Early
Digital Test
Equipment
Systron Donner 1037-5
Counter
 

Manufacturer: Systron Donner
Model: 1037-5
Year: 1967
Schematic: RE
 
Max. Rate: 50 MHz
Display: NIXIE
Digits: 8
Logic: discrete transistor, TTL

From the outside this counter appears to be a fairly standard higher-end NIXIE-display model of the period. Examination of the internals reveals it to be a tour of the unusual semiconductor devices that were developed in the 1960s.

2 unijunction transistors are used, one to generate the display delay, the other as an oscillator to trigger display updates.

Silicon-Controlled-Switches are used in each decade as a combination latch and driver for the biquinary NIXIE tubes. This achieved the storage function without requiring a full set of flip-flops to duplicate the counter flip-flops.

Tunnel diodes are used in the first decade to achieve the high (50MHz) count frequency. The decade begins with a 5-stage Johnson counter. Each stage uses a tunnel diode and discrete transistor to make a 'flip-flop'. This counter is double-clocked (somehow) by each input pulse so only 5 of the 10 states are effectively used. The Johnson counter drives a conventional two-transistor flip-flop to complete the 10 states for the decade. The 5 outputs from the Johnson counter and the output from the flip-flop go on to drive a decoder and Silicon-Controlled-Switch latch and thence on to the NIXIE tube.

Curiously, the timebase divider string is made from seven 7490 TTL decade counters, date-coded from 1966 and 1967. The SSI 7400 series had been introduced a couple of years earlier but this is quite early for these MSI devices.


From top, the first board contains an input amplifier and the 50MHz tunnel diode ring counter. Next is a 250KC decade counter/decoder/driver. At bottom is the timebase divider string containing the early 7490 ICs.

A closer view of the 50MHz tunnel diode ring counter of the first decade, with the components arranged in a .. ring!



- Unit Log -

Serial Number: 916
Year of Manufacture: 1967 (ICs stamped with 66xx and 67xx)
Date of Receipt: 2005 Jun 26
State upon Receipt: Reasonably clean but fairly banged up. Non-functional. Double digits in display.


Date: 2005 Jun
Procedure: Nixie anode voltage too high (280V). Both transistors in HV regulator shorted. HV pass transistor swapped with one from unit 919. HV driver transistor on board replaced.


Date: 2005 Jun
Procedure: V-6 supply low. Corrosion on associated fuse contacts. Fuse replaced.


Date: 2005 Jun
Procedure: Input board swapped with unit 919.


Date: 2005 Jul 17
Procedure: 50MC readout board swapped with unit 919.


Date: 2005 Jul 17
Procedure: One 250KC board swapped with unit 919.


Date: 2005 Jul 17
Procedure: Bulb in '*' lamp replaced with bulb from a type 387 bulb.


Date: 2005 Jul 17
Procedure: DP lamp units -3 and -7 replaced.


Date: 2005 Jul 19
Procedure: Cleaned. Screws and washers on back panel replaced. Reassembled. Fully functional.



- Unit Log -

Serial Number: 919
Year of Manufacture: ??
Date of Receipt: 2005 Jun 26
State upon Receipt: Reasonably clean but fairly banged up. Original internal crystal oscillator in oven had been removed and replaced with a 1MHz plug-in oscillator.


Date: 2005 Jun
Procedure: HV pass transistor swapped to unit 916. Pass transistor replaced.


Date: 2005 Jun
Procedure: Input board swapped with unit 916.


Date: 2005 Jun
Procedure: Unit will count but there is no automatic gate cycling. Connector on back has internal connections. Removed. OK.


Date: 2005 Jun
Procedure: One 250KC counter board does not count. 390pF trigger capacitor in first flip-flop replaced. OK.


Date: 2005 Jun
Procedure: Bulb in lamp for 4th decimal point from right replaced with surplus grain-of-wheat bulb.


Date: 2005 Jul 12
Procedure: Three coax wires resoldered on function switch.


Date: 2005 Jul 13
Procedure: Count mode does not function because replacement internal 1MHz oscillator was wired directly to the 'external time base' input, and does not trigger the gate in count mode. 1MHz oscillator output rewired to more properly mimic the original internal oscillator. Count mode now functions.


Date: 2005 Jul 13
Procedure: Bulb in 'KHz' lamp replaced with bulb from a type 387 bulb.


Date: 2005 Oct
Procedure: Silkscreened plastic sheet for labels over units lamps touched up with black paint.


Date: 2005 Oct 17
Procedure: Broken pin on V+30 pass transistor socket, lead soldered to transistor. Reassembled.


Date: 2005 Oct 20
Procedure: For 5-10 minutes after turn-on, GATE lamp does not turn off completely and storage mode does not function properly (occasional updates to the display occur during the gate period).
Otherwise fully functional.
TO DO: Replacement HV pass transistor is TO-220 case hacked onto a TO-3 case. Should be replaced with a proper transistor in a TO-3 case.



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Early Digital Test Equipment
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