These are codes often seen stamped on components found in US made vintage tube equipment.
This list is circa 1955, and some codes have been reassigned or added since that time.
The first string of numbers is usually the part number, or sometimes the pot value.
Finally, a word of caution: This method applies only to American made pots and not all potentiometer manufacturers subscribed to the EIA source code date.
Here is a brief listing of the manufacturers Source Code numbers: 34 – Cornell-Dubilier Electronics (made capacitors used on early Fender Guitars and are the ones that were paper and wax coated.
They now make polyester film capacitors) 106 – Allen-Bradley Corp.
In the chart below you will see the letters that coincide with the year and month of the amps manufacture.
The first letter is the year and the second letter is the month. If the tube chart is not in the amp or has been torn or damaged and you cannot read the ink stamped letters you can date the amp by the codes on the potentiometers.