http://www.ebay.com/itm/270944842040Factory and date codes as follows:
#1: <Right-angled triangle> 6E3 - produced in Heerlen, Holland, 3rd week of May, likely 1966.
#2: <Right-angled triangle> 6G1 - produced in Heerlen, Holland, 1st week of July, likely 1966.
Great for ZBOX.