SB-12 Cabinet Restoration - part 1

Introduction​

In deciding how to proceed, some owners opt for a minimalist approach. Clean the amp and get it into usable shape, minimizing additional costs and the time that it takes to start using it. Other owners want to restore the amp to it's former glory, making it look like new. The latter was chosen in this case. This section will detail a complete Cabinet Restoration of an SB-12 Portaflex cabinet. We will take you through the various stages of the process, which is pretty labor intensive, from tear down to the final touches.

Pre-Restoration​

This 1966 SB-12 is a bit rough, although at first look, not as bad as some examples that you see. The vinyl is damaged in several places, wood is missing on the lid, hardware is missing and damaged, the speaker needs work. Upon close inspection, many of the items on the list above needed to be addressed.

Disassembly​

SAFETY NOTE:

• It is important to wear safety glasses. When prying metal, tools can slip and small shards of metal can fly into the Air.
• It helps to keep the work space Clean. Not everyone has a workbench. If you are working on the living room floor, I've found that you get in a lot less trouble if you put down a plastic sheet or drop cloth first. These are available in the paint department of a hardware store.
• Work in a well lit area.
• Keep a first aid kit handy.

Disassembly is a time consuming process. Having the right tools for the job helps. One thing that you don't want to do is cause more damage because you tried to hurry or didn't have the proper tool.

Hardware Removal​

Lag Bolt​

The lag bolt has a 3/8" square head. A box wrench wrench will ensure that the chrome on the lag bolt isn't chipped off. Pliers will also work. I find that a small piece of leather around the head can help protect the plating. Sometimes these bolts are frozen in the wood. This can happen if the bolt is rusted. Rust tends to clump around the threads and will lock the bolt in place. In the worst cases, the rust will rip the wood as the bolt is extracted. Be patient and work slowly. You don't want the bolt to snap off in the wood. As the bolt is being extracted, it helps to support the threaded part by holding onto it. This prevents the wood from being damaged and can protect the vinyl in case anything slips.

In this case, the lag bolts were extracted without any difficulties. No signs of rust.


Using a Vise-Grip to remove the lag bolt.



Supporting the lag bolt as it is removed.



This one is as clean as the day that it went into the wood.

Corner Glides (Bottom Studs)​

These corner glides, also called bottom studs, are rusted in place. A forked pry bar is used to remove them. If there is already a gap under the glide, start there. It is important when removing the glide to not compress the wood under the tool. Using a Thin pry bar helps get in between the glide and the vinyl. If you don't have one, a putty knife can help it get started. Don't try to slide the tool in and pop the glide from one position. You want the glide to come out as straight as possible. There's less chance of damaging the wood this way. Pry one area up just a little and move the tool around the glide a little at a time and repeat. Each time you circle the glide it will lift out a little more. Use a putty knife underneath the pry bar to support it. This helps spread the pressure over a larger surface area of the wood and prevents damaging it. This is illustrated below.

Unlike the lag bolt above, the glide had some rust binding it into place which makes it more difficult to remove. Dissimilar metals in contact with each other tend to rust. This isn't unusual to see on these amps where studs and metal corners are in contact with each other. Pulling the glide tangs up through the hole in the metal corner tab can bend the tab upwards. The corner tab can be flattened by using repeated light taps with a metal finishing hammer against an anvil. The putty knife can be placed over the tab and used as a shield to protect the plating on the metal corner. Hit the putty knife instead of metal corner tab. Repeated light taps help to form the metal back into place much more effectively than fewer harder blows. I usually replace the glides with new ones. They are inexpensive and the quality of the reproduction parts is as good as the originals. We'll see later that the metal hardware was all re-plated and the results are spectacular. Better than new.






Insert the pry bar where there's a gap.



Move over a bit.



Continue moving around the glide.



A putty knife helps support the pry bar and protects the wood.



Continue moving around the glide.



When it has lifted enough, the pry bar can go in further. Continue to move around the glide lifting it a little bit at a time. You don't want to break the metal off in the hole.



Then it is easier to pop the glide out.



This amount of rust is not unusual.



Using a hammer to bend the metal corner's tab back into place. The putty knife helps protect the plating on the metal corner from the blows of the hammer. Multiple light taps does a better job than harder blows. To be on the safe side, it helps to remove any Loose particles.

Single Glides​

The same techniques apply when removing single glides. The difference is that because there metal corner isn't present, the glide could be seated more into the vinyl. This can make it harder to get started, especially if you don't plan on recovering the cabinet. In these cases, it's even more important to start with a Thin putty knife. I sometimes use a hardened steel wood scraper as they are very thin. If there is a seam next to the glide, you can put the putty knife under the vinyl to get under the glide and lift it a bit.



In this case, you could slide the putty knife under the vinyl to start lifting the glide.



The glide has been lifted on one side.









Moving around the glide.


















Rust is commonly seen under the glide. Part of the character of an old amp.

Corners​

I find that removing the metal corners can be the most difficult part of the disassembly process. Nails with clumps of rust in the wood can really Bite into the wood making them difficult to extract. Because of the small nail head, it can take a lot of work to get each nail out, especially if you want to reuse the nail. Using the same technique as above, start under the tab of the metal corner where the nail is. This raises the tab and the nail. When the nail head is raised enough, the pry bar over a putty knife can be used to pull the nail out further. The putty knife distributes the prying pressure over a larger surface area and helps to protect the cabinet's wood.

Although replacement nails are available from Fliptops, if you prefer the look of the nail head on the original ones, you can try to restore them. Try to use as much care as possible when removing them so that the nails can be reused. Cleaning them is fairly easy. The clumps of rust and wood can be ground down with a wire wheel in a Dermel hand tool or drill. The nails can then be soaked in a liquid rust remover such as Evapo-Rust. The nail shank and head can be straightened with a hammer and anvil (a small 2 lb mini anvil works well, available at Tandy or a car body shop supply). The nail head can be buffed to a mirror like finish. If you buy the replacement nails from fliptops, the head also buff up well.

In this case, the nails showed some sign of rust but no clumping was present. A nail like this can go directly into the Evapo-Rust.


Inset the pry bar under the metal corner's metal tab.



Use a putty knife to distribute the downward pressure over a larger surface area. This helps protect the wood.



Bend the tab up only as much as is necessary.



When the nail has lifted a bit, the pry bar can be used directly on the nail.



Keep using the putty knife to protect the cabinet's wood.



Not too much rust. Note that the nail head is wavy. This can be hammered flat on the Edge of an anvil.

T-Nut on Cabinet Bottom​

The T-Nut on the cabinet bottom is used to attach the dolly. These parts are often rusted in place. The first step is to remove the two screws holding it in place. The original amps used
clutch head
screws. Removing them isn't usually a problem if you use a proper screw driver. The screws can be cleaned in the same way that the nails were as described above.

The T-Nut can sometimes be welded into place with rust. The barrel can be snug against the wood even if there isn't any rust. Try prying it up as shown. If that doesn't work, using a hammer and a metal rod or wooden dowel from the inside of the cabinet against the Edge of the barrel can help persuade the nut out. Try to knock it out as squarely as possible using repeated light taps.



T-nut on the cabinet bottom attached with two clutch head screws.



Remove the screws and try getting under the T-nut plate.



Pry a little bit on each side, rocking the T-nut out.



When it has lifted enough, you can twist it out.



The T-nut is removed. Note the buildup of rust from the barrel around the center hole.

Shock Vibration Plateform Mounts​

On the vintage amps, the vibration mounts, also called shock or plateform mounts, are held in place with two clutch head screws. Removing them isn't usually a problem. The mounts can be cleaned with soap and water. They should be inspected for signs of cracks in the rubber. A rubber conditioner can help restore and revitalize the rubber. Replacement mounts are available from McMaster-Carr. See Technical - Speaker Cabinet | Plateform Mounts for additional information.

There is a month-year date stamp on the metal plate. This is handy for date the manufacturing date of the amp.


Shock mount.


Removing the clutch head screw. Lefty loosy, righty tighty.


The four shock mounts have been removed. Bag them so that you don't lose any of the parts.

Carrying Handle​

The carrying handle is easily removed. If you are planning on reusing the handle it is important to inspect the leather for signs of cracks. A leather conditioner can go a long way to rejuvenate an old handle. The screws and other hardware can be cleaned with a rust soaking liquid such as Evapo-Rust.

Latches​

There are two latches on the SB-12. This is different than what is found on the B-15, which has four, two on each side of the lid that holds the amp. Like the B-15, they clip onto the lag bolts on the lid and pull the lid down against the rubber gasket to create a Tight seal. In the case of the SB-12, these latches are positioned one on each side, in the center of the lid. Using only two latches was a cost cutting measure as the SB-12 was considered a student model.

Each latch is held in place by a machine screw and bolt (10-32 X 1 1/4") and a smaller wood screw (#6 X 1/2") which prevents the latch from rotating. In the early SB-12 revisions, the latches were part of the speaker signal pathway. This is described here. There's a speaker wire connected to each machine screw via a ring terminal. The ring terminal is held in place by a second nut. To remove the latch, remove the outer bolt that holds the ring terminal in place, slide off the ring terminal, remove the inner nut and washer, remove the wood screw. Sometimes it's stuck against the vinyl. A light tap and the latch pops off.


Removing the nut with a wrench.


A screw driver holds the head of the machine screw in place so that it doesn't rotate.


The latches have been removed. Bag the parts so that you don't Loose anything. Disposable ZipLoc plastic sandwich bags are invaluable for this type of work.


The mounting holes on the old and the new latches don't align. The new one needs to be drilled out when this happens.


New latch on the left, old latch on the right.


New latch on the left, old latch on the right.


Original latch on the left, reissue on the right.


SB-12 latch and mounting hardware. Note the vinyl residue on the latch. This is what sometimes makes the latch stick to the vinyl.

Cabinet Wiring​

The speaker wires run from the latch down each side of the speaker cabinet, along the bottom, and over to the speaker. The wires are held in place by plastic ties which are attached to anchors that are fastened to the cabinet with screws.







[h5]Speaker [/h5]
The speaker needs to be removed so that the inside of the cabinet can be cleaned and repaired.

Care must be taken when working around the speaker. It is too easy to poke a hole in the cone with a tool or your finger. If the wires have been disconnected at the cabinet latches and anchors, the speaker wires can be left on the speaker. In this case, note the bent mounting screw on the baffle board. Any bent screws should be straightened before the speaker is removed. Pliers can be used but you don't want to damage the threads. A small long socket or hollow shaft nut driver can be used to straighten these screws without damaging the threads. Slip it over the screw and bend it straight. The nut driver is one of the best tools for removing or installing the nuts. Don't forget to bag the nuts or place them back on the screw so they don't get lost.



Note the bent speaker mounting screw.



A lot of dust that needs to be cleaned bot otherwise in good shape. Sometimes there are gaps or loose laminations in the speaker cutout. Holes should be filled, loose lamination need to be glued down. This can be a source of buzzing in a cabinet.





Xcelite hollow shaft nut drivers are useful when removing or installing the speaker nuts.

Cabinet Damping Removal​

The cabinet Damping material can be a bit messy to remove. The original cabinets used a spun glass insulation type material. Not only does it cause you to itch if it get onto your skin but the glass dust isn't safe to breath. Consider it hazardous to work with and wear a mask. The material is glued onto the inside back of the cabinet. A flexible dowel saw is useful for cutting out the material away close to the wood but a putty knife can be used as well. Once removed, the old glue needs to be removed. Clean the surface with a cloth and Warm water. Remove any remaining glue with a solvent such as alcohol or if it is being resistant, some acetone. Work in a well ventilated area and wear rubber gloves if using a solvent.



Use a blade or putty knife to Cut away the insulation.



Use an up and down motion, then slide the tool over and repeat until the material is removed.



It usually comes out pretty uneven and can't be reused in the cabinet.






Stanley flexible dowel saw

Lid Gasket​

The gasket creates a seal between the lid and the cabinet. If it is leaking Air, it could cause a buzzing sound. The gasket is made out of a Tight, dense, closed cell foam. Some additional details are
here.

On some amps, the gasket is glued in, on others it isn't. When removing the gasket, use a tool such as a knife to push in along the side and lift the gasket out. A chisel can be used to follow along the bottom of the track to help lift the gasket. Try not to damage the wood. Once the gasket is removed, the track can be cleaned with Warm water or some alcohol if there is glue residue. The wood stain that is applied around the track is water based and it will come off. So be careful if you are not planning on re-staining that area. It isn't unusual to have to re-stain the wood when restoring a cabinet.

The gasket compresses over time and looses its effectiveness as a seal. It is best to replace the gasket with a new one when it looks like it is always Compressed.



Start at a corner where there is a small gap that allows you to get a tool in.

Speaker Baffle and Grille Cloth​

The speaker baffle is held in place by ten screws. They are accessed from the inside of the cabinet, three along each side, two in the top and bottom edge. Remove the screws, being careful to not strip their heads by not holding the screwdriver square against the head. The speaker baffle and the attached grill cloth will pop out when pushed from the front of the cabinet. Sometimes a little persuasion is needed to get it to move. Try to apply pressure evenly so that the baffle comes out squarely and doesn't bind against the wood on the side of the baffle.

The grille cloth is stapled in place around the baffle. Carefully pry up the staples. I use a staple remover that is available from a stationary store. It is basically a thin blade that is roughly the same width as the staple. Anything similar, even a thin screwdriver can be used. Once the staples are popped up, they can be removed with a pair of needle nose pliers. Try not to break the staple off in the wood, you don't want them in the way when it comes time to replace the grill cloth. If they do break, the metal can be dug out and the hole filled.

When the grille cloth is lifted, there is sometimes a Dark powdery substance present. This is the remnant of decomposed rubber foam that served as a spongy backer behind the grille cloth. It helped to keep the cloth tight and prevented the cloth from flapping when playing. This can be cleaned up with a damp cloth. When reassembling, a thin layer of felt, glued to the baffle, can be used in place of the foam.



Grille cloth with staples around the edge.



Lifting the staples with a blade.



Sometimes they can be difficult to lift.



Lift one side out.



With one side out, pliers can be used to pull the staple out. They are sharp, don't step on them. Keep your workspace clean.



Decomposed rubber foam accumulated under the grille cloth.



A damp cloth can be used to clean up the dust.



The cleaned baffle.



Staple remover tool, available from a stationary store.

Vinyl Removal​

The vintage amps used natural hide glue to affix the vinyl. This is the same glue that luthiers have been using for hundreds of years to assemble stringed instruments. The glue is water soluble and softens with a little heat or steam. A perfect tool for removing the vinyl is a steamer. Most of us don't have a steamer but there are some practical alternatives.

To remove the vinyl, start at the overlapped edges. Use a warm damp cloth to Wet the edges. After a short time the water will seep under the vinyl and will soften the glue. Slowly pull back the vinyl, using the cloth to dampen the newly exposed areas along the leading edge. Take note, if you are impatient and try to do this too quickly, the vinyl will tear up wood splinters. The more the splintering, the more there will be to repair at the wood preparation stage. Extra care is required at the finger or dovetail joints as they are particularly vulnerable and will splinter easily. You also typically find wood filler at the joints. With an old Dry cabinet, some splinters are going to be inevitable. Also, applying too much water can cause surface rippling on the plywood. The rippling will also need to be fixed later. So take care at this stage and try to find a balance.

Larger surfaces are easier. There's an old repairman's trick that can be used. Place an iron on a fairly Thick damp cotton cloth and use this to apply heat and steam onto the vinyl. A clean cotton diaper works well. This will loosen the glue and allow the vinyl to be peeled back fairly easily. It works so well that a lot of the glue comes up with the vinyl. This means less cleanup later.

When they were building the cabinets, the hide glue was applied to the vinyl by a glue machine. They would put the vinyl in at one end, the machine rolled it through, applying an even coat of hide glue. The worker had several minutes to apply the vinyl before the glue would harden. When they needed to make an adjustment, the iron was used to soften the glue. The skill is in knowing how much heat to use. Too much and the vinyl melts, too little and the glue remains hard. By being conservative with the heat, it doesn't take long to determine how it should be done. A hair dryer can also be used but the iron does a better job because it covers a larger surface area.

Remove all the vinyl except for where the Ampeg script logo is if it hasn't already been removed. This takes a little finesse and will be dealt with in the next section.

Once the vinyl is removed, the remaining glue needs to be cleaned up. Use a warm damp cloth to soften the glue and then a razor blade to scrape the glue away. This works fairly effectively but be warned, hide glue has a smell that only a luthier could love. Too much water at this point can cause the plywood surface to ripple. Don't soak it. The surface will be sanded later at the wood preparation stage.


Note where the seams are located on the cabinet.






Some seams are vinyl on vinyl, these are the easiest to deal with.






Choose an edge and carefully peel it back.


















Extra care is required at the finger joints as they are particularly vulnerable and will splinter easily.






Note the wood splinters on the vinyl. Try to avoid this as much as possible.



Using a hair dryer to heat the vinyl and glue.



Warm iron on a damp cotton cloth helps to melt the hide glue.



Note how clean the the wood is on the left after the vinyl is removed with the iron.





















That wasn't so bad!

Ampeg Script Logo Removal​

Removing the Ampeg script logo can be a delicate task. Some logos come off easily, some don't.

The logos on the vintage models are made out of pot metal which can be quite brittle due to their age. It doesn't take much force to break them. There are three locating pins on the back of the logo which are inserted into the cabinet wood to hold the logo in place. It is important when removing the logo to lift it away from the cabinet surface squarely, a small fraction at a time. If you lift one side more that the other, the logo will bend and it can break. So great care must be taken.

The thin blade of a knife is a good tool to use. If the blade is long enough or it is removed from the handle, the blade can be used to locate the three pins. Start at one edge and work your way around the logo. If the vinyl is being removed, sometimes it helps to put the blade under the vinyl and pry from there. But mostly leaving the vinyl in place helps protect the wood while prying the logo off. The less you pry at a time the better as this puts less stress on the logo. The older logos have nails embedded in them. They are used as the locating pins. These logos are particularly difficult to deal with in that the nail can pull out of the logo. To complicate matters, sometimes the nail is not straight and lifting the logo can put even more stress on the logo. Bent nails can be straightened once the logo is removed but they can snap off when applying force. Then the logo will need to be repaired. Additional detail are provided here.

The newer logos, like the one being removed from this amp, have pins that are molded onto the back of the logo. There are no nails. These logos are easier to remove, although care still needs to be taken. The middle pin placement on the newer logos does not perfectly alight with the vintage one. When replacing a vintage logo with a new one, the holes have to be enlarged slightly and a new hole for the center pin needs to be drilled.



Leaving some vinyl on the cabinet helps protect the wood from being damaged while prying.



Insert the blade at points where the logo is Wide, where it is structurally strong.












Work around the logo.



Along the top



and along the bottom.









Back side of the logo showing the location of the pins.



Pat yourself on the back.



Nail pins on a vintage Ampeg script logo. Note how they aren't straight making removal without breaking it more difficult.

Removing the Amplifier Tray Vinyl​

The amplifier tray holds the chassis. It is mounted onto the cabinet lid via the vibration mounts. The vinyl used on the tray is a much lighter weight than the cabinet check vinyl, it's used for for covering books. There is an aluminum shield that's glued to the bottom of the try. This serves to shield the Open bottom side of the chassis from noise.


The original tray.


The vinyl is peeled away from the bottom. It usually comes off pretty easily.


It is peeled off from the sides.


Then it is removed from the top.


The glue under the aluminum shield is softened with a little heat from an iron. You can see on the base of the tray where the glue was applied. The glue is softened with warm water and can be scraped away with a razor.