My father had to make tubes for a lab course as an EE student at Cornell in the early 50s. I have some of them and the lab report. They ranged from simple diodes up to 6K6GT pentode. Rob Flory robandpj at earthlink.net www.home.earthlink.net/~navyradio WWII Navy Radio www.home.earthlink.net/~robandpj Les Flory Television and Electronics