GRC movements were available with either 120vac (US mains voltage; often equivalently stated as 117v, 115v, and/or 110v) or 24vac motors. A 24vac system can be installed using class-2 low-voltage wire, and so does not require conduit to meet code for commercial buildings (the wire can be run in the same raceway as communications cable, such as for a telephone or PA system, which reduces installation costs). The extra expense of the transformer could make a low-voltage system less cost-effective for small installations. However, higher voltage doesn’t lose as much over long wire runs (in larger, sprawling buildings). Most of the information presented here focuses on the 120v version.
» SET 100-001 (etc) GRC master manual, incl. service information for master and secondary clocks, circa-1970
(pdf, 35pg, 2.57mb)
Originally posted as image files on the NAWCC Chapter 52 website; assembled into printable format by me. (note: On letter-size paper, set “page scaling” to “none” so that your printer will slice off the dirty margins.)
» SET bulletin 525A, type GR “metal cased” master clock operating instructions, February 1956
(pdf, 4pg, 684kb)
» SET 108-448 GRC secondary drive motor conversion kit instructions, April 1968
(pdf, 2pg, 98.9kb)
(note: right-click, Save As… to download files directly)
I would really like to have a copy of a manual similar to the first one, only from about 1958~60 (showing the secondary movement with Ingraham Z drive motors and 12-hour correction). I am also interested in any other paperwork regarding GRC systems.
Starting in the postwar period, all SET movements in no.1 size were commonly mounted in the FMT/RMT modular metal cases. The FMT (flush-mount) and RMT (surface-mount; rim-mount) cases came in 10-, 12-, and 16-inch round models, and 10- and 12-inch square models. (I have not seen the square version made before late-1950s, or an art-deco dial or stepped hands in 16-inch size. I have only seen RMT-16 made by Johnson. FMT-12 is the most common case, certainly; and RMT-SQ-10 is the most rare case, in my opinion.)
The following seven types of secondary movements were commonly available in the modular FMT/RMT cases at certain times: AR3 (original AR type), AR2 and AR2A, and GR and GRC (120v and 24vac). These are the only types of no.1 secondary movements known to have been mass-produced by the original Standard Electric Time Company in the postwar period. Stand-alone synchronous movements were also offered in these cases.
Shown below is a size comparison of FMT cases of circa-1960 design (random selection) fitted with GRC movements.
The FMT case requires a special backbox (a type of conduit junction box) with specifically-spaced hanging brackets (examples of which are shown on the SET FMT backboxes and accessories page). The original aluminum brackets have a certain iconic look by themselves, in my opinion. There are two sizes of backbox: the smaller FMT-10 (and all Johnson FMT) size, and the taller FMT-12/16 size. Normal FMT cases were also used in double-sided brackets.
As far as I know, the GRC movement was only ever made in the no.1 size. (Traditionally, an 18-inch dial is the smallest that requires a no.2 movement.) The existence of dials larger than 16-inch or any outdoor dials has not been confirmed in buildings originally fitted with a GRC system. I refuse to believe such buildings did not ever exist, and would love to know how it was accomplished. Have you seen such an installation?
The type GR(C) only changed subtly over the years. However, as we all know, it’s often the minor details that go unnoticed by most people that cause the most problems. I’ve tried to keep track of the parts-shifting changes that I have noticed, and those are presented below. Note that there is often very little backing for these “facts” (such as “witness accounts” and things that turn up on eBay). If you know the actual truth about any of these things (or have facts that would fit in here, including things you may have seen), I would love to know about it. This chart will be updated as new information becomes available.
» US Patent #2662367, issued December 15, 1953 to George L. Riggs Jr. of SET (the owner’s son), showing specifically what became the bronze ratchet spring clips and ratchet pawl correction assembly that are a central part of the GR(C) movement. (Note that the shape of the movement plates in the patent drawings is rather similar to the Simplex dual-motor movement. It seems that all production GR movement plates were always the iconic rounded-square shape.)
» Very first GR secondary units assembled with existing art-deco dial and newer “necktie” hands. (It is unknown if SET ever pressed the GR minute collar onto a stepped hand, but an example of such would likely be most rare.)
» Very first GR masters assembled in “cutting-board master” case—the plain gray-painted case with a square art-deco dial and a vertical column of pushbuttons set into the cutting-board-like wooden front panel—before being replaced by the modern “steel-case master” of the ubiquitous design.
» The GR system has only hourly correction, no 12-hour correction.
1955-04-29 (possibly 1956, rather)
» Ingraham Z drive motor, Cramer 112 reset motor
» second hand with bent center (possibly sourced from Ingraham)
» early rough-printed modern dial (see note 01)
end(?) of GR system
» When GRC introduced, the “ACCUMULATOR” stamp began being used to mark GR units without 12-hour correction.
» GR “accumulator” made through at least 1961—long enough to be originally fitted with a Synchron drive motor.
» (I have only seen loose FMT-10 “accumulator” units; purpose/usage of system unknown. Anyone actually seen a whole system?)
1958: introduction of GRC system
» The GRC, originally marked with “ANTI-SCATTER” stamp indicating the presence of 12-hour correction (mechanism added to front of secondary movement), was introduced 1957 to early-1958. The following also occurred along the same time:
» usual sharp-printed international-modern dial introduced (see note 01)
» flat second hand introduced (see note 02)
» Cramer 117 reset motor used, rather than Cramer 112 motor (120v version)
(all by June 1958, see #7)
» reset motor changed to Synchron 640 (by Dec 1958, 120v version, see #4)
» “ANTI-SCATTER” changed to “Flexchron” stamp (between Jan and May, see #17 and #2)
» drive motor changed to Synchron 610 (after September 1960 but before July 1961; see note 03 and note 04)
» thin steel back plate (with bent tabs holding bezel clips in place) introduced, replacing thick shiny zinc plate with speed-clips (between January and July 1962)
» reset motor changed to Haydon, later to similar Standard-branded unit (see note 05)
» brass movement plates replaced with other materials, starting circa-1963 (same form, but no Ingraham Z oiling holes; materials incl. zinc, aluminum)
» rounded-tip second hand introduced (see note 02)
» movement plates made of aluminum; brass bushing added for seconds shaft
» brass weight added to nylon reset ratchet pawl
» wire clip moved to back of movement
» 6-pin Molex connector introduced
» modular RMT case with separate rim (same back plate as FMT) introduced
(all by June 1967, see #10 and #15)
» movement spacing pillar relocated (see note 06)
» mounting holes for CA-1 buzzer deleted (?)
» Johnson dial options added (stock option called “Tempo”)
» Johnson movement modifications introduced (see note 07)
» “Flexchron” stamp no longer used
» all no.1 FMT back plates made to fit in 10-inch backbox
» all no.1 movements (incl. AR) use GRC-sized black plastic clip-on dustcover
(all by 1971, see #3 and #11)
To view individual examples of GRC secondary clocks of all kinds, see the GRC examples page. To view a GRC secondary movement disassembled, along with notes about adjustment and operation, see the GRC from the inside page.
The original “rough-print” modern dial (with no logo border) was exactly that—more roughly printed than the later industrial/international-modern dial (with logo border; used 1957 to 1969). The difference doesn’t photograph very well, but it is very noticeable in-person. I keep an example of the original printing in my bedroom (see #6), as I believe it is easier to read in dim lighting—likely because all the markings are slightly bolder than the newer version.
The first composite image above compares the “bent-center” second hand (#6; 1955) and the center of the normal “cut-off” second hand (#4; 1958). The flat “cut-off” second hand was used from about 1957 to about 1965, and never seemed to stay exactly the same length. It seems likely that they were formed and painted with the tips attached to some kind of bracket, then each one was cut off. The margin of error doesn’t seem to have been controlled very well, in any event. The second composite image compares the tips of the different second hands, left to right: “bent-center” (#6; 1955), normal flat “cut-off” (#4; 1958; the longest example I have seen), and the “rounded-tip” version (1967; used about 1965+). It is important to note that the “bent-center” type is the only one that is the correct length to match the minute hand, in terms of proper aesthetics.
It is unknown to me exactly when the 24vac version was introduced. Bulletin 525A seems to suggest that a 24vac version was not available as of February 1956. The 24vac option was available as of mid-1959. Before 1961, the 24vac version also used the Ingraham Z drive motor. Other than the motors being made to operate at a different voltage, the 24vac and 120vac movements are identical.
Note that the operating speed of a “synchronous timing motor” (technically: a shaded-pole induction motor packaged with gearbox) is determined by the frequency of the power source. The stator coils are wound differently for the different voltages; the rotor and gearbox parts would be different for a different frequency (I do not know of GRCs being fitted with other than 60Hz motors of those two voltages, for installation in USA and Canada). If you “plug in” a 24v motor, it may run normally for a short time before the coil burns out (the outside case may not have time to get hot), at which point the motor will die.
The initial drive gears in the movement were changed to fit the 1rpm Synchron motor (the Ingraham Z is 8rpm). Specifically: the gears have fewer larger teeth (causing the movement to have a sloppy low-quality feel, in my opinion), the new idler gear was moved from the back plate to the motor mounting plate, and the seconds drive gear is also different. The thick spacer on the seconds shaft against the back plate was also deleted.
Shown above are dustcovers from (left to right): 1957 FMT-12 (#7), 1958 FMT-12 (#4), and 1963 RMT-12 (#8). The aluminum dustcover with the small (1-1/2-inch diameter) circular logo stamp belongs to movements with Ingraham Z drive motors, while the later type with the larger (2-1/16-inch diameter) stamp belongs to movements with Synchron drive motors. Both types state “THE STANDARD ELECTRIC TIME CO.” “SPRINGFIELD, MASS.” around the edge with the following in the middle of the smaller ones:
TYPE GR C
VOLTS: 120 CYCLES: 60
AMPS: .034 NORMAL DRIVE
.044 RESET DRIVE
The following appears on the larger ones:
VOLTS: 120 CYCLES: 60
DRIVE MOTOR 5 WATTS MAX.
RESET MOTOR 5 WATTS MAX.
The space after TYPE is filled with a separate stamp indicating case model, e.g. “FMT-12”. Note that the stamp used until (and shortly after) the introduction of 12-hour correction only said “GR”, while the later ones say “GR C”.
The examples of 24vac covers that I have seen use the same stamp, except with the “120” marked out, as shown above-left (#21; 1962 FMT-10 24vac). Above-right is a 1959 FMT-16 120v (#17) to complete the set of examples. The Johnson-era plastic covers only have the company name and “SECONDARY CLOCK”, with a printed paper sticker detailing the type of movement.
For some reason, they started using a Haydon reset motor (with the smaller case) in the early-1960s. At some point, the same motor appeared with the “Standard” brand stamped on it (I do not know if they actually made it).
Note that all reset motors are 60rpm and of the same mounting type, and are therefore interchangeable. Personally, I prefer the original gold-colored Synchron 640 reset motors to all others.
According to the newer 100-001 manual, the rightmost (viewed from rear) movement spacing pillar was relocated in February 1968. In the original movement, it is necessary to insert a certain size rod between the movement plates in order to line up the reset ratchet pawl arm (otherwise known as “the infamous #31 drill bit adjustment”). In the newer movement, the rightmost pillar is positioned where the drill bit would otherwise be during that adjustment, so the ratchet pawl arm should rest lightly on the pillar when properly adjusted.
The 108-448 conversion kit (designed to replace an Ingraham Z with a new Synchron drive motor), to which the instructions are provided above, included an “adjustment pillar” which connected only to the new back plate. The similar repair kit that was available before 1968 used the original back plate, with the idler gear shaft punched out. note 07
Nearly all of the new aspects of the Johnson movement simply cut costs, while making it harder to service (though I don’t think that is really a surprise to anyone). The most notable of these modifications is the “infamous little nylon spacer clip” (that’s the G-rated version of my derogatory name for it, anyway)—which replaced the formerly screwed-down metal (later nylon) spacer that holds the minute gears in place while the movement is partially disassembled. It is almost impossible to do anything with a Johnson movement without having to readjust the 12-hour correction, on account of that spacer being loose. If you ever have the chance to take one of these movements apart—don’t. I warned you. They did save two screws and two standoffs, though. Most of the gears are also thinner, to save metal. The completely unnecessary manual setting instructions are stamped into the back plate, to save the trouble of a printed paper sticker. The movement plates were already cheap aluminum, forget about brass. And the dustcover changed from aluminum to plastic, to save two screws and some aluminum. However, they did switch back to Synchron 640 reset motors (for a while). I assume most of these details persist to this day, in the movements made by ATS, but I have never had the pleasure(?) of rebuilding a newer one.
The following video shows the normal hourly correction of a GRC secondary as controlled by a Lathem LTR-series microprocessor-based master clock.