Radio Engineering Labs. 648B Schematic

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Product Information:
Model:648B
Manufacturer:Radio Engineering Labs.

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Page 1:

Mounts 6 6B
RbL MODLLS ?h?s 6t7B AND 6H8B FM BROADCASI RECEIVERS
These receivers are single superheterodyne units of orthodox circuit and
design As with all VHF receiving equipment, performance is dependent on
correct installation, particularly the associated antenna and lead in
system
Both 70 and 300 ohm lines may be used here without serious mismatch con
sequences whether or not the ground terminal (marked G) is used depends
on local conditions Because of uncertainties LD this connection and be
cause the inout circuit coupling is fairly tight, tne latter is not pre
cisely tracked at the factory For very weak signals or for technical use
at any one frequency, this circuit may be trimmed by adjusting Cl This
is accessible at the top of the chassis and is located as shown in the tube
layout sketch
For convenience in tuning and rough measuring the circuits are adyusted so
that one small division of the TUNE meter corresponds to a frequency snift
of about 2O kilocycles, and so that the steps o the RF GAIN control are
roughly ten to one each Indications on the SI NAL meter are approximately
linear Both these meters may be supplemented externally by use of the
connections on the rear terminal board The TUNE meter is 25 O 25 micro
amperes, and the SIGNAL is O l milliampere
To use external meters, remove the strap between terminals and 5 and the
ground bus from terminal 5, then connect the TUNE meter between terminals
5 and l (ground) and the SIGNAL meter between terminal M and 1 If only
one of these meters are connected externally, the terminal for the second
meter must be connected to terminal 1
Terminals are provided for connecting an external signal to the audio am-
plifier input and selecting this signal by means of the switch on the
Terminal 2,is high and terminal l is ground These termin-
als represent an AC impedance of about one megohm and 30 micro-microfarads
For the ?t?s about 2v. Rus input is required for full audio amplifier out-
front panel
The 6h6B and 6h7B receivers are designed for operation at ll5 volts. The
should not be operated permanently on lines higher than 125 volts. The 6K8
receiver requires at least 5.8 volts DC at the indicated terminals. They
\are connected for negative ground. If the vehicle has a positive ground
system the vibrators must be reoriented according to the legend on the top
of the Vibrapacks.
The maximum audio output of the 6h6B receiver is ten watts into either 500
or 8 ohms (mismatch up to 2 to l here is not generally aurally serious).
The maximum output of the 6h7B receiver is + 18 DBM into 600 or 150 ohms.
This receiver is connected for 600 ohm load; to use with 150 ohm load the
output transformer should be restrapped by replacing strap from 5 U0 6 by
a strap from A to 6 and another from 5 to 7. The maximum audio output of
the 6hBB receiver is h watts into 6 ohms.
The nominal impedance at the antenna terminals (marked A - A) is 150 ohms.
"John F. Rider

Page 2:

PAGE 20-2 RADIO ENGINEERING LABS.
MODELS EUR>I,L6B,
| CHASSIS TUBE AND TRIIMBUIH LAYOUT
Auouo a ?owER Sum
(C)John F. Rider

Page 3:

RADIO ENGINEERING LABS. PAGE 20-3
__ MODELS 64613,
(C)John F. Rider

Page 4:

0
PAGE 20-6 RAD|0 Ej\|GINEE_l?_|NG LABS. ___ ____
MODEL 6L|.8B
(C)John F. Rider

Page 5:

RADIO E GIN RING LABS PAG
MODELS ?t?
SYMBOL SYMBOL
REF DESCRIPTION REF DESCRIPTION
Not used
Not used
Same as C
Not used
Same as Cl
Same as C
Same as C
Same as C1
Same as C3
Same as C11
Not used
Same As C18
Same as C
Same as C18
Same as C6
Same as C18
Capa?it?r, slass, variable I Pilot 11ght, miniature
bayonet base, 6 8 volts,
15 amps
Same as Il
Antenna and first grid
Coil assembly
Not used
Not used
Fixer grid coil
Oscillator coil
Not used
Same as L8
Signal strength meter, 0 1 ma
Tuning meter, 25 O 25 microamps
1 watt
1 2 watt
1 2 watt
1 2 watt
1 2 watt
1 watt
1 2 watt
1 2 watt
1 2 watt
1 2 watt
1 2 watt
1/2 watt
1/2 watt
Same as R8
150 ohms i10%,
/`\ MODEL 6h6B, CQYB and 6#8B FM RECEIVER PARTS LIST F02 RF AND IF CHASSIS
C7 Not used L6
0 John F. Rider

Page 6:

':. I 1 RADIO E x _l 1. S.
MODELS 213163,
MODEL 644613, 611713 and 6L18B FM Hmm PARTS LIST F011 RF AND IF 0HAss1s(c0NT~D>
SYMBOL SYMBOL Q
REF. DESCRIPTION REF. DESQ?lBTION
R15 Same as R10 Vg)
R16 Resistor, 100,000 ohms, V5) Same as V3
_-31032, 1/2 watt V5)
_R18 Same as R10
R19 Resistor, 100,000 ohms, V8 Type 7A6 tube
~ f_10%, 1 watt
R20 Resistor, u7,000 Ohms X1 Socket, octal, mica filled
+1O%' 1 watt Bakelite
i10%, 1/2 watt X )
R23 Resistor, 66,000 ohms, XS) Sam as X1
R25 Same as R20
R26 Rssisusr, 33,000 ohms, X9 I'lini8buI'?, bayonet typ'
50%, 1/2 watt S??k?*=
R27 Same as R26 X10)
R28 Resistor, 070,000 ohms, xll) Sam SS X9
g_10%, 1/2 watt X12)
+1O%, 1/2 watt Z1 Interstage coupling unit,
R30 Same as R9 10-7 mc'
Z2 Interstage coupling unit,
Sl Not used 10-7 m?~
S2 sw1u?h,>>nsp, 3 pole, 11 Z3 Same as Z1
positign Zi; Interstage coupling unit, ID.
S3 Switch, single pole, 10-7 1110-
single throw, rotary Z5 Interstage coupling unit,
V1 Type 7F'8 tube 10.7 mc.
V2 same as V1 Z6 Discriminator assembly
V3 Type TAG? tube unit, 10.7 mc.
MODEL 611613 COMBINED AUDIO as Powlan SUPPLY CHASSIS \
SYMBOL SYMBOL
REF. DESCRIPTION REF. DESCRIPTION
C10 Same as C102 C109 Capacitor, fixed, elec-
Cl0 Same as C101 trolytic, 10 mfd., L75
C10 Same as C101 VDCW
C106 Capacitor, fixed, dry C110 Capacitor, fixed, mica \_/
o John F. Rider

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