is running a four-hour-long burn-in to verify that it is 100%. …And dry out anything still wet. This unit was delivered to its new owner, who promptly placed it in his recording studio.

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Squire Jagmaster Gets a Total Make-over And Then Some! Part Four of Four

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!

Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626