Virtual Museum of Vintage Electronic Counters
This is a unique collection of early test instruments of the type known as electronic counters (or frequency counters). These 1950s instruments implemented digital circuits using vacuum tubes, and since this requires many tubes (and also many related components, and an adequate power supply), the instruments were large, heavy, and expensive (the equivalent of $5,000 to $40,000, perhaps, in today's US dollars, depending on model). Moreover, while other test instruments had also simpler versions, which were perfectly useful and reliable at less than one tenth the cost, there was little that could be simplified in counters to reduce their cost.
As a result, few counters were built compared with other instruments (fewer than a hundred for some models, and just a few thousand for the popular models). Also, because of their large size, most of them were discarded once retired. They were displaced by transistorized counters starting in early 1960s, having dominated this field, thus, for only about ten years. (It must be noted that some tube counters were already using solid-
This museum is an attempt to preserve and to explain visually that brief period in the history of digital electronics. At the same time, it serves as an illustration of complex 1950s electronic hardware in general.
There are 37 models, representing several manufacturers, and depicted with hundreds of high-
Basic principles of the early counters
The name "counter" derives from the fact that these instruments count the number of transitions (level changes) in the input signal. The transitions are converted to pulses, which trigger the counting circuits.
An internal time-
Since the accuracy of all measurements is determined ultimately by the precision of the original time-
If the input signal is a regular waveform, its transitions indicate cycles, and the instrument will measure the signal's frequency (usually as cycles/second — what we call today Hertz, or Hz). But the signal can represent many other phenomena, so the transitions are generally known as events. (Thus, Beckman called these measurements Events Per Unit Time, or EPUT, or E/UT.)
Many counters can measure time intervals. This function is implemented by reversing the input and the time-
A related function is to measure the ratio of two frequencies. The pulses of the lower-
The check function lets the operator test the counter without any input signals. The time-
Some counters have decimal points — small lamps situated between the display digits and lit according to the position of the selection knobs. They help the operator interpret the number of pulses in familiar units (Hz or KHz or MHz for frequency, sec or msec or µsec for time).
The counter can be instructed to repeat a measurement. The operator can do it by pressing the reset button, or by limiting the display time: after displaying the result for a brief period defined by the operator, the counter resets itself, performs the measurement, and returns to the display step, repeating this cycle indefinitely. For regular waveforms, the values repeatedly displayed should be identical, or very close.
Decade counters
The counting operation in most counters is performed by plug-
Decade counters are connected in series, the output of the first module to the input of the second one (which is on its left in the instrument's front panel), and so on, for as many digits as the counter requires. Watching the displayed count, each digit starts at 0 and increases by 1 every time the one on its right changes from 9 back to 0. At any moment, therefore, the value displayed is the number of input pulses since the counter was last reset. In most applications, though, the first few digits change too fast to follow, and it is only the final measurement that matters.
Most decade counters have 4 tubes, each one consisting of 2 triodes in a circuit that can be in one of two states, like 0 and 1. These states are flipped by the input pulses. The tube generates an output pulse when its state returns to 0, at every second input pulse. Each tube drives the next one, dividing the pulse frequency by 2 and at the same time doubling the number of states possible for the module as a whole. In digital terms, each tube is one bit, and the 4 tubes are one hexadecimal digit with 16 states, 0000 to 1111. The input pulses cause the tubes to display these states in binary sequence, and then return to 0000. But 6 states (in the middle of the sequence) are skipped electronically, so the module is reduced to the 10 states needed for a decimal digit.
In some counters the decade counter for the first (and sometimes also the second) digit is more complex than the others, because it must support the highest frequency (the following ones receive lower and lower frequencies). In 10 MHz counters, the circuit for the first (and sometimes also the second) digit is so complex that it requires a separate section, and only a small display module is placed in the front panel. Conversely, in some simple counters the frequency is reduced even by the first decade counters to 10 - 15 Hz, so the following digits can be implemented with a small mechanical register.
In addition to counting, the decade counter displays the decimal digit corresponding to the current state, 0 - 9. A decoding circuit translates the 4 bits into 10 output voltages, which light 10 neon lamps arranged in a column behind a mask with digit-
Starting in 1959, the display tubes known as Nixie were used as an alternative display method. These gas-
List of counters
Museum instructions
• The counters are listed by model number within manufacturer.
• In the list of counters, hover with the mouse in the top left corner of a thumbnail picture to display a larger image. Click on a picture or on the model number to go to the counter's views window. The list of views is displayed there as thumbnails in the left pane, while the selected pictures are displayed in the right pane. Under each thumbnail view there are 3 buttons, S M L (Small, Medium, Large), which let you select the picture size. With Medium and Large you can see smaller details. (You may be able to further enlarge details with the browser's zoom feature Ctrl +.) The button you select stays black until you click another one, to help you find the current view if you scroll the views list up or down.
• If the browser's window is large enough, Small fits in its entirety. Medium and Large are 2.5x and 6.4x larger than Small, and they must be scrolled in order to bring the portion of interest in the window. Scroll the image directly with the mouse, or using the scrollbars, similarly to scrolling a map. The browser will generate scrollbars for Small too if the window is not large enough to display it in full. But then you will have two sets of scrollbars for Medium and Large, which can be confusing.
• Click Back to list at top or bottom to return to the list of counters.
• Click Gallery for a quick scan of all views, forward or backward (in Small size).
• Click Add tab to open a second views window, where you can select other views. This lets you compare views by clicking on the tabs or by flipping them with the browser's feature Ctrl Tab. More than two tabs can be opened, by clicking Add tab in any one of the open tabs. To compare views from two or more different counters, click Add tab and then Back to list, where you can select another counter.
Note: The pictures are licensed under the Creative Commons Attribution-
Hewlett-Packard Company (HP)
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• Counts events • Measures frequency • Input signal to 120 KHz • Optional crystal time-
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• Counts events • Measures frequency • Input signal to 120 KHz • Includes crystal time-
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• Rack-
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• Counts events • Measures frequency • Input signal to 120 KHz • Optional crystal time-
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• Rack-
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• Counts events • Measures frequency • Input signal to 120 KHz • Includes crystal time-
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• Counts events • Measures frequency • Input signal to 1.2 MHz • Shown with crystal time-
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• Same model number for cabinet and rack-
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HP 522B Electronic Counter (early version)
• Early version of model 522B; see that model for details • Differences: front panel appearance, chassis appearance, decade counters (Beckman), plug-
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• Counts events • Measures frequency, period, time interval • Input signal to 1.2 MHz • 64 tubes • 6‑digit display with Nixie decade counters; 5 decimal points • This unit includes the Digital Recorder option (which drives a printer) • Width/
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• Rack-
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• Counts events • Measures frequency, period, time interval • Input signal to 1.2 MHz • 63 tubes • 6‑digit display with columnar decade counters; 5 decimal points • Width/
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• Rack-
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• Precursor of models 524C and 524D • Same model number for cabinet and rack-
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• Same model number for cabinet and rack-
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• Same model number for cabinet and rack-
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• Alternative model # AN/USM‑26 • Military version of model 524B rack-
Beckman Instruments - Berkeley Division
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• Measures frequency • Input signal to 100 KHz • 45 tubes • 5‑digit display with columnar decade counters • Width/
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Beckman 5001 Electronic Counter
• Counts events • Input signal to 125 pulses/
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Beckman 5230 Universal EPUT and Timer
• Counts events • Measures frequency, period, time interval, frequencies ratio • Input signal to 100 KHz • 31 tubes • 4‑digit display with columnar decade counters • Width/
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Beckman 5500 Universal Counter and Timer
• Counts events • Measures frequency, period, time interval • Input signal to 100 KHz • 50 tubes • 5‑digit display with columnar decade counters; 6 decimal points • Width/
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• Counter and heterodyne frequency converter in one cabinet • Counts events • Measures frequency, period, time interval, frequencies ratio • Input signal to 2.1 MHz (to 42 MHz using the converter) • 64 tubes (excluding the converter) • 7‑digit display with columnar decade counters • Width/
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• Measures frequency • Input signal to 100 KHz • Uses subminiature tubes and dense design to attain a very small size • 36 tubes • 5‑digit display with small columnar decade counters • Width/
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Beckman 7350A Universal EPUT and Timer
• Counts events • Measures frequency, period, time interval, frequencies ratio • Input signal to 500 KHz • 46 tubes • 6‑digit display with columnar decade counters • Width/
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Beckman 7360A Universal EPUT and Timer
• Counts events • Measures frequency, period, time interval, frequencies ratio • Input signal to 2 MHz • 57 tubes • 7‑digit display with columnar decade counters • Width/
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Beckman 7360R Universal EPUT and Timer
• Rack-
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Beckman 8361LT Preset Universal EPUT and Timer
• Counts events • Measures frequency, period, time interval, frequencies ratio • Option to divide or multiply the measured entity by a preset value • Input signal to 1 MHz • 66 tubes • 6‑digit electroluminescent display panel with 7‑segment figures, driven by separate decade counters using optical conversion logic • 4‑digit preset count, selected with thumbwheels and implemented with 4 special decade counters • Width/
Computer Measurements Company (CMC)
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• Counts events • Measures frequency • Input signal to 220 KHz • 36 tubes • 4‑digit display with columnar decade counters • Width/
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CMC 201C Frequency Period Counter
• Counts events • Measures frequency, period • Input signal to 220 KHz • 41 tubes • 5‑digit display with columnar decade counters • Width/
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CMC 225B Universal Counter-Timer
• Counts events • Measures frequency, period, time interval, frequencies ratio • Input signal to 220 KHz • 56 tubes • 5‑digit display with columnar decade counters; 4 decimal points • Width/
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CMC 225C Universal Counter-Timer
• Counts events • Measures frequency, period, time interval, frequencies ratio • Input signal to 220 KHz • 54 tubes • 5‑digit display with columnar decade counters; 3 decimal points • Width/
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• Counts events • Input signal to 15,000 pulses/
Sentinel Electronics
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Sentinel FR-114A/U Frequency Meter
• Alternative model # AN/TSM‑16 • Made for the U.S. military • Counts events • Measures frequency, period, time interval • Input signal to 1 MHz • 39 tubes • 6‑digit display with Nixie tubes, driven by separate decade counters using beam switching tubes • Width/
General Radio Company
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General Radio 1130-A Digital Time and Frequency Meter
• One model for both bench and rack use • Counts events • Measures frequency, period, time interval • Input signal to 10 MHz • Optional external plug-
Hamner Electronics Co.
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• Counts events up to a preset number, or up to a preset time length if used with the N‑803 timer (see that model for details) • Input signal to 1 MHz • 43 tubes • 7‑digit display with columnar decade counters • Designed with a very low profile for minimal vertical space in a rack • Width/
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• Used with the N‑277 scaler (see that model for details) to preset a time length, or to measure the time elapsed, for the events counted by the scaler • 40 tubes • 6‑digit display with columnar decade counters • Designed with a very low profile for minimal vertical space in a rack • Width/
Potter Instrument Company
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• Counts events • Measures time interval • 26 tubes • 3‑digit columnar display with separate decade counters; 3 decimal points • Most circuits implemented as plug-