Our resident Fender amp guru, Jens Mosbergvik, usually sings the praises of Fullerton’s classic offerings, but this time he switches sides to unpack his biggest gripes with the manufacturer’s legendary noisemakers.
Vintage Fender amps have a strong reputation among players in many genres. The brand is instantly associated with an endless list of great bands which created music that has stood the test of time. In terms of general tone, Fender’s original amplification strategy—which favors articulate, bright, transparent, and clean sounds—was a winning combination that myriad players still gravitate toward.
Through my previous columns in this magazine, I’ve shared the tips and tricks I’ve learned after playing, trading, and servicing old models from the California manufacturer. But today, it’s time for critical thinking. I’m switching sides to share the 10 most annoying things about vintage Fender amps. As usual, I will mostly refer to the black- and silver-panel amps.
“It breaks my heart that the original Deluxe Reverbs came with a weak and farty Oxford speaker, when it sounds so much better with a more punchy, clear-sounding C12N.”
Many of the critiques that I offer here ultimately advocate for simplification. All amp techs know that simple is good. Simple amps are lighter, smaller, cheaper, and have less things that can go wrong in the long run.
So, here is my list:
Two Jack Inputs
I’ve never met anyone who uses the second input. Back in the day, Fender thought we were going to swap guitars between songs without having to adjust the volume knob to compensate for the different pickups’ varied outputs. Wrong assumption.
Two Channels
I always use the reverb channel, even when using high distortion, at which point I simply turn the reverb down. Except for the Bassman, the normal channel is not needed at all. If all of the dual-channel amps were instead single-channel, like the Princeton Reverb, a lot of tubes and circuit components could be spared, leading to significant cost reduction and simplification of the production line. Even with the black- and silver-panel Bassman, I would prefer a single channel, as long as both the deep and bright switches were available. The only advantage with having a second preamp channel is the possibility to isolate the power amp section and the two preamp sections in diagnosis. But that still doesn’t make it worth it.
The Non-Reverb Amps
If I was Leo Fender, and I was looking to reduce costs, I would have trimmed my portfolio by eliminating the non-reverb Deluxe, Princeton, Vibrolux, and Pro amps. The rarer versions of these amps are no-frills, cool, and great value for the money. But there are reverb-equipped models that can do everything they do just as well and better. They’re not in as high demand, and they’re less profitable due to lower production numbers. Instead, I would have continued the Vibroverb after 1964, which would do the job as the only 1x15 combo amp in the portfolio. Just admit it: Everyone wants a Vibroverb.
Rectifiers
As another cost-cutting measure during my imaginary tenure as the founder of Fender, I would consider using a diode rectifier instead of a tube rectifier in all the bigger dual 6L6GC Fender amps. I like sag in tube amps, but I think very few players can really hear the difference between diode and tube rectifiers. Smaller amps intended for earlier breakup may have tube rectifiers, but they’re not essential there, either.
Glued and Stapled Baffles in Silver-Panel Amps
I wish Fender had continued the floating baffle in the early ’70s instead of the tightly glued and stapled-in baffles that are found in silver-panel amps post-1971. The screwed-in boards are much easier to repair and replace.
MDF Baffles
Medium-density fibreboard, or MDF, baffles are consistently the weakest point in Fender’s wooden cabinet construction, and eventually tear apart. I would much prefer a more dependable plywood pine baffle.
Small Output Transformers
These are found in both the Bandmaster head and the 1x15 Vibroverb—amps that deserve a firmer low end, and which should have the Super Reverb-class output transformer.
Lack of a Bright Switch
In my opinion, this is an essential EQ function that’s left off of Fender’s smaller amps, like the Princeton Reverb and Deluxe Reverb. Without it, these amps leave me no chance to enhance the details of fingerpicking on a clean tone setting.
Lack of Mid Control
This applies to many Fender amps. The bassy and flabby Pro Reverb would particularly benefit from a better mid EQ, with a much wider tone spectrum.
No Jensen C12N Speaker in Deluxe Reverbs
We all know how awesome the Jensens sound in the early black-panel amps, like the C10N in Princetons and Vibroluxes, the C10R in Supers, or the C12N in the Pros and Twins. It breaks my heart that the original Deluxe Reverbs came with a weak and farty Oxford speaker, when it sounds so much better with a more punchy, clear-sounding C12N.
So, there you have it: my list of 10 grievances with Fender. If you have more to add, please share your thoughts in our social media channels.
A close-up look at the author’s Fender Vibrolux, with a 12" Celestion Alnico Gold on the preamp side of the amp and a lighter, 10" neodymium Jensen Jet Series on the other.
How to expand classic Fender amp sounds with different speaker configurations.
As you know, replacing or augmenting the speakers of your Fender amps is the easiest way to organically change your guitar tone. So, let’s discuss some alternative speaker configurations for classic Fenders. We’ll also explore some basic knowledge about resistance, current, and power distribution along the way, which will enable you to safely experiment.
If you are replacing or adding speakers, it is important to verify that all speakers are in phase and that you wire the plus and minus terminals correctly. Otherwise, the speakers will cancel each other out and the result will be a thin, weird tone without much bass or character. This rule applies to all speakers in the main amp and in extension cabinets. For all the examples in this column, I will refer to 8-ohm speakers wired in parallel, if not explicitly mentioned otherwise. I will also use both the terms “impedance” and “resistance,” which are commonly used in these conversations, even though the correct term for speaker resistance is impedance. Got that?
Now, let’s use a Deluxe Reverb as an example. The most common trick to create a bigger tone and more spread from a Deluxe is adding a second cabinet with a 12" speaker. The Deluxe has just enough power to drive them both. However, I’ve found that the Deluxe’s 22 watts is not enough for adding a 15" speaker. The bottom end gets too loose and farty. For that option—which features a full clear bottom end and opens up the array of overtones—I would typically recommend a bigger, 35- to 40-watt amp. But there is an option for adding a 15" speaker to a lower-powered Deluxe. You can replace the 6V6s with 6L6GC tubes for more power. Then, adding a 15" speaker makes sense.
“It is important to verify that all speakers are in phase and that you wire the plus and minus terminals correctly.”
Here comes a few even-more-advanced tricks with the Deluxe Reverb. The first: Replace the original 1x12" baffle with a 2x10" baffle for snappier low-end response, more sparkle, and a more scooped tone. It is very easy to cut out a solid pine board and staple grille cloth onto it. With two 10" speakers, the total speaker impedance also changes from 8 to 4 ohms, and will suit the 6L6GC tubes better, since they have a lesser output impedance than the 6V6 tubes. After that mod, if I want to play at lower volumes, I unplug one speaker and use the Deluxe Reverb as a single 1x10".
An even more creative and rarer variant is to use both 10" speakers together with a 15". In this setup, you have to wire the two 10" speakers in series and connect the 15" via the external speaker output. The amp will then see two resistance branches in parallel:
- Branch 1: the two 10" speakers = 8 ohms + 8 ohms, for 16-ohms resistance.
- Branch 2: the single 15" speaker = 8-ohms resistance.
The current always wants to follow the path of least resistance, so the second branch with the 15" speaker will get twice the amount of power and current as the first branch. And since there are two speakers in the first branch, that total branch’s power is divided equally between them. This results in a roughly 67 percent + 17 percent + 17 percent power distribution for the three speakers. This is a healthy and good-sounding balance, since a 15" speaker requires and can take a lot more power than a relatively tiny 10" speaker. Be aware that you must not use the amp in this configuration without the 15" plugged in, or you will damage the power tubes. The amp expects a 4-to-8-ohm impedance with the 6L6GC tubes. The two 10" speakers alone at 16 ohms is too far outside the safe operating range.
I will also briefly mention a change-up for the 2x10" 35-watt Vibrolux Reverb. If you want more punch and a bigger low end from this model, you can replace one of the 10" speakers with a powerful and efficient 12". I have had great fun fitting a 12" Celestion Alnico Gold on the preamp side of the amp and a lighter, neodymium Jensen Jet Series Tornado 10" on the power transformer side of the amp, where there is less physical space for a big speaker magnet. You now have three power levels: the 10" alone, the 12" alone, or both together for maximum punch. I can even add another 12" external speaker cabinet via the external speaker output for a mega spread on big stages. If I want to add a 15" extension speaker, I prefer to disengage the internal 10" and use the 12" and the external 15" together. My favorite modern 15" is the Eminence Legend 1518. It is impressively responsive. Also, it balances nicely with a classic vintage black-panel Fender tone.
I hope these ideas and tricks inspire you to experiment with speakers.
Need more headroom or gain? Spin the bottles.
[Originally published: 9/2/2019]
You might guess from the title of this column that I love Fender amps. And you’d be right. From a musical and engineering perspective, I think vintage Fender blackface amps are the best ever made. With bright, American-style speakers, they deliver pure and natural tone. Their channels, with volume and EQ, are intuitive for any guitar, bass, or keyboard player. It’s impossible to not find a decent tone in less than 10 seconds. From a technical perspective, their handmade tube-based circuits are simple, and they were built with high-quality components. And today, there are easily available parts and schematics, and an abundance of other online technical information, which makes it possible for many techs and players—including you—to service these amps.
Classic Fender blackface amps have been an inspiration for an entire industry. They’ve appeared on countless stages and an incredible amount of great albums by legendary performers. Why? Mostly tone and clean headroom. So, for this debut column, let’s discuss what we can do to make those two factors work best for you via tubes.
Reverb and tremolo were the main functional innovations in Fender’s blackface line. The king of blackface amps, the Twin Reverb, produced 85 watts from four 6L6 tubes and had enormous power and output transformers, a non-sagging diode rectifier, and two powerful 12" speakers. The 4x10 dual-6L6 40-watt Super Reverb has half that power, a softer tube rectifier, and smaller transformers. Still, the massive array of four 10" speakers is screamingly loud and sometimes difficult to handle for its weight (65 pounds), size, and volume. A 4x10 is more directional and scooped in the low mids than a 2x12. So a guitar plugged into a Super Reverb can end up competing with the bass. Experience is required to tame these amps. Once you know how to handle them, you will be rewarded with an overwhelming and physical sonic experience.
In the blackface world, the 1x12, double-6V6 22-watt Deluxe Reverb’s advantage is that it’s small and light, at 42 pounds. It breaks up earlier than its bigger relatives due to the less powerful 6V6s, small transformers, and a small speaker cabinet. Additionally, the original Oxford 12K6-5 speaker farts out early and is very weak, although it also delivers a true signature vintage Fender sound. And who doesn’t want their amp to break up easily these days? I have kept the Oxfords in my Deluxe amps. Before the internet, few people knew they could replace the 6V6s with 6L6s and replace the Oxford to double the Deluxe’s volume.
The V6 12AT7 phase inverter tube can be replaced with a 12AX7 to reduce headroom in large 6L6 amps.
Via my website, fenderguru.com, I often get questions about how to achieve different tones in blackface amps run at lower volumes. The answer often lies in the tubes. So let me share some simple tube tricks that will help you develop an understanding of how tubes function—and how they can be used to affect changes—in the typical two-channel AB763 circuit in the Twin, Super Reverb, Vibroverb, Pro, Vibrolux, and Deluxe amps of the original blackface era.
The tubes in these circuits are typically identified as V1 through V10, looking at the back of the amp from right to left. Here are some tricks:
- The V1 12AX7 tube in an amp’s normal channel can be removed for more preamp gain and reduced headroom in the vibrato channel. It can also be replaced by weaker tubes, like 12AY7s or 5751s, for less volume/gain. I always pull out this V1 since I use the vibrato channel and want solid preamp gain, which the single V2 delivers.
- The V3 12AT7 reverb driver for the vibrato channel can be replaced with a 12AU7 for less reverb and improved reverb knob control.
- If you’re only using the normal channel, think about removing the V2 through V5 tubes for the vibrato channel. That will give you more gain and headroom in the normal channel. (FYI, the 12AX7 in the V5 position is the tremolo tube.)
- The V6 12AT7 phase inverter tube can be replaced with a 12AX7 to reduce headroom in large 6L6 amps.
- Several alternatives to 6L6 power tubes exist. I mostly use 6L6GCs. In a Twin Reverb, you can pull either the V7 and V10 or V8 and V9 tubes for half power and earlier breakup. Ideally, but not totally necessary, you should disengage one speaker to match the impedance change.
- In a blackface Deluxe, the GZ34 in the V9 slot is the rectifier tube. If I want reduced headroom and more sag, I use a 5U4GB.
And there you have it: You’re on your way to becoming a Fender guru, too!