A local shop got it to pass signal and technically function, but with four power tubes, some big-bruiser transformers, and a rating of 105 watts, I was expecting more.
A well-worn U1040 out of its cabinet.
The U1040’s back panel includes jacks for both reverb and tremolo footswitches.
It’s probably a lingering artifact from some emotional turbulence years ago, but I’m fond of the goofy, early-’70s, two-tone blue Univox amps with the orange logos. I bought a weary, nonworking U1040 project off Craigslist and have been trying to nurse it back to health. A local shop got it to pass signal and technically function, but with four power tubes, some big-bruiser transformers, and a rating of 105 watts, I was expecting more. The amp’s volume seems weak and muted, its tone is nothing special, and the whole thing just seems sonically constipated. I’ve been told this amp has an unusual design. What remedy might the amp doctor prescribe for this lackluster combo?
Although I’ve never owned one, I absolutely remember these cool and unusual-looking amps. According to the Univox site, your 1040 Quad Reverb was one of a large contingent of models designed and marketed in 1971. Although Univox was originally a Japanese company, around the time your 1040 was produced, these amps would have probably been assembled in Westbury, New York, using Japanese-built chassis. This model was also available with a 4x10 speaker configuration (U1044). These amps sold for $480 at the time, which was a pretty decent chunk of change considering that a Volkswagen Beetle was selling for under $2,000.
Although this 1040 model exists, apparently its schematic does not—at least online. So as a reference, I chose a schematic for another model with the same basic specs, the 2-channel 1010. It has 10 tubes, a solid-state power supply, reverb, tremolo, presence, and a 105-watt RMS output. My guess is this will be almost identical to your model.
When troubleshooting older amps with no known history, it makes sense to start with the tubes. Used or abused output tubes can certainly leave an amp with lackluster performance. Install another set of 6L6s and see if this makes a substantial difference. If so, have the new tubes biased properly for optimal performance. I’d also substitute each preamp tube and listen for an improvement. This may be a case where each tube replacement brings the amp another step towards proper performance.
While there are a few atypical design elements, there’s really nothing too “unusual” about it. The most noticeable difference is that the unit uses a 6AN8 triode/pentode tube in the reverb circuit. The pentode half of this tube feeds the triode half, which is basically a 12AU7, and the triode side drives the reverb tank. A little out of the ordinary, but certainly not an area that should be causing amp anemia. The following design differences, however, could be possible suspects.
The power supply differs from what’s normally found in the majority of guitar amps. In most guitar amplifiers, the power-supply voltages that are fed to different stages of the amplifier are all derived, in one way or another, from the main supply voltage, traditionally called B+. But in this design, the power supply is actually split into two discrete sections. The full power supply (650V DC) is feeding the plates of the output tubes, while the rest of the amplifier is fed with exactly one half of that voltage (325V DC), which is sourced at the center of the power-supply filter stack.
Most Music Man amps used a very similar design, but since the preamp stages of the Music Man were all solid-state, the half power-supply voltage was only used to supply the screen grid voltage to the output tubes, and here is where a potential problem could exist in your amp. The half voltage is derived at the center point of two series capacitors. If these capacitors are worn, dried out, and out of balance, the half voltage could be substantially low and cause weak output from the output tubes, as well as lower gain in the preamp stages.
Check the half voltage. If it’s substantially low, replacing these two 100 μF 450V capacitors could bring the amp back to life. And while you’re at it, I’d replace all of the filter caps, as their performance could be questionable as well.
Next, I’d look at the output stage. In most designs, the plates of each pair of output tubes on either side of the output transformer are connected together. In this design however, the plates are separated by a 100 Ω resistor. If those resistors have failed, you may only be getting output from two of the four output tubes. Replacing those resistors should enable all four tubes to operate again.
If none of the above potential causes are the source of the lackluster performance, I’d finally suggest looking at the speakers. Over the years I’ve seen many instances where the original speakers in vintage amps can become weak and worn out, and the amp sounds and feels completely underwhelming. Disconnect the internal speakers and play the amp through a good extension cabinet. New speakers can make all the difference in the world.
Warning: All tube amplifiers contain lethal voltages. The most dangerous voltages are stored in electrolytic capacitors, even after the amp has been unplugged from the wall. Before you touch anything inside the amp chassis, it’s imperative that these capacitors are discharged. If you are unsure of this procedure, consult your local amp tech.
Jeff Bober is one of the godfathers of the low-wattage amp revolution, co-founded and was the principal designer for Budda Amplification. Jeff recently launched EAST Amplification, and he can be reached at firstname.lastname@example.org.
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Created in collaboration with legendary guitarist George Lynch of Dokken and Lynch Mob fame, the Mr.Scary Mod adds an adjustable tube gain stage and an onboard Deep control, which together are designed to enable an amp to have increased sustain while still retaining note definition and dynamics.
LegendaryTones, LLC today announced production availability of its new Mr. Scary Mod, a 100% pure tube module designed to instantly and easily expand the capabilities of many classic amplifiers with additional gain and tone shaping. Created in collaboration with legendary guitarist George Lynch of Dokken and Lynch Mob fame, the Mr.Scary Mod adds an adjustable tube gain stage and an onboard Deep control, which together are designed to enable an amp to have increased sustain while still retaining note definition and dynamics.
Originally released as the Lynch Mod in February 2021, the updated Mr. Scary Mod features the same core circuit as the Lynch Mod but is now equipped with a revised tube mix combo per George’s preference as well as a facelift in a newly redesigned electro-galvanized steel enclosure. As with the Lynch Mod, each run will be limited and the first run in Pumpkin Orange with Black hardware is limited to just 150 pieces worldwide.
The Mr. Scary Mod adds an adjustable tube gain stage on top of the cathode follower position, keeping note definition and articulation while further increasing sustain. Each Mr. Scary mod is meticulously built by hand in the USA, one at a time, and tuned using high-grade components. Equipped with a single ECC81 (12AT7) in the first position and ECC83 (12AX7) in the second, the Mr. Scary Mod can clean up beautifully when rolling down your guitar’s volume, and still adds scorching gain when you roll it back up. This is a gain stage that’s been tuned and approved by the ears of the maestro George Lynch himself.
“The Mr. Scary Mod excels with dynamics and is incredibly touch-responsive, allowing me to shift from playing clear, lightly compressed cleans to full-out aggressive sustain and distortion –and control it all simply by varying my guitar’s volume control and picking,” said GeorgeLynch. “In many ways, it’s an old-school approach, but it’s also so much more natural and expressive in addition to being musically fulfilling when you can play both the guitar and amp dynamically together this way.”
The Mr. Scary Mod installs in minutes, is safe and effective to use, and requires no special tools or re-biasing of the amplifier. Simply insert the module into the cathode follower preamp position of compatible amplifiers (includes Marshall 2203/2204/1959/1987 circuits) and
immediately get the benefit of enjoying a hot-rodded amp that delivers all the pure harmonic character that comes with an added pure tube gain stage. The handmade in the USA Mr. Scary Mod is now available to order for $319.
For more information, please visit legendarytones.com.
October Audio has miniaturized their NVMBR Gain pedal to create two mini versions of this beautifully organic-sounding circuit – including an always-on gain device.
The NVMBR Gain is a nonlinear amp that transitions gracefully from clean boost to overdriven tones. Volume increases from just over unity to about 10db before soft-clipping drive appears for another 5db of boost. Its extraordinary ease of use is matched by outstanding versatility: you can use it as a clean boost, push a stubborn amp into overdrive or create a just-breaking-up sound at any amp volume.
October Audio’s new family of mini NVMBR Gain pedals includes a switchable version that allows you to bypass the effect: one option features brand logo pedal graphics, while the other sports a fun “Witch Finger” graphic with a Davies knob as the“fingernail”.
The second version in the new lineup is an always-on device featuring the Witch Finger graphic and Davies knob, with the same NVMBR Gain circuit that lies at the core of the switchable version.
- Knob controls gain and clipping simultaneously
- Stunning silver hammertone finish
- Switchable versions are true-bypass, available with classic or witch finger graphics
- Authentic Davies knobs, including the “fingernail”
- 9V center negative power supply required
- Dimensions: 3.63 x 1.50 x 1.88 in
Witch Finger (always on NVMBR Gain) demo
All October Audio pedals are assembled in Richmond, VA, and available for purchase directly through the online shop. Street price is $109 for NVMBR Gain footswitch versions and $89 for the always-on device.
For more information, please visit octoberaudio.com.