Keep in mind that no reliable serial number information exists for pre-1969 Marshall amps, so if your amp doesn't have a number matching one of the formats below, it is likely pre-1969 and identifiable by features rather than serial number.
Click on the links here to jump directly to the serial number style that matches your instrument: The earliest Marshall amp models did not have model codes or any official serialization, though some models had a simple sequential four-digit numbering system inside the back panel.
These numbers supposedly started with 1001 and progressed from there, starting with 2001 at the beginning of 1964.
Often these specimens produced between October 1962 and December 1964 had an offset chassis.
Production has continued there uninterrupted through today, though some lower-priced models are now made in China, India or Korea, depending on the series.
JTM-45 Models: 1962 - 1966 Bluesbreaker Combos: 1964 - 1972 Four-Digit Models (no series): 1965 - 1981 JCM 600 Series: 1997 - 1999 JCM 800 Series: 1981 - 1991 JCM 900 Series: 1990 - 19 Series: 1998 - 2008 Silver Jubilee Series: 1987 - 1989 30th Anniversary Series: 1992 - 1999 JTM Series: 1995 - 1998 35th Anniversary Series: 1997 only Solid State 5000 Series: 1984 - 1991 Valvestate Series: 1991 - 2000 AVT Series: 2000 - 2007 Mode Four Series: 2003 - 2008 MB Series: 2006 - 2012 Hand-Wired Reissue Series: 2004 - present JVM Series: 2007 - present Vintage Modern Series: 2007 - present Haze Series: 2009 - present MA Series: 2009 - present MG Series: 1999 - present JDM:1 Series: 2010 - present Some amps won't fit into these series (like the recent Class 5 Combo or various signature and limited edition models), so using the serial number will be your best bet to hone in on a specific date of manufacture.
*) AC/DC version was available, sometimes known as EH-110. **) AC/DC version was available, sometimes known as EH-160 (one sample can be found in Aspen Pittman's book, 3-6C5, 4-26B6, 4-25Z5). ***) AC/DC version, known as EH-195 was also available GA-77 Vanguard: 12AY7, 12AX7, 12AU7, 2-6L6, 5V4 GA-70: 12AX7, 12AY7, 12AU7, 2-6L6, 5V4 GA-55: 2-12AY7, 6SC7, 2-6L6, 5V4 GA-45 Maestro: 2-5879, 6SQ7, 12AX7, 2-6V6, 5Y3 (essentially a GA-40 with bass & treble tone controls and different speaker configuration)GA-40 Les Paul: 2-5879, 12AX7, 6SQ7, 2-6V6, 5Y3 GA-30 Invader: 2-12AX7, 12AU7, 2-6V6, 5Y3 GA-20: 4-12AX7, 2-6V6, 5Y3 (correspond to Epiphone EA-25 Century) GA-20T: 5879, 12AY7, 12AX7, 6SQ7, 2-6V6, 5Y3 (correspond to Epiphone EA-25T Century) GA-15: 12AX7, 6SL7, 2-6V6, 5Y3GA-9: 6SJ7, 2-6V6, 5Y3 GA-8 Gibsonette: 12AX7, 2-6V6, 5Y3 GA-8T Gibsonette/Discoverer: 12AX7, 2-6BM8, 5Y3 GA-6: 12AY7, 6SL7, 2-6V6, 5Y3 GA-6 Lancer: 2-12AX7, 2-6V6, 5Y3 (identical to GA-14 Titan except for 12" speaker) GA-5 Skylark: 12AX7, 6V6, 5Y3GA-400 Super-400: 3-12AX7, 12AY7, 2-6BJ8, 2-6SK7, 6V6, 2-6550, GZ34 GA-200 Rhythm King: 2-12AX7, 12AY7, 2-6BJ8, 2-6SK7, 6V6, 2-6550, GZ34 GA-46T: 3-12AX7, 2-5879, 6SN7, 6V6, 2-6550, 5AR4 GA-85: 2-12AX7, 2-5881, 5V6, 5V4GA-100 Bass: 6EU7, 2-6BD6, 2-6FM8, 2-6L6, GZ34, 0A2 (correspond to Epiphone EA-70 Bass-Amp) GA-86 Ensemble: 2-12AX7, 2-5881, 6V6, GZ34 GA-80 Vari-Tone: 2-12AX7, 2-5879, 2-6L6, GZ34 GA-16T Viscount: 2-12AX7, 2-6V6, 5Y3 GA-14 Titan: 2-12AX7, 2-6V6, 5Y3 (identical to GA-6 Lancer except for 10" speaker, and Epiphone EA-30 Triumph)GA-83S Stereo-Vib: 4-12AX7, 12AU7, 3-6CG7, 4-6BQ5, GZ34 GA-88S Stereo-Twin: 3-12AX7, 4-6BQ5, GZ34 GA-87 Maestro Stereo: 3-12AX7, 4-6BQ5, GZ34 GA-78 & 79: 4-6EU7, 4-6BQ6 GA-79RVT Multi-Purpose: 3-6EU7, 7199, 12AU7, 4-6BQ5 GA-78RV Maestro 30: 3-6EU7, 7199, 12AU7, 4-6BQ5GA-1RT: 12AX7, 6BM8, 5Y3 GA-1RVT: 6EU7, 7199, 6BM8, 5Y3 (Aka Maestro M-1RVT) GA-2RT: 4-6EU7, 12AU7, 2-6V6, 5Y3 GA-77RV Vanguard: 3-6EU7, 1-12AU7, 2-6L6GC, 1-GZ34 (5AR4) GA-30RV Invader: 3-6EU7, 12AU7A, 2-6V6, 5Y3 GA-15RV: 3-6EU7, 12AU7, 2-6V6, 5Y3 GA-19RVT: 3-6EU7, 7199, 2-6V6, 5Y3GA-40T Les Paul: 3-6EU7, 12AU7, 2-7591, 5AR4 GA-60 Hercules: 2-6EU7, 2-7591, 5AR4 (correspond to Epiphone EA-65 Rivoli) GA-18T Explorer: 2-6EU7, 2-6BQ5, 6CA4 GA-8 Discoverer: 6EU7, 6C4, 2-6BQ5, 6CA4 (correspond to Epiphone EA-35 Devon) GA-8T Discoverer: 2-6EU7, 2-6BQ5, 6CA4 (correspond to Epiphone EA-35T Devon) GA-5 Skylark: 6EU7, 6C4, 2-6AQ5, 6X4 (correspond to Epiphone EA-50 Pacemaker) GA-5T Skylark: 2-6EU7, 2-6AQ5, 6X4 (correspond to Epiphone EA-50T Pacemaker) Courtesy of Allan Fredrickson.