Hewlett-Packard 524B
1957
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Hewlett-Packard 524B
1957
| Max. Rate: | 10 MHz |
| Digits: | 8 |
| Display: | 1-of-10 neon, analog meters |
| Logic: | tube |
| Schematic: | RE |
| More Photos: | Yes |
The HP524 was a remarkable instrument in it's day with it's high count rate. This is the 'B' version. It utilises 84 vacuum tubes, physically is approximately a cube of 19-inch rack-width (~ 4 cubic feet), weighs in at 110 to 120 pounds and consumes 600 watts of power. In the 1950s this is what was required to count to just 10MHz!
The photo shows the unit displaying a count of "647852.84".
While this particular unit required days of cleaning after I received it, it had remarkably little wrong with it electronically. One tube, two capacitors and one resistor solved the electronic problems.
Note: To adjust units- and tens-digit meters: with MODE=MANUAL GATE, PERIOD UNIT=100KC, GATE=OPEN, adjust CENTER pots for both meters to bring needle to dot between 4 & 5. Set GATE=CLOSED, press RESET, now adjust ZERO pots.
Note: Fan must be operating when chassis is in cabinet. If not, thermal cutout may trip after a few minutes.
For more about the 524 models see the HP 520 Series.
Philips PW4032
1959 ?
| Max. Rate: | ~ 62 KHz (visual observation) |
| Digits: | 5 |
| Display: | E1T counter tubes |
| Logic: | tube, E1T counter tubes |
| Schematic: | RE |
| More Photos: | Yes |
This counter is notable for it's use of the E1T counter tubes.
Functionally this unit is just an event counter, it does not include an internal timebase.
Hewlett-Packard 521C
1960
| Max. Rate: | 120 KHz |
| Digits: | 5 |
| Display: | 1-of-10 neon |
| Logic: | tube |
| Schematic: | MF |
| More Photos: | Yes |
One of the models from HP's 520 series. There are 44 vacuum tubes in this model.
This unit was made in 1960 but the model actually dates from the mid-50's.
Hewlett-Packard 524C
1961
| Max. Rate: | 10 MHz |
| Digits: | 8 |
| Display: | NIXIE |
| Logic: | tube |
| Schematic: | RE,MF |
| More Photos: | Yes |
The 'C' version of the HP 524. The 524C uses NIXIE tubes for the display instead of the 1-of-10 neon-bulb displays of the other 524 versions. The unit I have was manufactured in 1961, however the schematics in the 524C/D manual are dated 1959, making this a quite early instrument to use NIXIEs.
The 1962 HP catalog presents a list price of $2400.
The photo shows a unit with a 525A 100MC Frequency Converter plugged into the front panel.
This unit had an exasperating fault which caused the count to reset to zero immediately at the end of the gate period. One would watch it speed through the count and then have no opportunity to observe the result. After tracking the problem to a subtle issue around the gate circuitry, the unit is fully functional.
For more about the 524 models see the HP 520 Series.
Transistor Specialties Inc. Apti-Meter 361
1961
| Max. Rate: | 1.3 MHz (measured) |
| Digits: | 6 |
| Display: | NIXIE |
| Logic: | discrete transistor Ge-PNP |
| Schematic: | RE |
| More Photos: | Yes |
An instrument from a smaller manufacturer but very well built.
RACAL SA.520
1963
| Max. Rate: | 300 KHz |
| Digits: | 4 |
| Display: | 1-of-10 incand. |
| Logic: | discrete transistor Ge-PNP |
| Schematic: | RE |
| More Photos: | Yes |
A simple, low-speed model from the British radio manufacturer.
While only 4 digits are displayed it is possible to get 6 digits of precision
by taking a reading on each of the 3 provided gate periods.
Northeastern 40-80
1964
| Max. Rate: | 30 MHz (measured) |
| Digits: | 8 |
| Display: | NIXIE |
| Logic: | discrete transistor Ge-PNP |
| Schematic: | RE |
| More Photos: | Yes |
Rugged well-built unit, sealed circuit boards.
The unit in the photo includes a 200 MHz pre-scaler plug-in (right side).
Venner TSA 3336/2
1964
| Max. Rate: | 1.1 MHz |
| Digits: | 6 |
| Display: | meter projection |
| Logic: | discrete transistor Ge-PNP |
| Schematic: | RE,MF |
| More Photos: | Yes |
A discrete transistor counter made in England in the early 1960's.
This model uses film-projection displays. The display brightness is uneven across the digits because portions of the films have darkened with age.
(Advertisement: Wireless World, Dec 1961, page 22.)
| Max. Rate: | 12.5 MHz |
| Digits: | 7 |
| Display: | NIXIE |
| Logic: | TTL |
| Schematic: | RE |
An early all-IC counter. The main ICs used in this counter are MSI TTL decade counters and NIXIE drivers. They are proprietary HP devices having some additional functionality not found in the standard 7490 / 7441 devices.
The additional functionality of the ICs is for leading-zero blanking in the display. The decade counter ICs have an 11th state (decimal 15) to represent blanked-zero. The NIXIE driver IC blanks the NIXIE upon input of 15. Upon reset the decade counters are set to the blanked-zero state. Any clock activity on a given decade (digit) unblanks that decade. At the end of the gate/count period leading zeroes are still blanked while lower-order zeroes have been unblanked. This scheme can result in some briefly idiosyncratic displays when changing the function mode.
Unfortunately the special ICs seem to fail somewhat frequently, especially the NIXIE drivers,
making it difficult to keep units of this model or series functional.
| Max. Rate: | 5 KHz |
| Digits: | 4 |
| Display: | dekatron |
| Logic: | tube |
| Schematic: | RE |
| More Photos: | Yes |
A small timer and event counter. The timebase is a small synchronous motor spinning a disc with holes in it, and an optical sensor. Does not measure frequency directly as there is no gate control.
The 6802 dekatron tubes are specified to a maximum rate of 5KHz, by simple visual observation the counter appears to function up to around 6 KHz.
The photo exposure shows the unit actively counting.
The LSD (digit at bottom) has passed through zero,
the consequent carry resulting in the increment of the digit above.
Para-Time Instruments Inc. 130
1967
| Max. Rate: | > 90 KHz (measured) |
| Digits: | 4 |
| Display: | dekatron |
| Logic: | tube, transistor, RTL |
| Schematic: | RE |
| More Photos: | Yes |
A nice little dekatron-based counter.
This model is notable for it's combination of old and new technologies. The counters/display are dekatron tubes. Dual-triode tubes are used for the inter-digit dekatron drivers. RTL integrated circuits make up the timebase and control logic, and a few discrete transistors interface between the RTL and the tubes.
Two types of dekatron counter tubes are used.
The first two digits (LSD) use high-speed type 6909 dekatrons,
while the remaining digits use 6802 dekatrons.
The 6802's have the orange glow typical of neon while the 6909's have a purplish-pink glow.
Other than that, their physical appearance and internal construction appear identical.
A tube manual indicates the 6802's are good to 5KHz while 6909's should count up to 100KHz.
This unit seems to count reliably to over 90KHz.
| Max. Rate: | 50 MHz |
| Digits: | 8 |
| Display: | NIXIE |
| Logic: | discrete transistor, TTL |
| Schematic: | RE |
| More Photos: | Yes |
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.
Monsanto 110A
1968
| Max. Rate: | 85 MHz? |
| Digits: | 7 |
| Display: | NIXIE |
| Logic: | RTL, ECL |
| Schematic: | RE |
| More Photos: | Yes |
The maximum count rate on this unit needs to be measured.
The first decade uses ECL flip-flops (MC1013) which are specified to 85 MHz.
However, the second decade is labeled as "12.5 MHz",
which would suggest the first decade is good to 125 MHz.
Whether or not the rest of the input circuitry keeps up with either of
these possibilities is unknown.
Heathkit IB-1100
1972
| Max. Rate: | 30 MHz |
| Digits: | 5 |
| Display: | NIXIE |
| Logic: | TTL |
| Schematic: | RE, MF |
An early entry into the lower end of the counter market, as inexpensive ICs became available.
Based on standard 7400 TTL - 7490, 7475, 7441 counter string.
Very simple from the user interface side (frequency only) but note the reasonably
high count rate compared to far more expensive counters from just a few years earlier.
Ballantine Laboratories Inc. Autometronic 5500B
1975
| Max. Rate: | 80 - 125 MHz (IC spec) |
| Digits: | 8 |
| Display: | 7-seg LED |
| Logic: | TTL |
| Schematic: | RE |
A novel counter with auto-ranging.
Rather than selecting the gate time, the operator selects the desired number of
digits of resolution.
The counter adjusts the display over the sampling cycle to fit that resolution.
Fluke 1900A
1976
| Max. Rate: | 80 MHz |
| Digits: | 6 |
| Display: | LED |
| Logic: | TTL, CMOS, MSI |
| Schematic: | MF |
| More Photos: | Yes |
Counter with Auto-ranging feature.
Hewlett-Packard 3440A / 3445A plug-in
1965
| Functions: | DCV, ACV |
| Digits: | 4 |
| Display: | NIXIE |
| Logic: | Ge-PNP |
| Schematic: | RE |
| More Photos: | Yes |
An early digital voltmeter utilising a conversion technique no longer popular. A ramp is generated spanning a positive and negative voltage range. A gate controlling the clock input to the counter string is tripped at the input level on the ramp and at zero. Which trip comes last determines the polarity indication.
The shortcoming of this technique is that the accuracy of the displayed result is dependant upon both the slope of the ramp and the frequency of the oscillator feeding the counter. They must be mutually stable to maintain accuracy, however they are implemented as independant electronic units. The test switch and adjustment on the front panel provide for tweaking the slope of the ramp to bring it into consistency with the count frequency.
Early use of FETs around the input stage.
The 3445A plug-in provides a fairly quick auto-ranging capability.
| Functions: | DCV |
| Digits: | 3 |
| Display: | NIXIE |
| Logic: | discrete transistor Si/Ge-PNP/NPN |
| Schematic: | RE |
| More Photos: | Yes |
A conventional design for the A/D converter using a staircase ramp.
The staircase is generated by a D/A converter fed by the counter circuits and
is compared with the input level to control the clocking of the counter.
Honeywell / Schneider Digitest 500
1969
| Functions: | DCV, ACV, Ohms |
| Digits: | 3 |
| Display: | NIXIE |
| Logic: | discrete transistor, LSI |
| Schematic: | RE |
| More Photos: | Yes |
A funny little VOM built into a calculator-style case. The matrix organisation for the function/range selection is novel.
This is actually a Schneider product made in France, re-badged for sale under the Honeywell name. The model was also sold under the Schneider name. The Schneider units seem to be more prevalent, at least in Europe, based on web searches.
A single IC contains most of the digital portion of the electronics - the counters and display multiplexing circuitry - a fairly high level of integration for the time. A single 709 op-amp is also present, the rest of the circuitry is discrete, albeit with several special multiple-resistor ceramic modules.
The unit can be operated from both the AC mains or an external 12 VDC supply (tip negative on the DC barrel connector).
The AC mains supply can be configured for 100 to 240VAC, the selection being made by solder connections on the bottom of the main circuit board.
Weston 1294
1970
| Functions: | DCV |
| Digits: | 4.5 |
| Display: | NIXIE |
| Logic: | TTL |
| Schematic: | RE |
| More Photos: | Yes |
Industrial panel meters made the transition from analog to digital in the early 1970's. This is one of the few NIXIE-display models produced before such instruments settled in to the use of LEDs for display.
The A-to-D converter is of the dual-slope integration type, implemented with discrete and SSI components. The design impressively achieves this with a relative paucity of components, and packed into a small form factor.
The native range of the design is +/- 200.0 mV, auto-polarity is included.
Model options allowed for internal input configurations for other voltage and current ranges.
Overflow is indicated by a flashing of the display.
Weston 1240
1972
| Functions: | DCV, DCmA, Ohms, ACV, ACmA |
| Digits: | 3.5 |
| Display: | NIXIE |
| Logic: | RTL, Fairchild CµL |
| Schematic: | (see comment) |
| More Photos: | Yes |
Benchtop DMM from Weston. This unit was manufactured in 1972, however the model is likely from around 1969-70. The model has auto-polarity but not auto-ranging.
Fairchild CµL (Counter Micrologic) is used for the counter string. CµL was a small series of RTL-class MSI devices introduced by Fairchild in the mid-1960s intended specifically for decade counter-displays. The series is comprised of 4 IC types:
The Heathkit IM-102 uses an essentially identical circuit design,
the IM-102 appears to have been a copy of this Weston model.
Weston 4440
1972
| Functions: | DCV, ACV, 200uA-DC/AC, Ohms |
| Digits: | 3.5 |
| Display: | LED |
| Logic: | LSI digital, discrete & SSI analog |
| Schematic: | MF |
| More Photos: | Yes |
Early battery-powered portable DVM.
To operate without batteries, connect 5.5-6V power supply to pins at rear,
+ on smaller right pin, - on larger left pin, as viewed from rear.
Heathkit IM-102
1973
| Functions: | DCV, DCmA, Ohms, ACV, ACmA |
| Digits: | 3.5 |
| Display: | NIXIE |
| Logic: | RTL, Fairchild CµL |
| Schematic: | MF |
Based on the circuit design, this appears to be a copy of the Weston 1240.
Heathkit IM-1202
1973
| Functions: | DCV, ACV, Ohms, DCA, ACA |
| Digits: | 2.5 |
| Display: | NIXIE |
| Logic: | discrete transistor, TTL |
| Schematic: | MF,RE |
A basic low-budget digital multimeter from the early 1970s. The digital logic portion of this instrument uses standard TTL ICs but the A/D converter is built from discrete components.
No auto-polarity or auto-ranging.
Sold for CDN$ 89.95 in kit form in 1974.
Fluke 8100B
1973 (1969)
| Functions: | DCV, ACV, Ohms |
| Digits: | 4 |
| Display: | NIXIE |
| Logic: | DTL,TTL |
| Schematic: | MF |
| More Photos: | Yes |
This model is based on another novel A-D conversion technique called "Recirculating-Remainder A-D Conversion" by Fluke.
The technique can be described as performing long division with analog values. A counter, resistive D-A ladder and comparator are arranged in a typical staircase A-D loop but this arrangement is only 4 bits wide: only enough for one decade of resolution. The process starts by using this single-digit A-D converter to resolve the most significant digit. The analog difference between the input value and the D-A ladder (the remainder) is stored in a sample-and-hold circuit, multiplied by 10 through an op amp, and fed to the single-digit A-D converter to resolve the second digit. The process is then repeated to resolve the 3rd and 4th digits.
This results in a minimal component count on the digital side with only 3 digital ICs: a 4-bit counter, a NIXIE decoder/driver and a triple NAND gate. On the analog side numerous JFETs are used as analog switches.
This model has auto-polarity but not auto-ranging.
Fluke 8000A
1974
| Functions: | DCV, ACV, DCA, ACA, Ohms |
| Digits: | 3.5 |
| Display: | LED |
| Logic: | MSI, TTL |
| Schematic: | MF |
| More Photos: | Yes |
Popular high-end digital multi-meter from the late 1970s, in bench-top form.
| Functions: | DCV, ACV, DCA, ACA, Ohms, Auto-range |
| Digits: | 3.5 |
| Display: | LED |
| Logic: | LSI |
| Schematic: | - |
| More Photos: | Yes |
Nice bench-top digital multimeter. Auto-ranging.
B & K 2810
1977
| Functions: | DCV, ACV, DCA, ACA, Ohms |
| Digits: | 3.5 |
| Display: | LED |
| Logic: | LSI digital, discrete & SSI analog |
| Schematic: | RE partial |
| More Photos: | Yes |
Basic battery-powered portable DVM.
To operate without batteries, apply 5-6VDC tip+ to rear jack.
Fluke 8030A
1980
| Functions: | DCV, ACV, DCmA, ACmA, Ohms |
| Digits: | 3 1/2 |
| Display: | LED |
| Logic: | LSI |
| Schematic: | MF |
| More Photos: | Yes |
Kind of a compacted version of the Fluke 8000A, this model is based around the same two proprietary Fluke ICs, SC522 and SC523.
While these units are built for the most part with the customary quality of Fluke instruments
they do have a significant flaw in the flexi-print strips used to connect the printed circuit boards.
Failures of these strips have probably been the end of many of these units.
Hamner Electronics Nuclear Scaler
1966
| Functions: | Nuclear Scaler |
| Digits: | |
| Display: | 1-of-10 Incandescent |
| Logic: | Discrete Transistor |
| Schematic: | RE |
| More Photos: | Yes |
Hamner Electronics was a 1960s manufacturer of nuclear instrumentation, located in Princeton, New Jersey. This is a NIM bin populated with modules to form a nuclear scaler.
NIM (Nuclear Instrumentation Module) is a standard created in the late-1950s defining dimensions and requirements for a card cage (bin) accepting plug-in modules and backplane providing power to the modules.
The modules here are:
The spectrum stabiliser apparently interacts in a loop arrangement with the radiation source / experiment. A third level is established between the min-max levels of the window discriminator, thus defining two regions (over/under) within the window. Detected radiation-event pulses occurring within the two regions pump a charge-pump up or down. The output from the charge-pump is fed back to the experiment to perform some control function. The overall functional operation is much like a phase-locked-loop.
The gate is manually controlled by pushbuttons. Additionally, a 'preset' switch can select one of several decades upon which to automatically stop counting, e.g. close the gate after 1000 or 10,000, etc. pulses.
These modules are all held together in an:
with an:
The Scaler and Timer/Scaler are interconnected such that their respective start/stop gate-controls interact in synchronism. The idea then, is one can start an experiment by pressing Start, then have it stop automatically after some time period or upon reaching some event count. At the end, the respective variable number of events in a fixed period, or the variable time needed for a fixed number of events to occur, is presented.
Simple test procedure: Enable 60Hz TEST on scaler; TIMER, 0.1S and 10^2 PRESET on Timer.
After pressing START, activity should stop after 10S.
Displays should present Scaler=600, Timer=100.
Metrotech 4510
1972
| Functions: | 24-hour Clock, Audio Time-Code Generator |
| Digits: | 6 |
| Display: | RCA Numitron |
| Logic: | TTL |
| Schematic: | RE |
| More Photos: | Yes |
This is a time-code generator for use in audio tape logging systems, this unit was used for police call logging. Standalone, it functions as a 24-hour clock. The Metrotech 4520 is the associated decoder. These units also have Dictaphone and "Dictachron Time Code Unit" labelling on them.
For the time-code generation, time stamps are continually output in serial form as two binary levels amplitude-modulating a 300Hz audio tone. Each time stamp is a sequence of 25 bits: a start marker bit, a 0 bit, 5 BCD digits of 4 bits with the LSB of the unit-seconds first, 2 bits for the tens-of-hours digit, and a 1 bit. Each bit occupies 40mS. The 40mS is divided into thirds, the first third is always occupied by 4 cyles of 300Hz carrier to mark the start of the bit, the second third will be empty for a logic-0 and 300Hz carrier for a logic-1. The third third is used to indicate the beginning of a time stamp: normally it is empty, the presence of 300Hz carrier marks the start of the 25-bit sequence. At 40mS per bit and 25 bits, a time stamp occupies precisely 1 second.
The format, and decoder design, are such that a serial time stamp can be decoded when received in either direction, allowing the time stamps to be displayed during rewind of the tape.
Numitrons (RCA Part No. DR-2000) were a 7-segment incandescent display device produced by RCA starting around the late-1960s/1970, just prior to 7-segment LED displays. Numitrons were packaged in a vacuum-tube-style envelope with a standard 9-pin (Noval) base. While Numitrons - distinct from Minitrons or other 7-segment incandescent displays in flat packages - were well-enough known, this is one of the few pieces of production equipment I have seen that actually uses them.
Date codes in this unit and the companion decoder span the years from 1972 to 1980.
The use of Numitrons, original (not LS) SSI/MSI TTL, and the overall design suggest the design as being from the early 1970s.
The later time stamps were likely the result of maintenance over the service life of the units.
Metrotech 4520
1972
| Functions: | Audio Time-Code Decoder |
| Digits: | 6 |
| Display: | RCA Numitron |
| Logic: | TTL |
| Schematic: | - |
| More Photos: | Yes |
The decoder compatriot for the Metrotech 4510 time-code generator.
This unit simply receives the audio signal from tape, or directly from the generator, and displays the time stamp.
Sencore LC53
1980
| Functions: | C, L, leakage, ringing test |
| Digits: | 3.5 |
| Display: | LED |
| Logic: | CMOS |
| Schematic: | MF, redrawing |
| More Photos: | Yes |
The Sencor "Z" Meter measures capacitance and inductance. It also includes a leakage measurement for capacitors, performed at selectable operating voltages up to 600V; and a ringing test for inductors.
Note the test leads must be plugged into the BNC jack to zero the meter for small C measurement. The capacitance of the test leads is necessary to bring the zeroing into range.
The manufacturer schematic has been redrawn for clarity.
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Photo Gallery
Early Digital Test Equipment |
bhilpert Apr 2008 |
