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Classic Amps: The 1950s Gibson GA-40 Les Paul Amp

Dave Hunter
|
08.06.2009


A tweed 1959 GA-40 on top of two mid-’60s examples

In the early days of the electric guitar, manufacturers who made both guitars and amps very often attempted to sell them as matched sets—and players very often bought them that way, until they figured out there was nothing wrong with mixing and matching to suit your varying tastes in each. Throughout the mid to late1950s, Gibson’s flagship solidbody electric, the Les Paul, was partnered with an amp that has become a classic in its own right: the GA-40 Les Paul Amp. While, of course, this combo hasn’t attained values anywhere near those of the guitar it was designed to sell with, this sleeper of a tone machine has recently become far more appreciated by players and collectors alike, and recognized for the unique and inspiring piece of amp design that it is.

Surprisingly, the GA-40 wasn’t Gibson’s most powerful amp of the time, contrary to the kind of firepower that you might think the powerful Les Paul Standard demanded. But remember, the Les Paul wasn’t designed to be the blues-rock and heavy-rock monster that it would prove itself to be in the mid ’60s and beyond. It was originally designed as a solidbody alternative for jazz and pop players, guitarists much like its namesake, and for this market, Gibson deemed a pair of lower-powered 6V6 output tubes and a conservative 14 to 16-watt rating absolutely adequate. Don’t believe for one second, however, that this diminutive rating means a GA-40 can’t roar when you want it to: these are real fire breathers, truly scorching when you crank them up, and a lot louder, too, than that output rating might imply.

GA-40s with two-tone covering made between 1956 and ’59 are generally the most desirable, because they also house the preferred circuit and tube configuration for this model. Part of what’s so groovy about this amp is that it is nothing like any of the Fender designs from the same era that have become such classics. The Gibson brand has been relegated to the darker corners of amp collecting, but throughout the ’50s and early ’60s the company really was trying to cut its own path, offering bold designs and impressive workmanship, and unwilling to follow the lead of any other maker, no matter how popular those “youngsters’” amps might be proving! As such, the GA-40’s circuit is very different from any of the classic tube-amp templates that are more familiar today in so many repro, reissue, and “boutique” amplifiers (other than one… mentioned below).


Inside the chassis of a 1956 GA-40

Much of the GA-40’s excitement revolves around the unusual preamp tubes used in each of its two channels. This is a rather unusual “pentode” preamp tube—meaning it has five functional elements other than the three of the standard 12AX7 dual-triode—called a 5879. Something of a cousin of the EF86 pentode preamp tube familiar from early Vox AC30 and AC15 amps, and sometimes used by newer makers such as Matchless, Dr Z, 65 Amps and others, the 5879 sounds nothing like the familiar 12AX7, and has a higher gain and a fatter, thicker overall tone. This higher gain doesn’t necessarily mean that this tube itself distorts more easily, but rather that it pushes a firm, bold signal onto the next stage, where you can definitely kick the whole shooting match into distortion if you want to.

The fun factor is multiplied by the fact that each of the GA-40’s two channels was voiced differently, Channel 1 (designated Instrument/Microphone) being noticeably hotter than Channel Two (designated Instrument). Using an A/B/Y pedal to switch between them (or to use both together) offers a useful instant lead-boost from Ch1, or you can patch them together (by plugging into Input 1 of Ch1 and running a jumper cable from Input 2 to Input 1 of Ch2, or vice versa) to blend the two voices together all the time. Channel 2, the Instrument channel, has its own little treat in store in the form of one of the most delectable tremolo circuits available. Powered by a single 6SQ7 preamp tube, the GA-40’s tremolo is deep, thick and lush, and provides anything from a throbbing, swampy wobble to a machine-gun staccato.


The control panel for a 1956 GA-40

Both channels share a single Tone control, but even that is very different than the simple, single-knob Tone controls in so many amps of the era. The GA-40’s Tone control is located in the output stage of the amp, between the phase inverter and the output tubes, rather than immediately following the volume controls like most. It serves to subtly tweak the high-end content of the sound, following a “less is more” philosophy that leaves the GA-40 sounding rich and full-throated at just about any setting. All of this tonal goodness was pumped through a single Jensen P12Q 12-inch speaker. It’s a classic in its own right, but some contemporary owners of these amps prefer to replace it with a modern, more efficient speaker—especially if they are going to be gigging the amp on a regular basis—in order to protect the Jensen for posterity, while also getting a little more oomph out of the amp. That said, the original P12Qs, when in good condition, break up beautifully for blues and vintage rock and roll. Now that this model is definitely in the spotlight, good original GA-40s are becoming hard to find, and expensive when you do find them. Gibson has never offered a precise reproduction of the model, but the Victoria Amp Company does manufacture an amp called the Electro King, which is very faithful to the original circuit, complete with dual 5879 preamp tubes and 6SQ7-powered tremolo circuit.

Amps courtesy of Nate Riverhorse Nakadate
Photo Credit: Kerry Beyer

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