Dating a JCM 900 1960A
Sadly, Jim Marshall, the Guv'nor, passed away on april 5th Tube humbly salutes the Father of Loud. Jim Marshall started building amps in He did this together with technical friend Ken Bran. Their first amps were very heavily "inspired" marsuall the Fender Tweed 4x10" Bassman. Little did they know then that they were at the threshold of a rock 'n roll revolution Although this division is not entirely accurate, it does give a good impression of the different era's.
The first decade in the history of Marshall is regarded by some as the "Golden Years". Dating websites for over 50 uk the following overview, I try to place the amps in some kind of chronological ordering. Keep in mind that allthough I try to be complete, this is obviously not a complete list, though I datinv it will be some day The very first prototype Marshall jjcm were built in in Jim's kitchen. In these early years the amps, their features and especially the cosmetics varied a lot.
This was the very first Marshall amp. It was built from up to msrshall It didn't actually have a model number at first, but datihg it was called dating marshall jcm 900 JTM The circuit was a Fender Tweed Bassman circuit 5F6-A clone. It is said that the first prototype and early production amps were fitted with two beam power tetrodes, three ECC83's and a GZ34 rectifier tube, but soon KT66 tubes were used instead of the 's.
These amps had 2 channels with each a volume control and two inputs making a total of four inputs. There was also a power switch and a standby switch with a power indicator. Daating first JTM45 amps had no model number printed on them. Later probably in aluminium panels xating used having JTM 45 and MK II printed on them implying the first serie of amps were the MK I's. Bassman Tweed 5F6-A Amp schematic Fender.
These first speaker cabinets didn't have a model number at first. In these cabinets were given the model number They were marehall front cabinets and were fitted with four 12" Celestion G speakers, instead of the four 10" Jensen speakers in an open cabinet like Fender did. These 12" Dating marshall jcm 900 speakers were essentially the same speaker as the Celestion VOX Blue speakers. Late or early the ceramic speakers were replacing the alnico's.
This amp used the bass tremolo chassis in a 2x12" combo cabinet. This was the amp Eric Clapton used dating marshall jcm 900 the dating marshall jcm 900 John Mayall's Bluesbreakers "Beano" album early in Very few of the 2x12" horizontal extension cabinets were built and dating marshall jcm 900 cabinets daring very rare. The speakers were two Celestion G speakers. These G speakers were 'M' magnet speakers with an H cone. These are not the small magnet Gs, but are actually 25W Greenbacks with a different cone, sounding different than a typical 25W Greenback from a 's 4x12 cab.
This amp was in production from to It had 4 channels and 8 inputs. These PA amps had JTM 45 and MK III printed on the front panels. It had 2 channels and 4 inputs. It was the PA version of the It was the Bass version of the The original JTM45 was renamed to this model The tremolo was optional. Photograph of a JTM45 from It datimg the Organ marshal, of the See the Plexi Palace JTM45 page for some great JTM45 pictures.
In Marshall switched to EL34 tubes. To reflect this the JTM45 panels were changed to JTM50 panels. The GZ34 rectifiers were phased during dsting time, allthough there are even JMP 50 models with GZ34 rectifiers. In the first half of the JTM panels were dropped all together and the JMP panels were introduced. So the JTM50 amps dating marshall jcm 900 in production for dating marshall jcm 900 than a year from to By the cabinets were rated as having a maximum power handling of 75 watts.
This increased power handling was probably due to the four Celestion ceramic speakers fitted in these cabinets. These were probably G Greenbacks. In the first prototype and production W amps model were constructed using two 50W output transformers. Shortly later W output transformers were used. The first W Lead and Marshxll models used left over JTM45 panels until some time in but the W PA models did use JTM panels, as these amps sported 8 dating marshall jcm 900 instead of 4, requiring different panels anyway.
The early incarnations of the JTM's varied in design. The JTM's were the first amps to use solid state rectifiers. A tube rectifier was just too much hassle and too expensive. Schematically, all the JTM's are all very similar. The PA version had 4 channels and 8 inputs instead of the marhall 4 inputs and 2 channels. The Tremolo version was an idea narshall Pete Townsend but it wasn't very popular and not many were produced.
This amp had 4 channels and 8 inputs. The front panels were marked with MkV and JTM A lot dating marshall jcm 900 all? Photograph of a Super PA probably from This cabinet was introduced in late It was the first W cabinet being fitted with four Celestion G12M25 speakers. In the top left corner of the cabinet a 'W' logo could be seen.
This amp had 2 channels and 4 inputs. It was the Bass version marshalk T or the Tremolo version of the In Marshall introduced the Marshall jjcm. These amps only had 3 knobs: Treble, Bass and Volume. This early Marshall was also marsyall as "the Pig". In the course of the Low-High tone control circuitry was changed to a Low-Mid-High tone control and these amps were now called the Marshall Majors.
Using four KT88 power tubes, these amps were very powerfull, very loud and very expensive. They were in production up to An ECC82 was used as the driver tube for the four KT88's. Photograph of a rare Marshall head mardhall. The PA Columns were designed to be used in pairs with the Major PA amp. Photograph of a red Marshall PA head thanx to Jesse Petas.
See jck Marshall Arts Major page for more information on these Marshall Majors. In Marshall introduced the 18W "practice" combo amps. Although they were not very datihg, they certainly could "rock".