Not something i have ever noticed i will look for it now

yep as i said they did change the dimples between 1c and 1f. check your lamps for confirmation

please excuse my sense of humour but it has been terrilble

Interesting comparison! No design change was made and the dimples should always be small with pointed tips, and have the appearance of a cat eye when observed from directly end-on. However they tended to grow over time due to gradual wear of the cast iron moulds. After new moulds were installed there would be a sudden decrease in dimple size. This became particularly pronounced for the low watts line not long before closure of Hamilton - they had hoped to continue running up to the end with the same moulds but in the end they became crazy huge, and it was necessary to make a major investment in new tooling for only a short period of production. I seem to recall one of the Hamilton engineers mentioning that new moulds were needed approx every 10 years.

Are the moulds possible to make by CNC from blocks of Iron ? How about the rest of the tooling for the discharge tube ?

when i visited hamilton in 2014, june -the person told me the dimples were changed in the lower wattage lamps to keep the sodium in them for longer? since 2011 all the dimples have been like this in the <55w lamps