These amps run at much lower voltages than the later KT66 amps, producing less power while being easier on the tubes.
The model numbers can be somewhat confusing because model numbers such as 1987 or 1959 can be mistakenly interpreted as the production year of the amplifier.The JTM 45 was first built in 1962, handmade in an all-aluminum chassis, by Ken Bran and Dudley Craven.Because of its power, Marshall decided early on to build it as a head, with a separate 4×12" cabinet with Celestion speakers.Sadly, Jim Marshall, the Guv'nor, passed away on april 5th 2012. These amps were built as heads (or tops) separated from the speaker cabinets. These amps were introduced in april 1981, around the same time as the JCM800 series. These amps were more or less a copy of the Fender 1959 Tweed Bassman. This was the combo version of the 2098 Master Lead head. The 2000 Lead and 2001 Bass heads are probably the loudest and most powerfull Marshall tube amps ever built.