Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
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.
Zenith Farm Model 6V 27, 6-Tube Superhet Receiver Radio
Service Data Sheet
Zenith Farm Model 6V 27, 6-Tube Superhet. Receiver Radio
Service Data Sheet
(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 227 Radio Service Data Sheets as of
December 28, 2020.
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