"The Best Amplifier Since the JTM 45; The 1969 50-Watt"

1969 Marshall JMP-50 Plexi (Model 1987 Lead & Bass)

An all original, 1969 50 watt Marshall JMP-50 Plexi Head (Model 1987 Lead & Bass). This amplifier has just been fully serviced by Doug Anderson (Tone Zone, Altadena, CA) and is in perfect working order. The amplifier has  been converted to USA 115 voltage.
Dimensions:
Width: 25 3/4 inches
Height: 9 1/2 inches (including rubber feet)
Depth: 8 1/4 inches
Weight: 33 lbs.
Specifications:
Tubes: Preamp - 1 x ECC83 & 2 x AX7; Output - 2 x EL34;
Output transformer: "784-139"
Power transformer: "1202-118"
Inputs: Four
Controls: On/Off switch; Standby switch; Indicator Light; Presence; Bass; Middle; Treble; Volume I; Volume II.
Cabinet covering: Black Levant Vinyl

Most versions of these amplifiers were sold as head cabinet, with a smaller quantity configured as combos. The most famous combo was the JTM 45 Tremolo 2x12 played by Eric Clapton when he was with John Mayall's Blues Breaker's; which is why the JTM 45 is known as the "Blues Breaker". During this period, the JTM 45 and JTM 50 were offered with or without tremolo, in both head and combo versions.
 
"By early 1966, the "JTM 45" description was supplemented, typically for PA amplifiers, by the "JTM 50", and at about the same time the cream back panels were replaced by a Plexiglass version to match the front. The reason for the apparent upgrade from 45 to 50 watts was most likely due to marketing considerations -- after all, "50" sounded better than "45" -- but the component improvements that had occurred since 1962, such as the type of resistors used and the transformer specifications, must also have played a part. By 1966 the JTM 45 and 50 had seen dramatic cosmetic changes and developed an appearance that was to be Marshall's house style for the next few decades. The sound had been honed to meet the demands of the new generation of rock guitarists, and Marshall were well set to take full advantage of the unparalleled musical changes that were about to sweep the world during the "swinging sixties"… As the years passed by, Marshall were making small but continual changes and refinements to their amplifiers, and by 1968-69 they had built what was in my view the best amplifier since the JTM 45; the 1969 50-watt. Every one of these that I have owned has had the capacity to provide a sparkling clean sound, through JTM 45-like crunch, to a distortion that's just on the sane side of heavy metal; and it's all available at the twist of the volume knob. Great stuff!" (Michael Doyle. The History of Marshall, pp. 20 & 28).