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 is another Radio Service Data Sheet that appeared
in the May 1936 edition of Radio-Craft magazine. I post this schematic and functional description of
the Philco Models 39 and 39A, 6-Tube Dual-Range Battery Superhet manufacturers' publications for the
benefit of hobbyists and archivists who might be searching for such information either in a effort to
restore a radio to working condition, or to collect archival information.
Philco Models 39 and 39A, 6-Tube Dual-Range Battery Superhet
(Ranges, 550 to 1,720 kc., 5,500 to 16,000 kc.; class B output; A.V.C.; low battery drain; dynamic
speaker.)
Voltages in this set are as follows:
These readings are taken with a high-resistance voltmeter, and all are measured to ground.
The model 39 is operated from a 2-V. storage cell, while the model 39A is operated from a dry "A"
battery, and requires the use of a type 6 ballast tube, V7. The socket for V7 is also on the 39 chassis.
but is shorted out with a jumper.
The power consumption is 19 ma. from the high-voltage supply, and 670 ma. from the filament supply.
An output meter is needed for alignment and is connected to the plate terminal of V6. Locations of
all trimmers are shown in the detail drawing, with the exception of C6, which is located on the underside
of the chassis. The I.F. is aligned with the dial of the receiver set at 600, and the lead from the
service oscillator connected to the cap of V1. the regular grid-cap connection having been removed.
With the service oscillator still set at 460 kc., and the leads connected to the antenna and ground
terminals of the receiver. adjust the wavetrap condenser, C5, for minimum response. The alignment frequencies
for the broadcast band are 1,500 kc. and 600 kc,
For short-wave trimming, the maker recommends the use of a special, "crystal"-type service oscillator
which has a frequency of 3.6 mc. With the wave-band switch turned to the right, and the crystal oscillator
connected to the antenna and ground posts of the receiver, the 4th harmonic of the service oscillator
should be picked up at about halfway between 14 and 15 mc. on the receiver dial. With the dial at a
little more than 7 mc. the 2nd harmonic of the crystal service oscillator will be picked up. and at
this point C3 is adjusted for best response. Although an ordinary service oscillator without the crystal
feature may be used on the short-wave bands, the results are not so accurate.
A detail of the battery plug is given on the main diagram. It should be noted that the "A" leads
do not come out of this plug, but are brought out of the cable separately just above it. This plug is
made for connection directly to the special "B" and "C" battery unit, no connection wires being needed.
A special, low-drain pilot lamp is used.
Posted May 18, 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.
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 typing up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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