Peavey

Peavey Bandit Combo Amp Refurb

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David found this fine old Peavey combo amp in a pawn shop for almost next to nothing. Could the Unbrokenstring Crew resurrect it?
This saga begins on a cool Saturday morning in the Guitar Center Pasadena parking lot.  If you look closely, you can see right through this unit.  Literally.  What are we getting ourselves into this time?

 

Electrically, this unit is mute.  No sound comes from it.  But, as the story is told, this amp languished in the barn for years so we have to expect the worst.

 

Name, rank, and serial number, please.

 

This part number goes to a Peavey Spider loudspeaker.  This is gonna be fun, as you shall soon see!

 

The grille is off.  This poor thing is a mess.

 

If a rat gets hungry enough, it will eat anything.

 

Perhaps it was not tasty enough, as the rats left plenty of bits of uneaten loudspeaker cone behind.

 

The brunt of the rat nasty-ness was taken by the reverb tank cover.  We need to clean this up right away!

 

The spring reverb tank is in perfect condition.

 

The tank cover did its job and kept this reverb tank in a pristine condition.

 

Pledge furniture polish contains solvents and emulsifiers that are excellent for cleaning Tolex.

 

The nice lemon-y scent is just the thing to counteract the barn smell.

 

The bottom of the unit is a mess, though.

 

The amplifier electronics are on the bench.  The unit is upside down.  The reverb tank connector is to the left.

 

The bottom cover comes off.  We need to go over this unit with a close eye for damage due to humidity and dust.

 

Perhaps moisture (rat urine? mouse-ture?) has seeped under the solder mask and attacked the copper on the circuit board.  Everything gets a bath.

 

The top side of the electronics is pretty filthy, as we might expect.

 

The circuit board is free of the chassis.  Everything is being scrubbed with water, alcohol, and compressed air.  The switches, jacks, and controls are cleaned, flushed, and lubricated.

 

Tracing signals, this guy is bad.  This IC is replaced from stock.

 

I want to clean up around the cases of the transistors.  The heat sink is at zero volts while the transistor case is at +70 volts or so.  The dirt may bridge across the insulator.  Not on my watch!

 

These power transistors are just fine.  They are also super-rare.  Luckily, I won’t have to replace these.

 

But they sure do clean up good!

 

The transistor on the left is already installed.

 

We use Wakefield heat sink grease on power devices at the Unbrokenstring Shop.  Old Skool.

 

The original mica insulator is reused.

 

This is actually quite messy, but is a thing of beauty when I do it.

 

Both sides of the washer are coated with compound.

 

The whole stack is installed as shown.

 

While we are here, some of the solder joints could use some attention.

 

This amp is now delivering 75 watts into 8 ohms.  This chassis is Good To Go!

 

Back in the case it goes.

 

These jacks are on the rear of the unit.

 

The knobs press on.

 

This guy goes in the trash.  Wait?  Aren’t we going to recone it?

 

No.  We don’t have to recone.  Peavey Spiders are available without the magnet.  No tricky alignment issues here!

 

When the magnet was removed from the old loudspeaker, the magnetic gap was cleaned and then sealed shut with tape.

 

Once the old magnet is aligned, three screws hold it in place.  We’re done!

 

This is the new loudspeaker, seen from the front.

 

A rear view shows us the cleaned cabinet and reverb tank cover.

 

The loudspeaker looks new, because it is new.

 

The grille was cleaned up and is seen here, reinstalled.

 

The refurbed chassis slides in from the rear.

 

These washers go underneath the trim plates thru which the chassis screws extend.  Don’t leave these out!

 

These big trim pieces are metal, coated black.

 

And these, boys and girls, are how the chassis is suspended inside the cabinet.

 

Installing this trim piece is all that is left to do.

 

David is really tickled with his like-new Peavey Bandit!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

 

Peavey 1810 Bass Enclosure Crossover Doesn’t (Crossover)

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Most of what you see in this post works well. However, a crossover network inside the speaker cabinet doesn’t work at all. Could the Unbrokenstring Crew sort out a solution that would put this cabinet back to work?
Here is some file old hardware from the 1980s.  This cabinet has an eighteen inch subwoofer underneath two ten inch loudspeakers.

 

Behind this panel is found a crossover network that routes the input signal to the proper destinations.  The crossover automatically routes the really low frequency stuff to the 18 inch loudspeaker and the rest is routed to the ten inch loudspeakers.  Or, you can specify which signal goes to which driver using the BI-AMP jacks.

 

The sheet metal screws hold this circuit board in place.  An inductor plugs into the pins in the center of the picture.

 

The input jacks are seen in this view.  The capacitor is part of the crossover network, and has been replaced.  As this is in a high powered audio network, the electrolytic capacitor is a non-polarized variety.

 

We can examine the circuit side of the printed circuit board to figure out the schematic for this assembly.

 

This inductor is cooked.  Unfortunately, this part is no longer available.

 

An examination of the inductor may give us some clues that we could possibly use to fix it and use it again.

 

This component can take the place of three different inductors, thus the three wires.  Any two wires yield a different inductance.  Unfortunately, the insulation is thoroughly cooked.  No salvaging this guy.

 

The functions of each ‘net’ on this circuit board is labelled with a felt tip marker.

 

For this particular model of crossover, the inductor wires we need to use are indicated by this inductor symbol.

 

This is an inexpensive crossover kit, with similar specifications.  We can harvest this inductor for use in the crossover.

 

Here are a few details, listed on the end of the box.

 

This inductor is has a laminated bar core.

 

We can remove this inductor from the circuit board and use it in the Peavey circuit.

 

The back side of the donor network is covered with some self-adhesive foam rubber.

 

The foam sticks really well!  But now we have access to the solder joints that need to be unsoldered.

 

The mechanical mounting scheme is VERY robust for this heavy part.  We can use all of this in the Peavey circuit.

 

These white plastic caps are handy to hold the mounting nut and to insulate the exposed iron core.

 

We will use the original circuit board as a template for finding and marking places to drill new mounting holes in the Peavey circuit board.  We can search around for a practical mounting location.

 

The mounting holes are marked.  Away We Go!

 

One end of the inductor is electrically wired here.

 

The other end of the inductor is wired here.

 

We will make lock the threads of the mounting screws with this stuff.

 

The thread locking compound is thin enough to seep into the threaded fasteners and lock them.

 

Now, we can reassemble the crossover network assembly.

 

The original inductor was mounted in the foreground.  This doesn’t look to tacky, does it?

 

One last look before it disappears into the enclosure.

 

The panel is ready for reassembly into the enclosure.

 

No.  Wait.  We need a new gasket between the I/O panel and the cabinet enclosure.  This self-adhesive foam strip material is just the ticket for this application.  Note the mitered corners.  Because I’m OCD like that.

 

Holes for the mounting screws are cleared with the Exacto knife.

 

OK, NOW is one last look at this assembly.  The wire pairs go to the loudspeakers in the cabinet.

 

This system is pretty awesome.  Everything tests out at full power.  Life Is Good!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

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

Peavey Stereo Chorus 212 Head Stuck In Mono

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The owner of this amp was so anxious to get it fixed, he removed the chassis from this Peavey Stereo Chorus 212 combo and even helped load it!  The amp plays, but only one stereo channel is operational.  Can the Unbrokenstring Crew help?

A quick look of the front panel shows the inputs and the normal (clean) channel controls.

Did you catch the missing knob?  The Unbrokenstring Crew will find a replacement, which is no small thing because these are no longer available new and are only available from spares or salvaged from a non-working unit.

This amp uses a digital signal processing (DSP) module to make all this audio magic.

Interestingly, the DSP module creates two unique audio signals (stereo) from a single mono input.

The ground lift switch is on the front panel, which is a nice touch from many other designs.

This dual OPAMP is non-functional.  However, this is not the root cause of the missing stereo signal.

This is the DSP module in this amplifier.  We have only one audio stream as an output from this device.

A piece of cardboard serves an an insulator so that the bottom of the DSP assembly can be probed.

Here is where the DSP processor outputs both audio as a stream of ONEs and ZEROs.  We are OK here!

This chip processes the two DSP streams in a manner similar to a successive approximation analog-to-digital converter.

The bit streams are split using an analog switch.  Here is the output of the switch assigned to the working channel.

And this is the output of the switch on the non-working channel.  Time to change the switch!

Desoldering today is performed with a traditional iron, rosin flux, and copper braid.  This keeps solder balls to a minimum.

The circuit board is cleared of excess solder and flux.

The new MUX chip is available through the usual sources.

With the tweezers, the new MUX chip is oriented properly on the circuit board pads.  See the tweezers?

After soldering, the workmanship is inspected with this hand-held microscope.  The high-powered white illuminator is on the left, and the black cylinder next to the big IC chips is the optical microscope itself.

Any remaining solder flux is removed with alcohol.  The rag gives the dissolved mess somewhere to go.

Both channels are operating at full power.  The knob is coming from an eBay auction.  When it gets here this head is ready to return to the eager customer!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Peavey Citation MK IV Two Channel Guitar Amp Head Repair

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Rod had this Peavey head kicking around and thought it was time to put it to good use. However, it didn’t work at all. Could the Unbrokenstring Crew work its magic and bring this road warrior back to life?
A quick scan of the front panel shows that the input circuit sports the sort of flexibility that the Peavey Marketing Department loves to explain to anyone who would listen…
Each channel has independent gain, and a master volume to Rule Them All.  Effects can be inserted via the front panel.
On the rear panel, we have parallel speaker jacks and the usual ground/no-ground power switching.  Peavey often married different front panels, which contained preamp circuitry, to different rear panels, which carried power and audio amplifier components.  The ‘series’ number goes with the power amp, not the front panel.  We Got This.
Name, rank, and serial number, please.
Pulling the front panel, we see that all of the components are mounted on one circuit board.
I took a few pictures to be sure that the wiring and cables were returned to the same spot when we are through.
The cable to the right is just wired to the power indicator.  The other two carry signals.
This is a better view (to be sure that they cables are properly oriented on their pins.
The front panel is free of the rest of the unit.
All of the controls and switches will be cleaned so this assembly comes completely apart.
We can now clean and lubricate everything now.

 

Can you spot the broken solder joints?
Someone has been here before!  This needs to be cleaned up, too.
The Blue Shower is a good cleaner.  The DeoxIt contains a lubricant for the potentiometers.  Good Stuff!
Back Together it all goes!
This screw hole was stripped out.  First, we will soak the stripped hole in the wood with this wood hardener.
Next, a birch dowel is cut to partially fill the hole.  The dowel reduces the apparent diameter, allowing the screw to hold.
With the stripped hole repaired, we are back in business!
This unit plays very well, and all the controls and switches are Like New!

 

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626