Instruments (CMI)—the GA- 70 was formally
introduced in the 1956 full-line catalog. The
most immediately striking feature of the GA- 70
was its cabinet. It stood 22-1/2" wide by 20-
1/2" high and 10-1/2" deep. It had a brown-and-tan, buffalo-grained fabric covering and
a rectangular speaker opening that extended
from the bottom of the amp to the top and
was flanked by two solid panels. At the top of
the speaker opening, glued onto the woven
saran grille, was a brown bakelite badge with
the Gibson logo and a suede steer head. The
western theme continued on the control plate,
where a silk-screened lariat outlined the edge
of the chromed panel. Like other Gibson cabinets of the time, the front, sides, and bottom
were 1/2" solid wood, while the top panel was
of denser plywood. Robert Chwaliszewski of
Buffalo Amplifiers has both restored and built
replicas of dozens of ’50s Gibson amps, and
he believes the GA- 70 cabinet contributed
directly to the tone of the amp. “The shape
of the cabinet, the panels on the front, the
height, the materials—all those things gave the
GA- 70 a unique tone and a lot more oomph
out of that Jensen.”
The first series GA- 70 was called “Country
and Western” in the 1956 catalog, and it was
almost a direct clone of the 1955 Fender Pro.
The tube complement consisted of two 6L6s
in the power section; a 12AU7, a 12AY7, and
a 7025 in the preamp section; and a 5V4 rectifier. Series one also had beefy transformers
and ran very hot at the plates—around 475
volts. Other similarities to the Pro included
three knobs (not including the power knob)—
Instrument Volume, Microphone Volume, and
Tone—two inputs each for instrument and
microphone, and a 15" Jensen P15N Concert
Series speaker. The amp was cathode bias
and used a paraphase inverter. Like the Pro,
the GA- 70 had sufficient power and volume
to play in a band setting. It had clear highs,
tight lows, and a tendency to break up early.
Cessation of Imitation
The 1957–58 version of the GA- 70 was a
totally different animal—and it was possibly
the best, most influential (albeit indirectly) amp
Gibson ever made. Its name was changed to
the “Country Western,” and the new GA- 70
looked almost the same as the first series,
despite the fact that it had a completely
redesigned circuit. It used two slightly more
robust 5881 power tubes and a cathode phase
inverter, and they gave it more headroom and
a wider dynamic range than the ’ 56 version.
The addition of a power choke helped keep
the current stable and also contributed to the
increased headroom. The new GA- 70 also had
a five-knob control layout with a tone stack of
Bass, Treble, and Fidelity controls along with
the two Volume controls. Significantly, this
tone stack was copied almost exactly by Vox
for the classic AC30 design—right down to
a “mistake” in the fidelity control. For some
reason, on the GA- 70 the treble wipers were
wired 180 degrees in reverse, with the result
being less treble as you turned the control
clockwise. Making the best of this anomaly,
Vox would come to call this a “Cut” control.
The 1958 Gibson catalog described the work
of the tone circuit as follows:
A separate control has been provided for
control of the bass or low frequencies and
for the treble or high frequencies. The use
of these two controls allows the player to
obtain the maximum combinations from
a beautiful clear treble to a deep reso-
nant bass. Setting the “BASS” control at
maximum and the “TREBLE” at minimum,
produces the deepest, fullest bass tone.
Setting the “TREBLE” control at maximum
and the “BASS” at minimum produces a
chime-like tone rich in higher harmonics
and will enable the artist to pick harmonics
with greater ease. When both “BASS” and
“TREBLE” controls are set at minimum the
middle register predominates.
