This tube features a ‘primer’ pin that us used to ensure there are always ions in the gas, thus ensuring that the tube will illuminate instantly when it is dark.
Philips, marked all of their tubes with identifying codes, so it is possible to figure out where and when this tube was made. The format of the markings on this tube is:
- TTT is the type code (MFL in this case)
- C is an internal batch code (3TT in this case)
- F is the factory code (the triangle means Philips, Heerlen).
- Y is 4, which could mean 1974 or 1964
- M is B which means February
This site does a good job of explaining the codes.
Interestingly you can see that the red coating and the above type/batch/manufacturing codes were applied after a previous set of codes was applied. In fact the previous type code is MBT (M8T?), which is the type code for the un-coated version of this tube – the ZM1000. Perhaps the ZM1000R was a special order for RTC? The previous date code is November of 1973/1963. So this tube sat around for about 3 months before being converted to a ZM1000R.