Electrical Research Lab 7700 Schematic

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Manufacturer:Electrical Research Lab (Sentinal)(ERLA)

Schematics Content:

Please note: this content is a computer-generated interpretation of the above schematic and is provided only to help assist you in locating this schematic. For the actual text, please consult the schematic above. Thank you.

Page 1:


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Sentinel Social' Layouls

Below will be found socket layouts for
several Sentinel receivers. It is sug-
gested that they be cur out and pasted

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on the respective pages of the Rider'r
Mantra/r indicated. The schematic dia-
grams of the sets appears on the follow-
ing pages: 560, page 3-3 and 2117 in
the Rider-Combination; 550, page 5-9,'
603, page 5-17,' 6200, page 5-34,"4300,
page 5-24; 5500, page 5-25 ,' 7700, page
5-35,' 1040, page 5-21; 660 Ballery,
page 5-19,' and 1020-11, page 4-15.
Erlu Model 6200

The O_OZ-rnf. condenser, Part No.`
9714, used to bypass the grid return of
the First i-f. transformer was a 0.01-mf.
condenser in early production. To
eliminate any tendency of the i-f. arn-
plifrer to oscillate, the 0.01-mf. con-
denser has been changed to 0.02 mf. in
later production. If receivers are encoun-
tered in which i-f. oscillation occurs,
replace the 0.01-ml. condenser, if there
is one, with one having a value of

The 10,000-ohm resistor, Part No.
6786, and the 0.005-mf. condenser, Part
No. 1275, have been added no the plate
circuit of the 35 output tube, where
they are in series with the plate and
ground. This addition improves the
tone quality and decreases background
noise. Excessive background noise and
high-pitched tone in these sets can be
rectified by adding these two compon-
ents as indicated. Early production sets
did not have this resistor and condenser.

The 4-mf. wet electrolytic condenser,
Part No. 129i, connected between
ground and the connection between

the primary of the first i-f. transformer
and the 10,000-ohm resistor in the No.
2 grid circuit or' the 1A6 tube, has been
added in late production sets to elimi-
nate motorboating when the set is op-
_erated with __low "B" battery voltages.
If sets are encountered that mototboat
when the "B" battery is low, install a

The complete servicing data on this
receiver will be published in Volume

Eric Models 7700, 7732, 774|

In early production of these sets the
value of the condenser in the grid re-
turn of the first i-f. transformer was
.01 mf., Part No. 7860. To eliminate
tendency of the i-f. amplifier to oscil-
late, this condenser has been changed
to .02 mf., Part No. 9714. If any
receivers are found having i-f. oscilla-
tions, change the .01 mf. condenser to
one having a value of .02 mf.

To eliminate self modulation of the
1C6 tube the 50,000-ohm resistor, Part
Nc. 6879, has beenrchanged to 35,000-
ohm resistor, Part No, 1618. Wher-
ever self modulation occurs, try another
1C6 tube or replace the 50,000-ohrn re-
sistor with one having a value of

Sentinel |08

The voltage and alignment data for
Model 108 will be found herewith. The
schematic diagram for this receiver ap-
pears on Sentinel page 1-3 of Ilie 'fe-
vired edition af Ride/.r Volume I ,' page
*624-11 of tba early edition and on page
2107 of the Rider-Combination Manual.

Type tion ment Plate Gridscfeen Flute MA

245 Output 2.4 250 50" _ .
280 Reet. 4.85 27 per plate
't computqu _ ' ; m une volume applied.
** To tulle 245 bus '113, read between the elev-

Alignment Data:

Set the signal generator to 175 kc.
and connect the output to the grid of the
224, lst detector, from which the grid
cap has been removed. Trimmers of the
i-f. transformers are accessible through
the small holes in the top of the cans.
Align the grid trimmer of the first i-f.
coil, then the second i-f. coil.

Replace the grid cap on the lst de-
tector and connect the signal generators
output to the antenna and ground posts
of the set, having tuned it to 1435 kc.

Set the receiver's dial to this frequency
also. Track the variable condenseis by
adjusting the trimmers in the following
order; Oscillator, antenna and r-f. (The
sections of the condenser are in this Y,
orderhstarting at the front of the set.)
Then check the condensers at 1295 kc.,
by bending the end plate of the rotors.
Check also at S80, 650, and 550 ltc.

Eric Model 9100

Some or' the early Model 9100 rel
ceivers had a tendency to rnotorbuut un
the broadcast band when the tone con-
trol was turned to the bass position. This`
has been rectified in later production
by removing the O_OOZ-mf. condenser,
Part No. 6590, and by passing the plate
of each 30 a-t'. tube with a 0.004-mr',
condenser to the chassis base. Make this
change if motorbuating should be
encountered in any Model 9100 receiver.

International 53, 553

The hrst production of these models,
in which a 617 tube is used as the sec-
ond detector, does not incorporate AVC.
When operated in the vicinity of pow-
erful .broadcast stations, a tendency to-
ward overloading may be found on
strong signals, It is evidenced by block-
ing out of the signals as the volume con-
trol is advanced. This condition can be
corrected by making the simple change
shown in the accompanying illustration.

Partial schematic diagram of nrly Mod-Is
53. 553 Showing changes lo prevsnl bleclt-

` Originally th'e grid returns of the 6K7

and the 617 tubes go directly to ground.
See schematic diagram in Ride/.r Vol-
ume VI, page 6-8. These should be re-
moved from ground, tied together and
tenuned to ground through a 1-megohm
resistor sh'unted by a condenser of 0.01,-
rnf. or larger. In making this change,
be sure that the cathode of the 617 tube
is connected as shown in the illustration
and not left connected to the low end of
the second i-f, transformer grid wind-

(C)John F. Rider, Publisher

Page 3:


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