5E3 Coupling Cap Mod

Written by
Logan Tabor
Published on
January 22, 2021 10:56:37 AM PST January 22, 2021 10:56:37 AM PSTnd, January 22, 2021 10:56:37 AM PST
Welcome back fellow DIYers! Today, we want to go over a mod for our 5E3 Tweed Deluxe Style Amplifier kit.  This mod is simple, quick, cheap, AND it will brighten up your amp's sound.  But first, let's talk about why someone would want to implement this modification...

While the 5E3 circuit is an absolute classic which definitely dishes out some killer tone, a lot of players find that this circuit is inherently dark in tonality.  I myself have even noticed that I have to turn the tone control almost all the way up to get a bright enough sound to satisfy my eardrums. What's wrong with turning the tone control up all the way and dialing the sound in that way? When you turn the tone control all the way up, you are essentially giving the amp EVERYTHING the tone stack has to offer; all the frequencies completely unchecked.  This can (and pretty much always does) introduce undesirable noise into the signal, since all of the higher/noisier frequencies are "wide open." So in order to pull some of the inherent low end out of the amp's sound without having to crank the tone control and hear all that noise, we need to make a change! Listen below to hear my 5E3 before the mod. This is with my tone control straight up between 6 and 7, and my volume on 4. The first pass is on the bright channel, the second pass is on the normal channel...


But don't worry, this is one of the easiest and least risky mods one can make to the 5E3.  All we have to do is replace two of our .1uF coupling caps with .022uF coupling caps instead.  No big deal!  Alright here's a list of everything you'll need to pull this off:

Soldering Iron
Solder
Needle-nose Pliers
(2) .022uF Orange Drop Capacitors
Alligator Clips
Mojotone Chassis Stand  (Optional)
Digital Multimeter
Wire Cutters

Okay now before we dive in, it's important to make sure we've drained our filter caps. This is something we always practice just to be certain we don't get seriously harmed in the event of a mistake! If you're unfamiliar with this process, please read below for instructions on how to do drain your filter caps.  If you know this process and are confident in the safety of your chassis, please skip ahead to step 2...


STEP 1 : DRAINING FILTER CAPS

Once our chassis has been removed from our amp and laid out on our work bench, we will need to drain the filter caps.  To do this, you'll need to use your alligator clips to make a ground connection between the metal chassis and the resistor indicated in Images 1A and 2A below (make sure the amplifier is turned off for this procedure)...





Once you've made this connection, pull out your multimeter, turn it to DC Volts and apply one probe to the metal chassis, and another to the positive lead of the last filter cap, as seen in Image 3A below...



In the above image, you'll notice that my caps haven't fully drained all of their voltage. That is as low as I could get them by creating a voltage drop in this part of the circuit. When you see that your caps will no longer drain past a certain voltage, you'll remove your multimeter probes and disconnect your alligator clips from the above noted points on the circuit board. Next, you'll connect one end of the alligator clips to the metal chassis and the other end directly to the anode (or positive side) of the filter caps (see Image 4A below)...



Then return your multimeter probes to their original position (one on the metal chassis and one on the positive lead of the filter cap). You should see the remainder of the voltage drain; once your voltage is gone, your amp is safe to work on!


STEP 2 : REMOVE THE OLD COUPLING CAPS

Now we need to pull out the old .1uF coupling caps; these caps are shown in Images 5A and 6A below...





Grab your needle-noise pliers, heat one of the solder joints (one cap at a time), and when the solder is soft enough, use the pliers to remove the capacitor's lead from the old joint (Image 7A)...



After you've successfully removed the old .1uF caps, grab both of your new .022uF caps, bend their leads at roughly the appropriate length for them to fit into the existing solder joints in the circuit board (Image 8A)...



Having our caps stand off the board just a little bit (once mounted) is fine, but we don't want them standing too far off so grab your wire cutters and trim a little off the bent ends.


STEP 3 : INSTALL THE NEW COUPLING CAPS

Yep, we're already here.  To install the new caps, all we have to do is heat the old solder joints and press the leads of our new caps into them.  This may require the use of some additional solder, but you can address that on a case-by-case basis.  You can either use your pliers or your hands to hold the cap in place while the solder cools.  This is all about preference of course, but just as a note it is always safer to not stick ones hands into the chassis!  Once you've installed these new caps you should have something along the lines of Image 9A below...



And wouldn't you know it...that's the mod! Easy, cheap, quick. All there is to do now is plug it in and hear the difference. You're always welcome to test voltages before plugging the amp back in, but I'm confident that I didn't mess anything up in there so I'm going to connect my amp to the speaker cabinet and just listen to hear if there are any audible issues.  When I hear no obvious issue, I'll reinstall my chassis properly and jam out like a maniac.  Okay here are sound clips AFTER the mod.  Same amp settings as before, and the first pass is bright channel, second pass is normal...


I am immediately happy with the results, as I've been looking for a generally brighter tone.  Both channels are what I would consider more useful and more versatile.  I've always loved this 5E3; it's an absolute classic and it never fails on me.  But I'm glad to have made this mod and allowed it to breathe a little more.  That concludes this week's Fix It Friday, we hope you enjoyed it. See you next time!