Gibson amplifiers have become known amongst guitarists for their warm, consistent sound and reliability. While you may be willing to pay a high price for a vintage Gibson amp, you should always verify the date of the amp to avoid being ripped off. By verifying the date of manufacture of the Gibson amp you want to buy, you will be able to breath easy that you are getting an authentic amp for the right price.
Locate the speaker which can be found in the back of the amp.
Find the source code stamp, which is a series of six or seven numbers, that will be stamped on the speaker. The stamp can be found on any part of the speaker, but it will be readily visible no matter the location.
Write out the source code and divide it into three sections. The first three numbers represent the company that made the speaker, the fourth (and fifth if there are seven numbers) represent the year the part was made, and the last two numbers represent the week that the part was made during that year.
Make note that a source code beginning with 220 was made by Jenson, 328 by Utah, 285 Rola, 137 CTS and 134 by Centralab. Amps with Utah speakers are usually dated to 1945 and earlier, and Rola speakers from the late 1940ss and early 1950s. Jenson speakers are from the 1950s, and CTS and Centralab speakers were used from the 1960s onward. This is good to know if you have a six number source code as the year number can then be lined up with the right decade to properly identify the year the amp was made.
Contact the Gibson company if the source code cannot be found, or has been rubbed off, and read them the serial number found on the back of the body of the amp. While the serial numbers were randomly assigned and do not immediately tell you the age of the amp, Gibson has a large database of serial numbers that than can search to find out which year and week that your amp was made.
Always verify the serial number of a vintage Gibson amp with the company before purchasing the amp. It is always good to verify the age that the serial number suggests with what the speaker source code suggests to ensure you are paying for the amp you think you are getting.