This 1968 Epiphone Al Caiola Standard came stocked with P-90s and a 5-switch Tone Expressor system.
Photo courtesy of Guitar Point (guitarpoint.de)
Hello and welcome back to Mod Garage. Not long ago, I came home late from a band rehearsal, still overly excited about the new songs we played. I got myself a coffee (I know, it's a crazy procedure to calm down) and turned on the TV. I ended up with an old Bonanza episode from the ’60s, the mother of all Western TV series. Hearing the theme after a long time instantly reminded me of the great Al Caiola, who is the prolific session guitarist who plays on the song. With him in mind, I looked up the ’60s Epiphone “Al Caiola” model and decided I want to talk about the Epiphone/Gibson Tone Expressor system that was used in this guitar.
The Epiphone Al Caiola model was built in the Gibson Kalamazoo factory and was similar to an Epiphone Sheraton, with a longer 25 1/2" scale. It was built from late 1963 until 1969 and was available with different pickups like Gibson mini-humbuckers and P-90s. The guitar would be renamed the Al Caiola Custom to make way for the Al Caiola Standard that was introduced in 1966, but both models had the Tone Expressor system.
The guitar has a Telecaster-like wiring configuration: two pickups, master volume and master tone, 2-way pickup-selector switch. Since the circuit only has a 2-way switch instead of a 3-way switch, you can’t play both the neck and bridge pickup at the same time. (Maybe Al Caiola didn’t like a middle-position sound; who knows?) There are also five additional mini-slider switches labeled 1—5 which make up the Tone Expressor system.
“With the individual slider switches of the Tone Expressor system, you can combine all five switching positions in any way you like, so you have countless possible combinations.”
Having a look under the hood reveals the Gibson Varitone system used on the ES models. My first thought was this was new wine in old bottles, but after having a deeper look, there are differences between the standard Gibson Varitone and the Tone Expressor system. The Gibson Varitone uses a 1.5 H inductor, while the Tone Expressor system has a 15 H inductor on board. The Varitone is a rotary switch, so you can only dial in one of the switching positions, no combinations. With the individual slider switches of the Tone Expressor system, you can combine all five switching positions in any way you like, so you have countless possible combinations. Electronically, the Tone Expressor is a switchable band-rejection filter; mids are attenuated and the result is a crisp, more twangy tone.
In this first of two parts about this very special circuit, I want to describe the switching positions of the Tone Expressor system. First, here are the individual parts:
• 500k audio master volume and master tone pot with a 0.02 μF tone cap. This configuration will work with mini-humbuckers as well as P-90 pickups.
• 2-way pickup-selector slider switch. Having the possibility to engage both pickups together (no matter if in parallel or in series) would enhance this wiring noticeably.
• 15 H inductor (choke). The inductor in this circuit creates a series of notch filters together with the caps of the individual switches, so the circuit doesn’t remove all signal above a certain frequency, but only a certain amount above and below that frequency. There is a lot of debate about using an inductor or not, and if so, what type.
Personally, I think adding an inductor is not the best choice. The design may have worked at the time, but today, most of us are looking for different sounds. While the Varitone has its fans, it was never very popular because it can suck tone, and a lot of people say that it doesn’t have a major effect anyway.
If you want to use an inductor and find a matching one, these have center-tapped primaries and secondaries. Use the entire primary or the entire secondary, and ignore center taps for the Varitone wiring. I had the chance to measure several original inductors (labeled TF-90-1C), and they all showed something between 12 H and 17 H; keeping their tolerances in mind, you can use any inductor in this ballpark.
• 10 M resistors. There is a 10 M resistor connected to the circuit in series to each of the five caps. These “pull-down” resistors prevent loud popping noises when using one of the switches—standard when switching capacitance like on the Varitone system.
• 100k resistor. Together with the caps on the switches, the single 100k series resistor creates a frequency selective voltage divider, which is essential to create a proper frequency notch. The value is well-chosen so there is no need to replace it.
On the Varitone rotary switch, position No. 1 is the bypass mode. The Al Caiola, with its slider switches, naturally doesn’t need an extra switch for this. When no switch is engaged, the Tone Expressor system is in bypass mode. In general, we can say that the bigger the cap, the thinner the tone, and vice versa. Or in other words: The bigger the cap, the more the humbucker tone is tidied up towards a more twangy and single-coil-like tone.
An up-close look at the controls for the Tone Expressor system.
Photo courtesy of Guitar Point (guitarpoint.de)
Here is what each switching position does:
• Switch No. 1 with 1000 pF cap corresponds to position two of the Varitone rotary switch and has a very subtle effect. It’s an unmistakably PAF-style humbucker tone, but with the bass frequencies tidied up a little. This setting can help cut through a mix and will prevent a boomy, woolly tone when playing full-tilt.
• Switch No. 2 with 3000 pF cap corresponds to position three of the Varitone rotary switch and is my favorite setting. Still a PAF-style humbucker tone, but tighter and with more transparency. This tone never gets too boomy and rides on the edge of the P-90 territory.
• Switch No. 3 with 0.01 μF cap corresponds to position four of the Varitone rotary switch. This reminds me of a typical P-90 tone with a tight bass and clarity in the high frequencies—very cool for some break-up blues playing.
• Switch No. 4 with 0.03 μF cap corresponds to position five of the Varitone rotary switch and is a very twangy and single-coil like setting that sounds like a Stratocaster—very useful and versatile.
• Switch No. 5 with 0.22 μF cap corresponds to position six of the Varitone rotary switch and is the most twangy setting. It reminds me a lot of a good Telecaster, especially with the bridge pickup.
Next month, we will look into different ways to set up and mod this circuit, so stay tuned!
Until then ... keep on modding!
Pickup screws with latex tubing.
Here is a step-by-step guide on how to eliminate most of these issues. And if you haven’t faced such problems on your Tele, you can still give these a try, and chances are good that you never will. These procedures will not alter the tone of your Telecaster in any way, so it’s better to have it and not need rather than to need it and not have it.
Checking the Pickups
Over the years, I have seen the wildest things coming stock from the factory, especially on budget pickups: unbent metal tabs on neck pickups, loose metal base plates on bridge pickups, bridge pickups only held by the springs, and other crazy stuff.
Let’s start with the neck pickup. Make sure the cover is installed tightly and is not loose in any way. The metal cover is only held by three metal tabs that are bent around the bottom of the pickup, one of them usually connected to the pickup’s ground. Make sure they are tight, holding the metal cover firmly in place. If not, they need to be re-bent. Be careful to not break them.
“Often, these small metal springs can cause feedback, and I’m sure Leo Fender had his reasons for choosing latex tubing instead.”
On the bridge pickup, the metal base plate on the bottom needs to be attached firmly. Check with your fingers to see if it can move. If so, even in only one spot, you need to re-glue it to isolate vibration. Otherwise, it will squeal at high volumes. This is easy to do, and the easiest and best way is to completely take the base plate off, clean it, and re-glue it with a thin layer of silicone from your local Home Depot.
While you are in there, it’s always a good idea to convert both pickups to 3-conductor wiring by breaking the ground connection of the metal cover (neck pickup) and the base plate (bridge pickup). Attach a third wire to one of the lugs of the metal cover and another one to the metal base plate, and solder both to a grounding point of your choice, e.g. the casing of one of the pots. This can be helpful for future mods, like any 4-way switch mod, where this is a mandatory requirem
Un-springing the Pickup Attachment
If your pickups are attached with metal springs to enable height-adjustment, you should replace them with some latex tubing. Often, these small metal springs can cause feedback, and I’m sure Leo Fender had his reasons for choosing latex tubing instead of metal springs. This is cheap, fast, and easy to do; you can get latex tubing from any guitar store or online for only a few cents. (See photo at top.)
Cushioning the Pickups
On a Tele, there’s usually a gap between the bottom of the pickups and the inside of the guitar’s body. This open space can exacerbate feedback issues. Luckily, it’s easy to solve with a piece of foam.
Using a piece of white paper, outline the routing for each pickup. Cut them out as a template for the foam. Then, trim the foam to shape. Place the foam on the bottom of both pickup routings, and you are done. There is no need to glue or attach the foam in any way.
It’s important that the bottom of the pickup is touching the foam so there is no more open gap. I usually use foam that is a little bit thicker than necessary, so the pickup will press on it slightly, making a perfect connection. The type of foam is not important as long as the gap is closed. I prefer to use foam rubber that is easily available in a variety of thicknesses.
Closing Support Routings
On a lot of Telecasters, you can find open support routings from the neck pickup routing towards the electronic compartment. This is for easier access when running the wires of the neck pickup through the body.
Note the various cavities in this typical Telecaster body.
Photo courtesy of Singlecoil (https://singlecoil.com)
There are two ways of routing the wires of the neck pickup through the body: from the neck pickup routing directly into the electronic compartment or into the routing of the bridge pickup, and from there into the electronic compartment, which is the traditional way. In the latter case, make sure all the wires are running underneath the additional piece of foam. If you have any open support routings on your Telecaster body, put some foam in to close them. You don’t need to attach the foam; the pickguard will hold it in place. The kind of foam doesn’t matter, and you can also use things like a small piece of cotton cloth, cotton wool, Styrofoam, etc. in there.
Addressing Bridge Plate Flaws
One of the most common reasons for unwanted feedback is the typical Telecaster bridge plate. The Telecaster bridge system was designed in the ’40s by Leo Fender himself and is crude at best. Its function was simply positioning the strings and providing a rough, easy adjustment of the intonation and the string-height settings. It wasn’t long before Fender released the much-improved bridge design found on the Stratocaster.
The current production Fender vintage bridge plate, as well as most budget aftermarket bridge plates, is made from thin hot-rolled steel in a deep-drawn process. Using this manufacturing process, parts can be made very quickly and cheaply, but at severe cost in quality. The steel used must be very soft and thin to allow it to fold and bend in the corners.
A classic Telcaster bridge plate.
Photo courtesy of Singlecoil (https://singlecoil.com)
Unfortunately, this process creates unusual internal stress in the steel, which can bow the plate so it can’t sit flat on the wooden body. This is a common reason for unwanted feedback on so many Teles. Interestingly, the early vintage bridge plates Fender made used a cold-rolled steel procedure to relieve stress in the material and to avoid this problem. Long live modern mass production!
If you have a Tele with a bowed bridge plate, there are three possible things you can do:
• Change the bowed bridge plate for a straight and even one. (This is the easiest way to avoid any troubles.) There are excellent replacement bridge plates on the market, so you’ll have plenty of choices for materials, designs, finishes, etc.
• Get the bowed bridge plate to a metal fabricator or tool maker so they can try to solve the problem for you. This process will probably cost you more than a new bridge, so this is only an option if it’s a special bridge you want to keep, no matter the cost.
• Drill two small additional holes on the front of the bridge plate, shown as red dots in the picture. After re-installing the bridge plate on the guitar, tightly drill two wood screws through these holes. Often, modern replacement bridges already have these two additional holes. In many cases, this will do the trick, so you don´t have to buy a new bridge.
If you have gone through this entire list and still have problems with feedback, it’s very likely that the pickup itself needs to be re-potted, which a pickup builder can do for you.
Next month, we will stay on the Telecaster subject, taking a close look at the famous Andy Summers Telecaster wiring, so stay tuned!
Until then ... keep on modding!
