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ELECTRIC SS AMPS: THIRD SERIES PIGGYBACK MODELS (1969-1971)

In 1969, Ampeg introduced their third series of solid-state amps, and they also went away from the Portaflex design to a more traditional piggyback design with separate heads and cabinets (because of this, amps in this section are evaluated with separate head and cabinet prices because they are often sold in the vintage market without one another). The third series featured a mixture of carryover models from 1968 (BT-15, BT-140, ST-22, ST-25, and ST-42) as well as new models (BT-25, BT-25L, SBT, and SST). Ampeg also introduced their "70s" cosmetics with black covering, a blue/silver grille, and large Ampeg logo with shield. Most amps in this series weren't produced very long and only lasted through the late 1960s or early 1970s.

Models (9)

BT-15 SECOND VERSION

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- 85W, 1-15 in. speaker, multi-purpose combo/piggyback Portaflex design, solid-state chassis, two channels, front chrome control panel, four inputs (two per channel), six knobs (Ch. 1: v, t, b, Ch. 2: v, t, b), ultra hi switches for each channel, polarity switch, power switch, external speaker jack, external amp/line out jack, black covering, blue/gray grille cloth, 21 in. wide, 24 in. tall (closed), 14 in. deep, 70 lbs., four-wheel dolly included, mfg. 1968-69.
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BT-25

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- 120W, 2-15 in. CTS speakers in a column style cabinet, piggyback-style bass amp with separate head and cabinet, solid-state chassis, two channels, front silver control panel, four inputs (two per channel), six knobs (Ch. 1: v, t, b, Ch. 2: v, t, b), hi and lo switches for each channel, polarity switch, power switch, black covering, blue/gray grille, mfg. 1969-1971.
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BT-25L

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- similar to the BT-25, except has 2-15 in. Altec Lansing speakers, mfg. 1969-1970.
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BT-140 SECOND VERSION

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- 100W, 2-15 in. JBL D-140F speakers in a column style cabinet, piggyback-style bass amp with separate head and cabinet, solid-state chassis, two channels, front top silver control panel, four inputs (two per channel), six knobs (Ch. 1: v, t, b, Ch. 2: v, t, b), hi and lo switches for each channel, black covering, blue/gray grille, mfg. 1969-1971.
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SBT

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- 120W, 4-15 in. 421A Altec speakers (2-15 in. speakers in each cabinet), bass piggyback with two speaker cabinets, solid-state chassis, two channels, silver front control panel, four inputs (two for each channel), seven knobs (Ch 1: v, t, b, mid-range, Ch. 2: v, t, b), ultra hi and ultra lo switches for each channel, Ch. 1 mid-range freq. select, black covering, blue/gray grille, mfg. 1969-1971.
Ampeg borrowed a design from the Acoustic 360 in the SBT by including only the pre-amp in the head unit and adding a separate power amp to drive each speaker cabinet. The speaker cabinets featured input jacks, a level control, and an on/off switch as well as a four-wheel dolly. Because the head alone is unable to drive a normal speaker cabinet, it is virtually worthless without the cabinets it was sold with originally.
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SST

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- 120W, 4-12 in. 417B Altec speakers (2-12 in. speakers in each cabinet), guitar piggyback with two speaker cabinets, solid-state chassis, two channels, reverb, tremolo, vibrato, silver front control panel, four inputs (two for each channel), 10 knobs (Ch 1: v, t, m, b, vibrato s/vibrato i, tremolo s/tremolo i, Ch. 2: v, t, b, All: echo dimension), switches for Ch. 1: midrange cut, midrange boost, ultra hi switch, midrange freq. selector, three-way ultra lo switch, reverb on/off switches for Ch. 2: reverb on/off control, ultra hi, ultra lo, black covering, blue/gray grille, mfg. 1969-1970.
Ampeg borrowed a design from the Acoustic 360 in the SST by including only the pre-amp in the head unit and adding a separate power amp to drive each speaker cabinet. The speaker cabinets featured input jacks, a level control, and an on/off switch as well as a four-wheel dolly. Because the head alone is unable to drive a normal speaker cabinet, it is virtually worthless without the cabinets it was sold with originally.
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ST-22 GLADIATOR

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- 120W, 2-12 in. Altec Lansing speakers in a column-style cabinet, piggyback configuration, solid-state chassis, two channels, tremolo, vibrato, reverb, front top silver control panel, four inputs (two per channel), nine black and silver knobs (Ch. 1: v, t, b, s, i, r, Ch. 2: v, t, b), polarity switch, power switch, black covering, blue/gray grille, mfg. 1969 only.
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ST-25 OLYMPIAN

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- 120W, 2-15 in. Altec Lansing speakers in a column-style cabinet, piggyback configuration, solid-state chassis, two channels, tremolo, vibrato, reverb, front top silver control panel, four inputs (two per channel), nine black and silver knobs (Ch. 1: v, t, b, s, i, r, Ch. 2: v, t, b), polarity switch, power switch, black covering, blue/gray grille, mfg. 1969-1970.
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ST-42 COLOSSUS

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- 120W, 4-12 in. Altec Lansing speakers, piggyback configuration, solid-state chassis, two channels, tremolo, vibrato, reverb, front top silver control panel, four inputs (two per channel), nine black and silver knobs (Ch. 1: v, t, b, s, i, r, Ch. 2: v, t, b), polarity switch, power switch, black covering, blue/gray grille, mfg. 1969-1970.
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