Hi Tim,
We missed you at the 4th annual light bulb shindig this year. Maybe next year? I have a comparable instrument with the contact button built into the side of the volt meter. It is marked "Talmont, New York". It also has what appears to be porcelain or plaster in the male end of the socket. I know this isn't much help but it's the best I can do. Good luck with your research and if you find out more info, please post it. Thanks, Tim