Hewlett Packard AC-4 Series Decade Counters
A bunch of stuff on the HP AC-4 series decade counters. These are tube based, 5963 or 12AU7, decade counters that were used in frequency and other counter units. They were introduced in the 1950's and used in the HP 521A and 524 counters, among others. They were several different versions from the AC-4A to AC-4L. The maximum count rate varied from 120KHZ to 1.2MHZ depending on the unit. They had 10 neon bulbs on the front in a column numbered 0 to 9 and some units used nixie tubes for the display.
I am the proud owner of five AC-4G modules that I got from E-Bay. They look like they are unused. They don't have that used tube equipment smell, if you know what I mean and all of the tubes and components look new. I am going to build them into a hare-brained idea that I have will post the results here sometime in the future.
