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About RF Cafe
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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 Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
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April 1936 Radio-Craft[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Radio-Craft was published from 1929 through 1953. All copyrights are hereby acknowledged. See all articles from Radio-Craft.
This Radio Service Data Sheet covers the Zenith Farm Model 6V 27, 6-tube superheterodyne receiver. Of particular interest here is an included wind-powered electricity generator meant to supply power in a rural location that was not yet serviced by electrical utility lines. The Rural Electrification Act had been signed into law a year earlier, but many years would pass before a majority of remote farms received power lines. Most - if not all - electronics servicemen had subscriptions to these magazines because they were a ready source of not just these service sheets, but because of the extensive articles offering advice on servicing radios and televisions. In fact, many electronics manufacturers had a policy of supplying service data only to bona fide shops. A large list is included at the bottom of the page of similar documents from vintage receiver schematics, troubleshooting tips, and alignment procedures. They were originally published in magazines like Radio-Craft, Radio and Television News, Radio News, etc. I scan and post them for the benefit of hobbyists who restore and service vintage electronics equipment.
(Low-drain tubes; class B output; bands: 550-1,780, 2,100-6,800, and 7,000-23,000 kc.; designed for 6 V. input and Zenith Wincharger.)
Voltages for this set are as follows:
"Oscillator C.-G. runs at - 1 V., plate at 150 V. **Voltages same for each section of tube V6.
All voltages are measured from socket contacts to ground with a 1,000-ohm-per-volt meter. Note that the filament is not a simple series connection, due to the fact that tubes with different filament voltage ratings are used together. No rectifier tube is needed, since a synchronous vibrator is employed.
Alignment procedure is as follows:
1-Attach service oscillator to control-grid cap of V2 and adjust trimmer condensers on I.F.T. 1 and I.F.T. 2 for highest output.
2-Place band switch in "A" or standard broadcast position and attach service oscillator to antenna and ground posts. Set service oscillator at 1,400 kc. and adjust trimmers "A," "B" and "C" as shown on chassis drawing for best output.
3-Set service oscillator at 600 kc. and rock dial indicator of receiver over 600 kc. on dial while adjusting broadcast padder "D."
4-Repeat both the above processes (2 and 3) to make certain of correct setting.
5-Place band switch in "B" position and set white pointer on 6 mc. Set service oscillator at 6 mc. and trim condenser "E" for highest output, while rocking dial pointer of receiver slowly over the 6 mc. division of the band.
6-Place band switch in "C" position and set dial at 18 mc. Adjust trimmer "F" to resonance while rocking receiver tuning condenser slowly over the 18 mc. division of the scale.
7-Set dial and service oscillator at 9 mc. and twist or untwist tinned bare wire loop (on front section of band switch under chassis ) for highest output.
8-Align broadcast band "A" again by adjusting trimmer "A" only. Repeat all operations for highest possible accuracy.
All testing of this set should be done with a 6 V. battery. Note that the input leads to the set are polarized and must be connected in the proper manner to produce reception. If replacement is necessary, be certain to use the correct type of vibrator, as any other will give poor or no results.
Above, a view of the general chassis layout, with tube and trimmer locations indicated.
Since this outfit is intended for use on farms or any other isolated location where commercial power is not available, it is necessary to use some other type of power to charge the 6 V. storage battery employed. The needed power is furnished by the Zenith Wineharger," an automatic windmill device, which keeps the battery in a charged condition. An assembly drawing of this instrument is given, from which its construction may be seen. The charger should be oiled and greased once a month. The generator cover must be removed in order to gain access to the rear bearing, and the terminal posts. If the generator causes interference in the receiver on the short-wave bands, a special switching arrangement is supplied by the makers which will allow the generator to run without harm although it is not charging. It should be noted that the generator will be damaged if allowed to run when it is not connected or not charging, unless the above mentioned switching arrangement is used.
The necessary connections to the battery and controls are made from the charging panel, a drawing of which is shown. The meter thereon will indicate the rate of charge or discharge of the battery. If repairs have been made to the generator or panel it is best to test these units for correct operation before they are put in use. This can be easily done by connecting a short piece of copper wire between the upper and lower connections or leads of the relay. This shorts the relay and makes the charging generator act as a motor, which will revolve the propeller and cause the meter to show a discharge of about 4 A. This is a positive check of connections in the circuit. The same connection may be made if the machine is new and stiff or if the lubricant is cold, to start it turning.
No connections are shown to the receiver from the battery in the diagram of charger connections. The receiver is simply connected directly across the battery, care being taken to observe the proper polarity. Wire no smaller than No. 6 B & S gauge should be used for this purpose. Wire from charger to battery should be No.8, up to 50 ft.; No. 6 up to 100 ft.; No. 4 up to 200 ft.
Posted June 17, 2015
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 185 Radio Service Data Sheets as of April 12, 2017.