Scott Radio Labs., Inc. 310 Schematic

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Manufacturer:Scott Radio Labs., Inc.

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Page 1:

iggn RADIO LAB R -

Power Input



Tuning Range


- Speaker



The Model 310 is a combination designed for the reception or radio
broadcast programs and for the reproduction of phonograph records,
television sound or other external sound.

the following separate pieces of equipment:
record changer, and (3) high fidelity speaker.

The receiver includes


105 Watts at 117 Volts, 50-60 cycles. (Phono

motor 60 cycles, 25 watts additional.)

Total 12 including two-rectifiers.

Superheterodyne with RF amplifier stage (three gang
tuning condenser) on all bands. Three stage FM-IF
amplification (10.7 mc). One stage AM-IF (455 kc).
Ratio detector on FM. Drift compensation on RF
section. Push-pull output with 6 db inverse feedback.
Sound input for phono and for TV or other external

10 watts (2-6VGGT tubes in push-pull). Less than
5% distortion at full output.

(Carrier modulated 30% at 400 cycles. Output 500

milliwatts with 10 db signal to noise ratio.)

Overall 50 to 20,000 cps plus or minus 1 db.
Separate bass and treble control. Phono input
equalized for elimination of objectionable scratch
level. AM and FM audio equalized to BC standards.

Hi-fidelity 12 inch PM. 8 ohm voice coil.


The Model 310 has the following tube complement:

Symbol Tube Application Symbol Tube Application

Vl GBAG RF Amplifier V7 6AL5 Ratio Detector, FM

V2 6BE6 Conv. & AM Osc. V8 6307 1st Audio Amplifier

V3 604 FM Oscillator V9 68N7 2nd Audio Amplifier

V4 6BA6 IF Amp., FM-AM V10 6V6GT Audio Power Output

V5 SAUG IF Amp., FM & 2nd Vll 6V60T Audio Power Output t

Detector, AM V12 SYSGT Rectifier

?John F. Rider

Page 2:


fuse is blown.

gang condenser.
support bracket of the switch.


Test Eguipment


A fuse is provided for protection of the receiver against excessive
power line voltages, and against failure of any component in the re-
ceiver which would cause heavy current drain and fire hazard.
fuse is accessible at the rear panel of the tuner chassis.
Always replace the fuse with one of the same rating in the event the
If the fuse continues to blow after replacement
trouble is indicated and the equipment should be removed from the
cabinet for examination.

Voltohmyst for DC measurements.

AM signal generator for 455 KC, 1500 KC, 600 KC, 10.7 MG,

89 MC and 107 MC.

AC voltmeter such as the Ballantine voltmeter.

An aligning tool is included with each receiver and is taped

on the 1st FM-IF

may be had by ordering under part number 94V4707.

Alignment Procedure

The alignment is preferably performed in the following order:
Figure l for location of adjustments on chassis.

AM-IF Alignment

A signal generator capable of modulation and accurately set to 455 KC
should be attached through a .Ol MFD capacitor to the lug on the ser-
vice selector switch which connects to the middle AM section of the
A good ground point for the generator is the rear

transformer can.

In order to reduce instability due to ground currents it is advisable
to have a metal sheet covering the test bench and to place all gener-
ators and the receivers to be tested on this metal plate.

The AC voltmeter is placed across the secondary of the audio output
transformer, which is loaded with a B ohm 10 watt resistor connected
in place of the speaker voice coil.
not available the speaker may be used if the noise can be tolerated.
The volume, bass and treble controls must be full on, the service
selector switch in the AM position, and the tuning dial in any con-

In the event this resistor is


Additional aligning tools


(C)John F. Rider

venient position that does not interfere with the AM-IF output signal."

Page 3:


Apply sufficient input signal at 455 KC, 50% AM modulated at 400
cycles to give an indication Of about 2 volts rms AC on the AC volt-
meter across the secondary of the output transformer. With the use of
an aligning tool the primary and secondary of the two AM-IF trans-
formers are peaked for a maximum indication on the output voltmeter.
As the receiver approaches correct alignment, reduce the input signal
level so that the output never exceeds 5-4 volts AC. It is good prac-
tice to recheck the peaking of the transformers a second time, es-
pecially if the set was badly out of alignment. The normal AM-IF
sensitivity is such that when 100 uV are applied with the signal gen-
erator, the output voltmeter will read 2 volts minimum.

AH-RF Alignment

Apply the signal generator to the lug on the service selector switch
that supports the loop lead (loop not connected). The Ac voltmeter
remains attached as for the IF alignment. The operating controls also
remain as for the IF adjustment of the receiver. Set the signal gen-
erator and receiver dials on 600 KC at 30% modulation with 400 cycles
and adjust the AM oscillator core (top adjustment on the l 1/8"

square can toward rear of chassis) for a maximum indication on the
output voltmeter. Keep the generator input low enough to prevent the
voltmeter from reading above 3-4 volts AC at all times.

The AM converter transformer (top of l 1/8" square can toward front
of chassis) is now adjusted for a maximum output indication on the

The generator and receiver dials are now set at 1500 KC and the osc-
illator and converter gang condenser trimmers (front holes in the gang
cover) are adjusted for a maximum output on AC output voltmeter.

The above procedures are repeated until the 1500 KC and 600 KC points
on the generator and the receiver dials coincide without further ad-
justment of the cores or trimmer condensers.

A sensitivity of lO uV or less at 400 cycles 30% modulation for a 5
volt AC output and a 10 db Or greater signal to noise ratio is normal
for this input point. l

The loop is then attached to the receiver and the generator is applied
to the loop tap which is available on the antenna strip at rear of

the receiver. The generator and the receiver dials are set to 1500 F
and the antenna trimmer capacitor on the 1st AM section of the gang
condenser is adjusted for maximum output on the AC output voltmeter.

A sensitivity of 1 uV at 400 cycles 30% modulation for a 2 volt AC
output with a 10 db signal to noise ratio or better at 1500 KC and
600 KC is normal for the receiver at this input point.

Place the service selector switch in the FM position. Apply a signal
generator unmodulated, and set accurately to 10.7 megacycles, to the
grid tap on the FM converter coil. The rear mounting bracket of the
service selector switch provides a convenient ground point for the

(C)John F. Rider

Page 4:



A DC voltohmyst voltmeter is connected from ground to the negative
side of the 5 MFD electrolytic capacitor (0-57) which is across the
two 8200 ohm load resistors (R-SO, R-Sl) of the ratio detector.

Enough signal at 10.7 MC is then applied to the receiver to give an
indication on the voltohmyst above the residual voltage already
present. Always keep the input level of the signal generator low
enough to produce not more than negative 5 volts DC on the voltohmyst.

The following FM-IF transformer cores are then adjusted in the follow-
ing order for a maximum indication on the DC voltmeter:

l. Primary of ratio detector (bottom of large can).
2. Primary and secondary of 5rd FH-IF transformer.
3. Primary and secondary of 2nd FM-IF transformer.
4. Primary and secondary of lst FM-IF transformer.

If the receiver was badly mis-aligned it is advisable to repeat the
above procedure for better alignment.

The voltohmyst is then connected to the audio out t of the ratio
detector which is the junction of the 47 000 ohm watt resistor
(R-27) and the 1500 MMFD capacitor (0-36; and ground.

By tuning the secondary of the ratio detector (top of large can) it
is possible to produce both positive and negative swings of the DC
voltmeter from a zero position. The proper tuned position is the
zero position of the voltmeter between the positive and negative

In order to check the relative sensitivity of the Fl-IF system move
the voltohmyst back to the first position from the negative side of
the 5 MFD capacitor to ground. A normal sensitivity is indicated

when it is necessary to apply between 500 and 700 uV for a negative
5 volts DC on the voltohmyst.

FM-RF Alignment

Connect a signal generator unmodulated and accurately set on 89 IC
to the FM antenna terminals of the receiver through a resistor of
200 ohm to 270 ohm in the hot lead of the generator to match the
300 ohm input of the FM antenna coil. The DC voltmeter is connected
as it was for the FM-IF alignment, between the negative side of the
5 MFD capacitor (0-57) and ground.

Set the tuning dial of the radio to 89 HC and adjust the Fl oscilla-
tor core for a maximum DC output on the voltohmyst. Adjust the
input level of the signal generator so as to produce a negative 5 to
5 volts DC on the voltmeter. The correct oscillator core position
is when the core is just entering the coil from the bottom of the
'coi1. The 2nd harmonic of the oscillator is used to produce the IF
frequency. By compression or expansion of the converter and antenna
FM coils it is possible to bring their circuits into alignment with
the oscillator at 89 MC.

(C)John F. Rider

Page 5:



As the set becomes more accurately aligned it may be necessary to

reduce the input of the signal generator to maintain an output below
a negative 5 volts DC.

New reset the signal generator and the receiver dials to 107 MC and
adjust the oscillator tubular trimmer and the compression trimmers on
the FM converter and antenna sections of the gang condenser for a
maximum indication on the output DC voltmeter.

Again reset the generator and receiver dials back to 89 MC and repeat
the operations performed formerly at this frequency setting. This
realigning at the high and low ends of the FM band is necessary until
it is noticed that at both 89 MC and 107 MC the receiver has been
aligned to the generator frequency without adjustment of either the

core of the oscillator or the oscillator trimmer to bring them into

The converter and antenna coils have been properly aligned when either
compression or expansion of the turns will give no increase in the
output DC voltage at 89 MC and the converter and oscillator trimmer

condenser adjustment will also give no increase in DC output voltage

Pin Pin Pin Pin Pin un Pin Pin
v5 owe c 0 6.5 0 11'0 110 1-2 -

e readin s made with vexcohmyse. Line 'mirage adjusted to
gga'ltngC. Allsvoltages measured between indicated pin and chassis
frame. Unless noted all voltages are DC and positive to frame.

521:32" takgn with the service selector switch in the PM position.
Volume control in the counterclockwise position.
Tone controls clockwise.

(C)John F. Rider

Page 6:



REAR oF cHAssls
Figure 1 Model 510 Receiver Assembly

(C)John F. Rider

Page 7:


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(C)John F. Rider

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