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

wa3frp at aol.com wa3frp at aol.com
Sat Aug 23 23:21:58 EDT 2008

Max is correct.

The GR 1120-AB contains the following units in a standard relay rack:

The GR Standard Frequency Oscillator 1113-A with an output frequency of 
5 MHz. This unit is settable to 1 x10 -10 with an output of 1 V RMS.

Located in the relay rack above the Standard Frequency Oscillator is 
the GR Frequency Divider 1114-A (all discrete transistor) with inputs 
of 5 MHz, 1 MHz and 100 MHz and outputs of 1 MHz (Sine), 100 kHz (Sine 
+ Square), 10kHz (Sine + Square), 1 kHz (Sine) with two output jacks 
and 100 Hz (Sine) with two output jacks. There were plug-in options 
that provided additional outputs of 400 Hz and 60 Hz output but 
unfortunately I don't have either option installed.

Installed in the relay rack above the Frequency Divider is the GR 
Syncronometer Time Comparitor 1103-B. The GR 1103-B uses a 1 kHz motor 
and 24 hour clock to display the integral of the number of cycles 
executed by the standard frequency oscillator as a standard time 
interval. The GR 1103-B contains a set of dry contacts that open one 
each second for 0.05 seconds. In the mid-1960s, this time standard was 
compared to a standard time radio station, such as WWV, using the GR 
1103-B. While this a beautiful piece of mechanical gear, a HP 117A is 
much easier to use.

The bottom of the relay rack includes the Battery Storage drawer, the 
GR 1268-A Automatic Battery Charging Unit and the GR 1116-B Emergency 
Power Supply. These three pieces of equipment are capable of 
maintaining power to the rack for four hours in the case of commercial 
power failure.

This particular GR 1120-AB, rack number 195, was donated by General 
Radio to the Moore School of Electrical Engineering - University of 
Pennsylvania in 1965. The equipment was assigned to the School's Valley 
Forge Research Center in the late 1960s and remained there serving as 
the time standard for a number of research projects. By the late 1970s, 
the GR 1120-AB was stored in an unheated area at Valley Forge and was 
unused. I was granted approval to remove the Standard after approaching 
the administration at Penn. Otherwise, it would probably be in a 
landfill today.

My work to completely electrically and mechanically restore this 
Standard started in May 2004. Once the inner oven thermoswitch is 
replaced and tested, the Standard will be completely operational. 
Probably one of the few remaining GR 1120-AB racks in the world.

-----Original Message-----
From: Max Robinson <max at maxsmusicplace.com>
To: Discussion of precise time and frequency measurement 
<time-nuts at febo.com>
Sent: Sat, 23 Aug 2008 1:19 am
Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard

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 
of were discrete transistor construction. Seems to me the clock used a 
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.


Max. K 4 O D S.

Email: max at maxsmusicplace.com

Transistor site http://www.funwithtransistors.net
Vacuum tube site: http://www.funwithtubes.net
Music site: http://www.maxsmusicplace.com

To subscribe to the fun with tubes group send an email to,
funwithtubes-subscribe at yahoogroups.com

----- 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, 
>>> 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 
>> 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 
>> design of very simple form, not the means to supercalibrate 
>> 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 
> 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 
> and
> mine was 50kc.
> As I remember the one I had was in two 7-foot racks, a standard side 
> frequency measuring side. My oscillator was 50KC though about 300 
> 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 
> It
> also had a syncronometer at the top of the rack, better known as a 
> Apparently the crystal was rich in harmonics and they made use of it 
> this
> assembly. That clock ran off of the 1 kc output.
> The heart of the oscillator, main part of this contraption used a 
> 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 
> (all
> seperate rack units), a separate 5kc interpolation oscillator, 
> 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 
> 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 
> or the evolution of time. I can see from the varied posts this is one 
> 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 
> 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 
> 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. 
> of
> my sidelines was the used equipment business and the sales of tube 
> 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 
> reliable and repeatable (.001 degree) with a "one-time" factory
> calibration
> good for a life exceeding 50 years without using a similar sensor 
> The unit in question with the electrode in mercury design lasted 
about 50
> years before showing it's age and misbehaving.
> Phil
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to 
and follow the instructions there.

More information about the time-nuts mailing list