[time-nuts] Boatanchor docs: HP AC-4 counter module manual

David Forbes dforbes at dakotacom.net
Sat Jan 31 23:00:27 EST 2009

O Nuts of Time,

I was recently asked to make a big PDF file of the HP AC-4 counter 
modules manual that I have had on my website for a few years as a 
series of jpeg files. So I did...


These modules are used in the ancient HP 521 to 524 series of 
counters. Each module handles one digit. They have four vacuum tubes 
and either a nixie tube or ten neons in a thermometer arrangement.

I have a 521C and a 522B counter on hand but they are a bit too slow 
to handle the 10 MHz of modern times, having a maximum counting 
frequency of 200 kilocycles per second.


--David Forbes, Tucson, AZ

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