Vox Amp Serial Number Dating
Probably a better 'Vox' than the 70's models anyway. I don't have a ton of experience with 'em, but the Korg reissues (like yours) are well regarded.
Dating AC50s. Serial numbers, unfortunately, are not a wholly reliable means of dating early AC50s, that is to say, amps made from December 1963 to mid 1965. In large part, this is a result of production practice. 
Triumph Electronics, based in Purley in South London, made the chassis.
The early JMI Vox from pre 1968 are the true classics, 70's & 80's have their ups & downs (but aren't considered great); 90's and early 00's are good reissues; current Chinese-made reissues have their fans and can sound great. But have the stigma. Play and enjoy, don't worry about it much, and you'll be able to sell at a good price when you're ready.
Dating AC50s Serial numbers, unfortunately, are not a wholly reliable means of dating early AC50s, that is to say, amps made from December 1963 to mid 1965. In large part, this is a result of production practice., based in Purley in South London, made the chassis. These were then taken by road to Dartford, where back panels (with serial number plates) and boxes were supplied. In the process of loading, unloading and storing, any order that might have existed in the Triumph workshop was lost. There may be 'patterns' here and there, but nothing that one can rely on. An early Triumph chassis (serial no. Control panels were sent by JMI to Purley for final assembly.
The chassis, as mentioned, were then taken to Dartford, where the back panels were attached (the connectors soldered to the terminals in the amp), and the chassis screwed into the boxes that had been assigned. All is not lost however. One can often get a good general sense of date from the type of box, whether or not the amp has a valve rectifier, and last but not least, from the two-letter date codes on the potentiometers. Serial number 1727. Some of the pots are replacements, but the one indicated is original and bears the code 'GL'. 'L' = 1964, and 'G' = July. The first letter is the month: 'A' = January, and so on.
Dating Vox Amps
The second letter is the year: 'K' = 1963, 'L' = 1964, 'M' = 1965. Potentiometers were naturally bought in batches, each batch lasting several months. But one nonetheless has a good terminus post quem ('date after which'). The same is true for the blue Hunts capacitors used by Triumph from 1964 - 1965. For the date code system employed on these,.
By early to mid 1965, Burndept Electronics, which shared a building with Vox off West Street in Erith,Kent, took over the bulk of production, and serial numbers consequently become more reliable as a means of dating - Burndept was a much more orderly place than Triumph. It should be said, however, that the Burndept chassis numbers stamped on the aluminium upright underneath the input jacks do not run in sequence with the serial numbers. Early solid state rectified AC50 - only two main valves. There is no serial number plate on this amp, but the potentiometers are dated January 1965. Solid state rectification - the AC50 mark 3 with brimistor The brimistor - a type of temperature dependent resistor designed to delay in-rush current and voltage - was marked as addition on schematic OS/072 (14th October 1965), and first appears in amps around serial no. AC50 number 4133 has a brimistor, but no.
Vox Amp Serial Number Lookup
4282 does not. The transition took a little while.