Clockwise from top left, 1947 GA-25, 1950 GA-50, 1951 GA-20, 1959 GA-5T, 1957 GA-6
Clockwise from top left, 1947 GA-25, 1950 GA-50, 1951 GA-20, 1959 GA-5T, 1957 GA-6
Gibson started out making amplifiers for their Electric Hawaiian guitars in the 1930s. Production was suspended during the Second World War, but resumed in about 1946. From the late 1940s to the late 1960s, Gibson made a line of guitar amplifiers that rival the much better known Fender amps in tone and surpass them in quality. Gibson's customers were mostly jazzmen and I'm guessing they were looking for a smooth mellow tone. These Gibson amps are indeed mellow and smooth. With all due respect to the current Gibson advertising, when the old guys go on and on about tone, this is what they're talking about!
The oldest amp in my collection is this 1947/48 GA-25. The GA-25 was apparently only manufactured in 1947, but the EIA code on the speaker identifies it as being manufactured in 1948, so I guess some GA-25s were still being made in early '48. In any event, this is a very rare amplifier. This one really sings. It has two superb Jensen speakers, a P12R and an 8-inch. These permanent magnet-type speakers represented a new direction for Gibson, which had used field-coil speakers up until this model.
The GA-25 uses a single 6SJ7 preamp tube and a pair of 6J5s as phase splitters. The power tubes are a pair of 6V6s. A 5Y3 rectifier tubes completes the set.
Next is another pretty rare amplifier, this 1950 GA-50. This amp has gorgeous tone, very smooth and mellow. When I got it, it had next to no gain. To get any volume at all out of it I had to crank it all the way to 10. I relaced one of the 6SJ7 preamp tubes, and that fixed the problem. Like the GA-25, the 50 has two Jensens, a PM12G and a 8-inch. It's in pretty good shape, except for the handle, which is long since gone, and some damage to the case under the handle area where someone drilled a hole and installed what I assume was meant to be a headphone jack, and another, larger hole with nothing but hole in it.
This particular amp is the regular model (no tremelo), so it has a pair of 6SJ7 preamp tubes and a pair of 6J5 types as phase splitters, like the GA-25. The power tubes, however, are the 6L6 type. The rectifier is a 5Y3. This amp has seven tubes and the GA-50T had one more. Amps were promoted on the number of tubes they contain, with more, presumably, being better. A bit like computer clock frequency today.
This is a 1951 GA-20. The first amp to get this "medallion" look was the BR-6 amp in 1947. This amp is in very good condition except the leather handle is rotted away. The preamp tubes are a pair of 6SJ7 types, one Raytheon and one CBS. The phase splitter is a 6SL7, also a Raytheon. The power tubes are Raytheon 6V6-GTs, and it uses a 5Y3 rectifier. The speaker is the superlative Jensen P12R Alnico 5 PM Concert series. The GA-20 was Gibson's first post-war design to use a top-mounted chassis, with the tubes hanging down. This amp had a bad case of blown filter caps, but a short stay at Torres Engineering fixed that right up.
Here is my 1957 GA-6. 1957 was a very good year and a lot of us '57 models are still going strong! This amp is no exception. It's been through a lot in its 44 years. It has another Jensen P12R Alnico 5 PM Concert Series. It's been reconed at some point, and the amp's electronics have had at least one good rebuild. When I got it it had a nasty hum, which, according to Dan Torres, did not sound like bad filter caps (the bane of old amps everywhere). Dan had this amp for a couple of months and eventually had to devise a whole new way to test speaker-mounted transformers before he figured out it was a bad transformer. Now it's a quiet as, well, it was built to be.
This GA-6 used the more modern 12AX7 preamp tubes instead of the octal types that the older models used. The power tubes are two 6V6 tubes, and the rectifier is a 5Y3. The 6V6s are nice old GE JAN 6V6-GTs.
And lastly, Gibson's answer to the Fender Champ. This is the GA-5T. The "T" denotes tremelo. GA-5s started out as Les Paul Jr amps in the early '50s, but by 1957 were designated GA-5. This one, in blonde tolex and oxblood grille, is from 1959. This is a real nice single-ended class-A amp, with wonderful tone. Occasionally, I put an overdrive pedal in front of it and then it just rocks. Killer sound, sustain for ever. Just way too much fun.
This GA-5T has a Jensen Special Design speaker, a 6SJ7 preamp tube, a 6V6 power tube and yet another 5Y3 rectifier. The tubes in this amp have "Gibson" stencilled on them, leading me to assume that they are the original tubes. This was another amp that I got with a bad filter cap in it. When we opened it up, it was pretty much the first time since it was built that the chassis panel had been removed. Nice new filter cap from Torres Engineering and it was ready to rock.