Re: ENIAC Tubes (Valves). While I think there were a goodly number of 6SN7s used in the machine, the miniature devices you cite [12A -X7 -U7 -AT7] were still finding their way out of WWII secrecy into the mainstream market. As far as I cans research, none were used in the machine, which was *designed* in the early 40s, and of course built from those designs over the space of about two or three years. I no longer have access to my library on the subject, or I would be a little less vague. FWIW, the ENIAC rack in the Computer Musem at Moffet is populated mainly with 6SK7s, a metal-bodied pentode with a grid cap. I don't remember at this remove of time what the function of that particular rack was in the overall computer. I took several shots of it, and also shamelessly and wantonly ingnored the stern and forboding "Do Not Touch" sign, reached over and clicked one of it's multi-position selector switches. Yes, I did. "What're ya in for, buddy?" "Clicked a switch on the ENIAC. And you...?" "Tore th' tag offen my new mattress." "Yeah. Tough break. Well, see yas in the Exercise Yard..." Cheerz John