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Philco Model 200-X Radio Service Data Sheet
December 1934 Radio-Craft

December 1934 Radio-Craft

December 1934 Radio Craft Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

Philco Model 200-X (RadioMuseum.com) - RF Cafe

Philco Model 200−X (RadioMuseum.com)

In order to facilitate searches for information on vintage radios, I have been scanning and running OCR (optical character recognition) on many of the Radio Service Data Sheets like this one featuring the Philco Model 200−X, 10−tube high−fidelity superheterodyne model in graphical format. It appeared in the December 1934 issue of Radio−Craft magazine. A fine restored example of the Philco Model 200−X appears on the Radio Museum website. There are still many people who restore and service these vintage radios, and often it can be difficult or impossible to find schematics and/or tuning information. A running list of all data sheets can be found at the bottom of the page to facilitate a search. Here is another Philco Model 200−X on the PhilcoRadio.com website.

Philco Model 200−X Radio Service Data Sheet

Philco Model 200-X Radio Service Data Sheet, December 1934 Radio Craft - RF Cafe

This is the first commercial radio set designed for high-quality dual reception of standard 10 kc. broadcast stations, and the new 20 kc. "high-fidelity" stations just below 200 meters; a smoothly adjustable control varies the selectivity from "sharp" to "broad."

As the circuit of this receiver differs considerably from previous designs, a resume of its outstanding characteristics is essential to the Service Man, and of interest to the technician.

The selectivity afforded by stage V1 eliminates image frequency response and cross-modulation. Resistor R13, 10 ohms ("selectivity losser 'A'") broadens, to 15 k c. selectivity, the resonance of the first-detector tuned input circuit; resistor R15, 50 000 ohms ("selectivity losser 'B'", performs a similar function in the oscillator tuned input circuit.

Tertiary-(third) winding trap circuits L, of LF.T.'s 1 and 2, tuned EXACTLY to the carrier frequency clip the tops of the resonance peaks (leaving a double-peak characteristic) by absorbing some of the energy in the low- and middle-frequency register of the I.F.'s audio component - and thus accentuating the high-frequency register.

The degree of this absorption determines the selectivity of the circuit. and is a function of the degree of coupling between the primary and secondary windings of I.F.T.'s 1 and 2, as determined by the setting of the "fidelity-selectivity" control-resistors R24A and R24B ("selectivity controls 'A' and 'B'''), and R24C ("sensitivity compensator").

Without the resistance of R24A and R24B in the respective circuits the tertiary or trap windings L act as a heavy load across the respective secondary windings, which results in wide-band (decreased I.F. selectivity) reception and decreased sensitivity; the loss in sensitivity in this manner is then compensated simultaneously by an automatic increase in amplification. since the setting of the "fidelity selectivity" control decreases the amount of resistance effective in cathode resistor R24C, thus increasing the gain of tubes V2 and V3.

With the resistances of R24A and R24B in circuit the trap action is very slight, and circuit selectivity and sensitivity are greatly increased.



Posted August 11, 2022
(updated from original post on 9/19/2014)

Radio Service Data Sheets

These schematics, tuning instructions, and other data are reproduced from my collection of vintage radio and electronics magazines. As back in the era, similar schematic and service info was available for purchase from sources such as SAMS Photofacts, but these printings were a no-cost bonus for readers. There are 227 Radio Service Data Sheets as of December 28, 2020.

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RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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