Field Test: AmpRX Brown Box and P3 Line Tamer Voltage Regulators Reviewed

Modern power grids can put out a tremendous amount of voltage, and that is not something that always bodes well for tube amps.
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Modern power grids can put out a tremendous amount of voltage, and that is not something that always bodes well for tube amps. Vintage amps, as well as many modern hand-wired boutique models, are optimized to handle 117 volts maximum, and I’ve seen much higher readings coming out of the walls at studios and clubs around the country. Those extra volts can mess with your tone and lead to blown fuses and/or a trip to the repair shop. So what can you do to keep tube amps at a safe voltage? A Variac variable transformer is one possibility, but those things are heavy and can be easily misadjusted to deliver higher than normal voltages. Modern alternatives are available from Furman (—which makes a series of professional-grade power conditioners, including the very affordable AC-215A. You could also go with the two units on deck here: the AmpRX BrownBox and P3 Line Tamer, both of which are portable voltage regulators designed to keep your amp sounding great and electronically healthy.


The Brown Box ($349 street) is a two-knob device that allows the user to custom-tailor the amount of voltage that goes to their tube amplifiers for a host of tonal and technical benefits. The Primary Voltage Selector has settings for 120, 122, 124, and 128 volts, and is used to calibrate the Brown Box for the wall voltage being displayed in the backlit LCD screen (which also monitors amperage). Below that is a 5-position knob that adjusts the amount of voltage reduction: 0 (bypass), 3%, 4%, 6%, and 10%.

It’s this latter function that takes the BrownBox into a more technical realm, since, by monitoring the B+ voltage inside the amplifier with your DVM while using the BrownBox, you can fine-tune via the Reduction Level knob to obtain the correct operating voltage for a particular amp—a figure that could be considerably off spec (and potentially harmful to the amp) depending on line voltage anomalies. Even without going to this extra step, however, the BrownBox will enable you to correct for the line voltage in your area, with the benefits being better tone, longer tube life, and less breakdowns and repairs. I found this unit to be a no brainer to set up and very simple to navigate. Using it with my old Fender Bassman, the device increasingly rounded out the top end as I soaked the voltage down, while also giving a slightly saggier dynamic feel. This is a very useful aspect of the Brown Box, and one that separates it from standard power conditioners. Built in the U.S., the BrownBox features a custom wound 5-amp transformer and comes with a lifetime warranty.
Kudos Provides the ability to dial in the voltage needed to obtain exactly the tone and feel you’re looking for. Quality construction.
Concerns None.


The U.S.-made Line Tamer ($295 street) is a straightforward device with 6-volt and 12-volt reduction modes, dual AC outlets, a detachable IEC power cord, and a blue backlit LCD that is accurate within one volt. Housed in a sturdy, black powder-coated metal enclosure and further protected by a 3-year warranty, the box is rated for four amperes of continuous current, and features a Triad Magnetics transformer and a Carling toggle switch. P3 stresses that the most important reasons to use the Line Tamer are to protect the parts inside your vintage or boutique tube amp from high voltage and for the tonal benefits of using the correct power. Setup is simple: Connect the P3 to the wall outlet and plug your amp into one of the AC outlets on the opposite side of the housing. Turn the P3 on and observe the voltage reading on the display. If it’s more than 115 volts, use the appropriate setting of the Voltage Reduction switch to get it back in the range of 110 to 115 volts. From there, you’re ready to power up your amp with no fear of over-stressing the components. Paired with some of my vintage amps, including an Airline combo and a Fender Bassman, the Line Tamer cut down on some of the amps’ inherent noise and provided a very slight but noticeable smoothness across the frequency spectrum.
Kudos Streamlined design. Simple to use.
Concerns None.