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

Max Robinson max at maxsmusicplace.com
Sat Aug 23 01:19:39 EDT 2008


There must have been several different versions of this unit.  The 
oscillator I have is 5 MHz.  The frequency dividers in the rack I got it out 
of were discrete transistor construction.  Seems to me the clock used a 25L6 
although I don't remember how they derived the heater voltage.  There was 
also a phase locked frequency multiplier with outputs at 10 MHz, 100 MHz and 
1 GHz.  The frequency divider module had outputs down to 1 PPS.

After typing that I'm not sure the oscillator frequency is right.  Maybe 
it's 1 MHz.  I'm sure it's not 100 kHz.

Regards.

Max.  K 4 O D S.

Email: max at maxsmusicplace.com

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----- Original Message ----- 
From: "phil" <fortime at bellsouth.net>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Friday, August 22, 2008 10:15 PM
Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard


>
> ----- 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
>
>
> 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
> regulation.
>
> 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.
>
> Phil
>
>
>
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