Hewlett Packard 113BR, 103AR, and 724BR - a Clock and Frequency Standard system

1960 Vintage Analog Clock with 5 parts in 10¹⁰ per day
Better than 5 parts in 10¹⁰ averaged over 1-second intervals

This specimen was rescued from an SK estate and had not been used in years. The 113BR section was the highest item mounted in the open-top rack, therefore it has years of dust on it while the two other units are fairly clean. There should be a partial enclosure for the 113BR, which incidentally makes it fully rack mountable, but the enclosure is missing. No cables came with the gear, but fortunately the entire system between the power supply, oscillator, and clock appears to operate from a single negative 24VDC source. The DC power consumption is only 22-30VDC @ 290mA (7 Watts), so it's very 'green' for the size, weight, and vintage. The dust came off the transparent cover of the clock mechanism easily with a damp cloth so it may not be too difficult to clean it up with some care to avoid disturbing the electronics. No manuals came with the instruments. On this specimen, the 1KC Auxiliary Output BNC connector on the front panel has been damaged.

Some Basics and Thoughts:

The 113BR clock and Divider appears to operate from a negative 24VDC supply, and requires a 100KC input as the reference/frequency drive. Time is presented on a dual scale 24 Hour dial. A stepping motor is mounted via an annular bearing aligned with its separately rotating shaft axis. Its frame rotation is limited in either direction by a movement-absorbing, dampened spring (the damper, if that is what is seen, appears to look reddish inside the spring in the photos). The motor drives the clock gears thereby the hands, via a springy coupling so that the quick stepped-rotation of its shaft is converted to smoother movement of the same rotation degrees and direction. The above describes an electromechanical integrator. It is truly a work of art. The 113BR also provides outputs of 100CPS, 10KC, 1KC, and one-second "TICK" pulse. The TIME REFERENCE control allows +/- 500us adjustment per turn, and a 1000 turns counter has a 9999 ms range. The 113BR has a built-in CIRCUIT CHECK meter. The h/p catalog contains more information.

The 103AR Quartz Oscillator is the heart of the timekeeping system and responsible for the 5 parts in 10¹⁰ overall stability. It uses a special oven within an oven to keep the crystal at a constant temperature. The ovens are linked together in a feedback system to maintain the highest possible stability for the crystal's environment. An electromechanical digital indicator reads directly in parts per 10¹⁰. Outputs of 5MC, 1MC, and 100KC are provided on the front panel. Screwdriver adjustments are povided with Coarse and Fine ranges of 1.5 parts in 10⁶ and 600 parts in 10¹⁰, respectively. The 103AR also has a built-in CIRCUIT CHECK meter. This specimen apparently has option H08, as indicated on the front panel, but it looks the same as 103AR photos found on the www except for the additional front-panel output of "5MC with extreme spectral purity" (harmonics >80dB below rated output), normally found only on the 104AR which cost $750 more in 1960. The h/p catalog contains more information.
radiomuseum.org has h/p 103AR schematics available.

The 724BR power supply operates from 120VAC and originally included a 'large' bank of NiCd cells which would power the system for up to 2 days in absence of commercial 120V power. About 60 of the 75 Lbs (34Kg) quoted for the power supply's weight was accounted for by the NiCd cells. The charger took about a week to top them off in order to get the 2-day backup service from them.

An experimenter could substitute a 10,000uF electrolytic capacitor as a filter in the spirit of temporary playfulness, though a 100AH (minimum) @ 24V battery would restore the unit to specification in regard to a 48-hour backup endurance.

An alternative to the NiCd, possibly allowing the original charger/supply to be retained, could be made from LTO (Lithium Titanate) cells, which are among the safest Li-based battery cells. This chemistry has a 2.40V nominal VPC with a 1.8V cutoff (compare to two NiCd cells in series for a 2.4V nominal voltage and a 2.2V discharge cutoff). Substitution of the 2400Wh battery's 38Wh/kg NiCd cells with 50Wh/kg LTO cells could reduce the battery wight by at least 24%

The power 724BR charger/supply is specified to be overload-proof. All caveats apply when considering substitution of one cell type with another. The 724BR has a DC voltmeter and a zero-center DC ammeter showing battery charge and discharge. The h/p catalog contains more information.