Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
Many months have passed since
I last posted one of the Radio Service Data Sheets for vintage radio sets. This
one for the Sentinel Model 217−P portable appeared in the August 1940 issue
of Radio−Craft magazine. Hobbyists and professional electronics service
shops relied on these back in the day because obtaining the information from manufacturers
could be difficult or even impossible. Some companies would not provide service
information for alignment and troubleshooting to businesses that were not officially
endorsed to do so. That left some of the smaller shops and most do-it-yourselfers
without a means to work on sets. Once places like
SAMS Photofacts
came along with information packets that could be purchased by anyone, the need
for these magazine-based data sheets was lessened. I provide them now because in
many cases the are once again the only source available.
Sentinel Model 217-P Portable Radio Set Radio Service Data Sheet
6-Tube Superhet.: A.C.-D.C. and Battery
Operation: Automatic Volume Control: Built-In Loop Antenna: Sliderule-Type Dial:
Underwriters Approved: Broadcast Band (Range 535 to 1,730 kc.): Inclined-Panel Leather
Case Stage of R.F. Amplification: 5-10. P.M. Dynamic Loudspeaker.
Alignment Procedure
Remove chassis from cabinet. Place loop antenna in the same position it would
be when the chassis is in the cabinet.
I.F. Stages
Set receiver dial to any point where no interference signal is received. Feed
a 455-kc. signal from the test oscillator to the grid cap of the 1A7GT tube through
a 0.2-mf. dummy antenna condenser. Do not remove the grid cap. Adjust each of the
2nd I.F. transformer trimmers for maximum output and each of the 1st I.F. transformer
trimmers for maximum output. (See diagram showing locations of trimmers.)
1,730 TO 540 kc. Band
When adjusting the 1,730 kc. oscillator trimmer and the 1,400 kc. antenna trimmer,
do not connect the test oscillator directly to the loop. Instead, couple the test
oscillator to receiver loop by making a loop consisting of 5 to 10 turns of No.
20 to 30 size wire wound on a 3-in. form and attached across the output of the test
oscillator. Place this test oscillator loop near the set loop and be sure that neither
moves while aligning.
Set the receiver dial to exactly 1,730 kc. and feed a 1,730 kc. signal to the
loop antenna of the receiver. Adjust the 1,730 kc. oscillator trimmer for maximum
output. Then set the receiver dial to approximately 1,400 kc. Feed a 1,400 kc. test
signal into the receiver loop antenna and adjust the loop trimmer for maximum output,
rocking the gang condenser throughout this operation.
Note that this portable, unlike most portables, incorporates a stage of R.F.
amplification. When an external aerial is used a good ground connection must be
made.
Sentinel model 217-P 3-way portable radio set.
Posted June 12, 2019
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
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