[time-nuts] 60Hz power line derived timebases

Magnus Danielson magnus at rubidium.dyndns.org
Sun Dec 13 12:56:08 UTC 2009


Geoff Blake wrote:
> I don't know about 60Hz timebases for older UNIX systems, but I do
> remember low end frequency counters being offered with mains derived
> timebases - I remember them as a catalog item, I never saw one!
> 
> I think they were offered by Systron Donner and this was probably back in
> the '60's. They even did a 50Hz option - it must have been a real
> time-nuts guessing-stick!

HP did the same thing, and I have one of those. The HP could be trimmed 
to 50 Hz, 60 Hz or 100 Hz as the phantastron divider would generate 10 
Hz for the 0,1 s gate time. Considering that this is a 5 digit counter 
(ehm.. actually there is no digits but columns of 0 to 9 bulbs) it may 
work well enought for most applications. For highend users there is a 
high-stability crystal option, which is a 100 kc crystal oscillator 
divided down by a set of 3 phantastrons to 100 c and then replaces the 
mains feed. My counter has the crystal option. :)

As for the original question, I beleive that DEC have provided mains 
feed already from the PDP-1. I seem to recall it. For UNIX the PDP-7 and 
PDP-11 is the relevant early machines. But getting the 50/60 Hz does not 
get you local or GMT time (which was relevant then) so you still had to 
set it from armwatch or use a modem service.

Cheers,
Magnus



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