HP 100E Frequency Standard
HP 101A 1 MC Oscillator

These two early frequency references have been recently added to the Time Frequency Instrument Collection.

The 100E was bought on ebay last month and the 101A is a donation.
One of the many contributions made by Jacques-Jean Tronca to the HP Memory Project.

Main characteristics of the instruments are:

• Both are introduced in the 1961 catalog.
• Both use the same 1MC Quartz Crystal Oven with temperature indicator on the front panel.
• The 100E is the last evolution of the HP 100 series frequency reference. It is the last, full vacuum tubes, frequency standard including many accessories like a timing comb generator and a built-in oscilloscope.
• The 101A is a low cost transistorized version, designed specifically to be the time base for various counters of the era like the 523C/D, the 524B or the 5275A Time Interval Counter.

HP 100E, Last Generation Vacuum Tube Wiring Style

The HP 100E is a typical example of the last generation of vacuum tubes technology chassis wiring at HP. By the end of the 60s most instruments will be transistorized and will be wired using printed circuit boards. Some exceptions to this rule will be made in very long life products like the 428B Clip-on DC Milliammeter. In 1986, the last production run of the 428B, still made of vacuum tubes, will be printed circuit board wired.

State of the Art Frequency Accuracy in 1960:

Both of these instruments use a 1 MC (Megahertz was called Megacycle in 1960) Quartz crystal enclosed in a temperature controlled oven.
The same time base was used in most HP frequency counter like the 524D (See "Early Electronic Frequency Counter" in the 1939-1960 period of the Quick Tour). The temperature controlled crystal oscillator was the state of the art in frequency stability and accuracy by the end of the 50s. This technology will soon make a considerable leap forward with the introduction of the first cesium beam atomic clock in 1964.

HP's achievement in time base performance is clearly illustrated by the article below. Published in the Hewlett Packard Journal volume 10, number 3-4. the article describes the long and complex process of quartz crystal adjustment and aging before it can be used in the high precision time base of HP instrument.

The Hewlett-Packard Application Note 200-2 is another fundamental reading about Quartz Crystals precision and stability when they are used as the controlling element of electronic oscillators. This document which is still today a reference, can be download in PDF format from here: "FUNDAMENTALS OF QUARTZ OSCILLATORS" (250 ko).

Before the HP 100E & HP 101A

The 100E is the last evolution of the HP 100 series frequency reference. Precise frequency reference was an obvious major requirement for an accurate calibration of the many signal generators produced at HP from the very beginning of the company.
Consequently, a frequency standard is already found among the 14 different model numbers, in the HP 1943, first catalog. The HP 100A is one of these instruments which was first designed for internal use and then commercialized because there was an obvious market need.

The two pages dedicated to the HP 100A in the 1943 catalog are shown below. (Full content of this catalog, and many others, can be downloaded in PDF format from the Glenn Robb "hparchive" Web Site.).

The Model 100B, First temperature Controlled Frequency Standard

The next evolution was the HP 100B introduced in the 1945 catalog. The main improvement resided in the addition of a temperature controlled oven for the 100 kHz Reference Quartz Crystal.

Last Step Before the 100E

The HP 100D was introduced in the 1950 catalog. The second edition of the Hewlett Packard Journal, October, 1949, will be fully dedicated to the Model 100D introduction and description.
A lower cost with slightly degraded performance version of the 100D, the HP 100C is also produced in 1950 as shown on the bottom photo of this page. It is the copy of a full page publicity made by HP is the "ELECTRONICS" Magazine, August 1950.