refurbish

Peavey Artist Combo Amp Refurb

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This Peavey Artist combo amp was WAY too distorted to suit even the most extreme metal head. Could the Unbrokenstring Crew look into this and put this unit back into service?
First, a tour.  You can have two channels, or a mix of the two ‘Automix’ inputs.  This was a ‘thing’ back in the day.

 

The other controls are straight-forward.

 

The standby switch is in the front, whereas the AC power on is in the back.  Actually, I like this because if both power switches are in the back, half the time I switch the wrong one.

 

The AC line duties are all squared away on this side.  The City Of Los Angeles has their own version of UL.  That’s the yellow and red sticker.

 

The right hand side of the rear chassis has the ins and outs for this amp.

 

These are all Peavey-branded tubes.  They are all in good shape and will stay in this amp for now.

 

So we put a clean sine wave in, and this is what we get out.  The positive power supply is weak.

 

An overall gut shot shows power on the left, preamp on the right, and power amp on the bottom.

 

These capacitors have begun to swell and push the seals outwards.

 

We have signs of overheating.  These resistors handle power distribution and are somehow related to our problems.

 

The other power supply has a cooked resistor as well.

 

Here I am just documenting all the plugs and wires so I can get them back in the same place.

 

These capacitors are also bulging and will be replaced.

 

Time to remove the power supply board and work it over.

 

This circuit board holds the tube sockets.  We have an intermittent short to ground under this assembly.

 

At first I thought that the short was under the tip terminals of these jacks, but that was not the case.

 

I am going to pull this assembly out and look it over as well.  The blue, red, and brown wires are high voltage.

 

The blue capacitor in the upper right is the ‘death cap.’  If it shorts, 115vac is connected to the chassis.  Not good if you ever touch the amplifier.  Fatal if you touch the amplifier with one hand and grab a microphone with the other hand.

 

This circuit board is supported by the tube sockets.  All four sockets will be unsoldered.

 

Out this guy comes.

 

Here is our short circuit.  These are component leads from parts installed on top of the circuit board and soldered from the top.  I guess if the excess length is out of sight, then it is out of mind.

 

Here are some of the parts on the top side.  I don’t think these were replaced in the field, but rather it came from the factory with the untrimmed leads.  Sloppy.

 

However, wires that are too long are easier to deal with than wires that are too short.

 

I am cleaning up the bits of crap in the bottom of the chassis, using some sticky tape as a way to capture the crap.

 

I have installed new bleeder resistors and new capacitors on this assembly.  That big blue resistor is a high voltage dropping resistor.  This part is fine and will not be replaced.  However, those are not made anymore, and I have some of the last remaining stock of the OEM resistor.  You’re welcome.

 

Everything gets trimmed and cleaned up before reassembly.

 

The power supply board has new caps everywhere.

 

The Ty-Wrap was my idea.  These big parts need some mechanical support, but I’m not big on lots of hot glue.

 

The original power resistors were way out of spec, so these new parts are higher wattage to take the abuse.

 

These caps on the preamp board were replaced.

 

As was this guy.

 

These were the overheated resistors that we saw earlier.

These new resistors are actually more robust than the parts they replaced.  And they are flame-proof.

 

We are back on the air!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Crate Vintage Club 50 Amp Repair

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St. Louis Music produced this handsome tube-based Crate amp. Robin said that this unit is ready for some service.

I just love the blonde Tolex and clean appearance of this unit!

The front panel reveals that this is a single input, two channel unit.  The clean channel sports conventional treble and bass controls.  Bringing the effects loop to the front panel is a nice touch!  This jack is stereo, for in/out with one jack.

The gain channel has separate gain and volume controls, and a mid-tone control.

The foot switch is wired in parallel with the channel select switch seen above.  Note the separate controls for reverb for each channel!

These loudspeakers are original and still in great shape.

Taking a tour of the bottom of the chassis, this unit has an attached line cord.  The power transformer is affixed at an angle, as seen on the left.  The grey wires go to and from the reverb tank.

Five minutes of visual inspection is worth thirty minutes of troubleshooting.  Can you see the problem?

To remove the chassis, we need to unsolder the cables to the reverb tank.  I marked this one so that it can be reinstalled in the proper place on the circuit board.
The loudspeakers are wired in parallel.  This pic documents the wiring colors.

The chassis is now free of the cabinet.  A quad of EL84 tubes serve as the class AB push-pull output circuit.

The preamp tubes, in the foreground, and all 12AX7s.

Removing the brackets on the output tubes is a little gnarly, though.  This screw will be replaced.

Silicone foam cushions the envelope of the tube from  the stresses of vibration and thermal expansion.

To do any soldering on the main circuit board, all the controls need to be disassembled.  Marshall knobs, anyone?

We have three jacks to disassemble in order to liberate the electronics.

The primary and secondary wiring is easily disconnected from the circuit board, as shown here.

One more chance: Do you see any electrical issues?

We have the main circuit board well in hand.

Some glue was used to support the large mechanical parts.  This stuff needs to be chipped away.

Here, we are checking the caps in-circuit with the Heathkit capacitance checker, just to verify that they are toast.

My only criticism of this amp (and others) is that the tube sockets are directly attached to the circuit board.  The thermal expansion is more than the average solder joint can stand.  Wire those sockets by hand; don’t mount on a PCB!

Here we are with new capacitors.  All of the solder joints have been inspected and reworked as required.

With the unit disassembled, this is a good time to clean up and polish that gorgeous front panel.

The wrong sized fuse was installed.  The Unbrokenstring has a complete stock of fuses, for such a moment as this.

Remember the broken screw?  Here, we are drilling and tapping the chassis for a new screw.

The blue masking tape was deployed on the inside of the chassis to catch all the metal shavings.

The screw fix worked!  As we knew it would.

The reverb tank wires are fished back through the hole in the chassis and refastened.

Everything has been reinstalled and we are ready to test.

This cover conceals the bottom of the amplifier chassis.  The amp was a little noisy.  Could some shielding help?

Aluminum foil tape is added to the cover.  This will be electrically in contact with the chassis of the amplifier.

Aluminum shielding goodness at its finest!  This is all on the inside, so no one but you will ever know that it’s there.

This Crate is very versatile – the clean channel is almost hifi quality, while the gain channel is a vast territory of sonic goodness to explore.  And LOUD!  Pick one of these up if you find one.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Bugera V22 Infinium Combo Amp Repair

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This beautiful combo amp excels in all categories except one…  no audio out.  Could the Unbrokenstring Crew help?

Taking a walk-around, the rear panel tells us that this amp was built in Macao, PRC.

Good corporate branding…

The TRIODE/PENTODE switch is advertised as a ‘half-power/full-power’ switch.  The LEDs labelled “Tube Life Monitoring” light up when the fuse in the plate circuit open, due to an internal short in the tubes.

Looking down from the end shows a handsome front panel with the Very Cool chicken head knobs.

The top view of the chassis shows us another good instance of strong corporate branding. I do like the protective cage over the vacuum tubes.

Here we get a good look at the bottom of the main circuit board.  I am not a big fan of soldering tube sockets straight into a circuit board, but this seems to work here.

Most everything on this side of the circuit board appears to be OK.

I was documenting the location and orientation of these cables, in case we needed to further disassemble the unit.

These solder joints appear to be cold.  We have found our intermittent ‘no sound’ cause!

Every other solder joint is removed, fluxed, then resoldered.

Ah, that’s better!

Ironic that just a couple of cold solder joints would bring this wonderful combo amp to its knees. This guy is 100% now!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Wireless Shure SM58 Battery Leaked

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This microphone was part of the estate of an amateur journalist. As she moved into treatment and into hospice, there were other concerns besides removing the batteries from unused equipment. Could the Unbrokenstring Crew revive this unit and make it usable again?

This microphone is a basic SM58 capsule coupled to a battery-operated VHF FM transmitter.

These are often seen in many performance venues as well as in worship, news-gathering, and business settings.

 

The 9v battery has leaked.  We will need to disassemble the unit to clean up the mess.

 

These VHF units are on frequency allocations that are shared with other services and may be subject to interference.  However, these units work well if you are fortunate enough to be in a part of the country where interference is low.

 

The microphone capsule is built into the head of the microphone, which unscrews from the electronics.  Connections between the capsule and the electronics are reliable regardless of how many turns are necessary to tighten the threaded bodies together.

 

The gold fingers touch those rings seen in the previous picture.

 

This inside snap ring keeps the electronics inside the housing.

 

Before we remove the electronics,we need to get the switch actuators out of the case.  The cover removes easily enough.

 

The switch actuators come straight out.

 

This is looking good!

 

This is the complete analog FM transmitter.

 

Working with the battery contacts is much easier now that the case is out of the way.

 

Reassembly is the reverse of disassembly.  Wow, that’s profound…

 

These big tweezers are all I need to get the inside snap ring back in place.

 

Reassembled, the new battery is installed and we have a green light!

 

The receiver indicates that an FM carrier is present.

 

We have an intermittent problem with audio out of the microphone.  We need to look at the capsule.

 

I guess we’ve screwed the pooch by now.

 

The wires are cracked where they emerge from the solder joints.  These will be reworked.

 

This brass adapter goes between the capsule and the rest of the housing.

 

We are back together again!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Professional Advice for Those Caring For Flood-Damaged Guitars

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Roy Bowen and Scott Leedy of RS Guitarworks in Winchester, Kentucky had it in their hearts to reach out to Houston area musicians, documenting their experiences gained while working with flood-damaged guitars during the big flood in Nashville back in 2010.  The Unbrokenstring Crew is honored and blessed to be able to publish this document for your edification.  This supplements my previous post, which was general in nature and included electronics.  To wit:

 

Guitar Flood Triage

Below is a list of steps that we developed while restoring guitars from the Nashville flood and Hurricane Sandy.  The following steps should be taken as soon as possible.

 

  • First remove strings.

 

  • If truss rod is not removable, loosen truss rod ½ turn, add a couple of drops of penetrating oil on the threads then tighten ¼ turn.  On vintage Fender or Gibson guitars where the truss rod can be removed, remove truss rod lug. Oil the threads then re-install snug but not tight.  You want to make sure threads are lubed so the truss rod does not rust in place.

 

  • Remove all parts from body including hardware and electronics.  Wood will try to move and solid items like screws & tuners will not let it move.  This can cause cracking of the wood, as well as cause rust staining in the wood.

 

  • On bolt on instruments remove the neck.

 

  • Take all hardware and place it in bags filled with uncooked rice and leave it until you are ready to re-assemble.

 

  • All electronic parts such as pots and switches should be cleaned with a quality electronics cleaner and then stored in uncooked rice as well.

 

  • Air-drying of the wood is best after parts have been hand dried inside and out.  Keeping guitars in a small room with a dehumidifier can also help.

 

  • Do not try to use any cleaners on the finish or hardware of the guitar until it is properly dried and stabilized.

 

  • Do not try to tape down loose binding or wood coming un-glued as it may damage fragile finish loosened by water

 

  • Get the guitar to a qualified repairman as soon as possible.

 

Be sure to visit http://www.rsguitarworks.net to tell them THANKS and to check out their restoration work with other water-damaged guitars.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626