I did a little research into the history of Precision’s signal generators via the scans of “Service” magazine hosted by David Gleason’s AmericanRadioHistory.com.
The E-100
Precision’s earliest signal general was the E-100.
It was first mentioned in “Service” magazine in an ad in the June 1938 edition.
An ad in the September 1938 issue featured a photo of the E-100 in the lower left.
The November 1938 issue of “Service” magazine featured an article in their “Test Equipment” section introducing the Precision E-100 signal generator. The E-100 had a frequency range from 100 kilocycles to 15.0 megacycles.
The E-100 featured what Precision termed their “unit coil assembly” construction for the RF oscillator and bandswitch. “The coils, trimmers, all the resistors, etc., associated with them as well as the 6K8 r-f oscillator-buffer amplifier are mounted directly on the band switch.”
The E-200
Precision introduced their new 1940 line of test equipment in an ad in the June 1939 issue of “Service” magazine.
They first mentioned the E-200 in an ad in the October 1939 issue of “Service” magazine. The E-200 increased the frequency range over the E-100, from 110 kilocycles up to 72 megacycles. It was also advertised as
incorporating the new "Precision A.V.C. Substitution System” allowing for simplification of alignment problems of the modern receiver without interfering action of the A.V.C. circuit.
This interesting feature of the E-200 series signal generators is the provision of an AVC bias supply that enables you to disable the AVC by clamping the AVC line to a fixed voltage. This allows you to align the receiver at a typical AVC level rather than at maximum gain. Due to the Miller effect the effective grid capacitance of the IF tubes varies with the AVC-controlled gain. Consequently using an input signal below the AVC threshold results in a different IF alignment than one where the AVC line is at a more typical level. I think that whether the alignment is significantly different is up for debate.
The E-200 was shown again in an ad in the January 1940 issue of “Service” magazine.
Precision Apparatus Company Chief Engineer (and later Vice President of Engineering), G. N. Goldberger, published an article in the May 1940 issue of “Service” magazine entitled “Signal Substitution” that featured Precision's new E-200. In this article he argued that aligning at the appropriate AVC level was important to providing optimum performance, thus showing the value of the E-200’s "AVC Substitution System". His article is also a useful general overview of servicing by signal substitution, and a teaser for Precision’s upcoming “Servicing by Signal Substitution” book.
The article also included a schematic for the E-200.
The May 1940 issue of “Service” also featured a two-page ad spread from Precision, with a pre-publication announcement of their book "Servicing by Signal Substitution”. The ad touts that the E-200 “[u]ses the new 6SJ7 in the “PRECISION” developed “UNIT OSCILLATOR” – buffer amplifier construction, insuring MAXIMUM 1% DEVIATION ON ALL BANDS”.
The E-200-C
Precision suspended advertising in “Service” magazine during World War II. Presumably they didn’t have anything to sell to civilians during the war.
Precision reappears in the January 1946 issue in the New Products column with a blurb announcing their new EV-10-P VTVM. They resumed advertising in “Service” magazine in the June 1947 issue, with a general ad touting the quality of their gear.
The August 1947 issue of “Service” magazine included this article entitled “FM Alignment – Step-by-Step Analysis Using a 88-Kc to 120-Mc Signal Generator and a VTVM or a 20,000 Ohms-Per-Volt Multi-Range Meter”. The article was excerpted from Goldberger’s book “Service by Signal Substitution”. The article notes "Precision Apparatus Co. series E-200-C Signal Generator used in this step-by-step analysis”. The extended frequency range of the E-200-C enables it to be used with receivers for the new post-war FM band, unlike the earlier E-200.
The E-200-C makes its first advertising appearance in the November 1947 issue of “Service”.
The “Servicing by Signal Substitution” book also serves as a user manual for the E-200-C. It notes that the E-200-C continues the “Unit Oscillator” construction of its predecessors:
A 6SJ7 (see schematics) in the Precision-developed “UNIT-OSCILLATOR” construction provides shortest possible leads between oscillator and associated circuits are maintained. All components including coils, trimmers, condensers, socket, tube, resistors, etc., are actually mounted right onto the band switch, as illustrated in the picture on page (10).
High quality, ceramic spaced band switch, silver plated switch contacts, ceramic suspended trimmers, plus low drift, silver-mica high frequency loading condensers, in addition to the rugged “UNIT-OSCILLATOR” construction, insures 1% ACCURACY ON ALL BANDS under widely varying conditions. This permits use of Series E-200-C for complete F.M. receiver alignment as well as for TV. marker and other TV. applications.
E-200/E-200-C variations
The E-200-C continued in production well into the 1960’s, so of course there were many production changes over the years. It has a reputation of never matching the schematic in the manual.
This late version of the E-200-C (note the new styling) uses seven-pin miniature tubes, 6AU6 and 6U8, in place of the 6SJ7 and 6C5 used by the earlier versions. Very early E-200-C’s used four-pin type 80 rectifiers as did the earlier E-200, but later versions switched to the octal 5Y3.
Mike (NE5U) over on the Antique Radio Forum has compiled a set of schematics of several of the E-200/E-200-C variations, along with a spreadsheet of their component values. Mike has permitted me to host copies of them:
- Mike’s schematic compilation
- Mike’s parts spreadsheet