[time-nuts] Restoring GR 1120-AB Frequency Standard

phil fortime at bellsouth.net
Fri Aug 22 23:15:22 EDT 2008

----- Original Message ----- 
From: "Magnus Danielson" <magnus at rubidium.dyndns.org>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Friday, August 22, 2008 5:25 PM
Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard

> phil wrote:
>> Gentlemen,
>> Original poster is trying to "RESTORE" this entire old General Radio
>> Standard ( a rack of equipment) to it's "original" glory.
>> He simply needs a part, a unique thermoswitch or a way to fix it, not
>> retrofit an atomic engine! This is a museum class instrument, 100kc.
>> May I suggest start a new thread on the better/best merits/design of
>> temperature control.
>> Makes it rather difficult to follow a thread as the subject has changed.
> My proposal to use capacitive sensing rather than conductive sensing
> would handle the electrode oxide issue. It is meant as a means to go
> around the sensing issue with parts at hand and only some new electronic
> design of very simple form, not the means to supercalibrate something.
> I guess this only shows that time-nuts are time-nuts...
> Cheers,
> Magnus

Perhaps this will help understand why I made that comment.

That old "primary" standard was quite a contraption. This things heyday was 
in the order of 1950's and used up into the 60's and some models into early 
70's. Of course it was all tube equipment.

My unit model was possibly a 620, it predated what Russ has (1100) but was 
quite similar in design. Russ's unit has all the multivibrators in one 
housing where mine was each separate. I think his is a 100kc oscillator and 
mine was 50kc.

As I remember the one I had was in two 7-foot racks, a standard side and 
frequency measuring side. My oscillator was 50KC though about 300 dollars in 
the mid 6o's would have bought a 100kc quartz bar to upgrade it

The unit had each module or circuit in a separate 19" rack space all 
averaging 8 inch high The main components, a power supply, oscillator (about 
20 plus rack inches high by itself), separate multivibrators of 100kc, 10kc, 
1kc, and 100 cycles. Yes they were called multivibrators though all tube. It 
also had a syncronometer at the top of the rack, better known as a clock. 
Apparently the crystal was rich in harmonics and they made use of it in this 
assembly. That clock ran off of the 1 kc output.

The heart of the oscillator, main part of this contraption used a quartz bar 
about 3/8 of an inch square and about 2 inches long suspended on 4 springs. 
If I recall it was a single oven but it's specs called for about .01-degree 

I don't remember all the fine details, but it had many other components (all 
seperate rack units), a separate 5kc interpolation oscillator, amplifier, 
and even an 8-inch speaker to zero beat the standard to another unit, 
talking about phase lock!

So as you can see, these vintage units only use/value is that of an antique 
or conversation piece. A 10811 would blow it away performance wise.

Now with an understanding of that old antique, that discussion was like 
putting an electronic ignition in place of the old Ford Model T spark coil. 
You could, but .. You just search for the part.

So it's not a "time-nut" issue as such other than appreciating the history 
or the evolution of time. I can see from the varied posts this is one heck 
of a super talented group. I guess we all get involved in something 
interesting and easily get carried away, as in the discussion. Granted you 
can do a given task many ways, and bantering ideas around is how things are 
born and perfected. Only problem is, it doesn't locate an "original" antique 
part, what he stated he wanted!

That old GR stuff does occasionally show up, most free to haul off it's so 
massive. A bunch of the old vintage GR standard parts was listed as a lot on 
ebay some months ago.

Someone asked what happened to my old GR stuff. I disposed of over 100 tons 
of old electronics that had accumulated including this old GR stuff.  One of 
my sidelines was the used equipment business and the sales of tube stuff 
died. I had some 15,000 feet of "junk" as I call all this stuff.

By the way, according to Bruce, that design of the old "thermoswitch" 
achieved resolutions as fine as .001 degrees.

It would be hard to build any electronic sensor of any design that is that 
reliable and repeatable (.001 degree) with a "one-time" factory calibration 
good for a life exceeding 50 years without using a similar sensor design. 
The unit in question with the electrode in mercury design lasted about 50 
years before showing it's age and misbehaving.


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