Scott 340B Service Bulletin Late

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H. SCOTT IN

I" POWDER MILL HD.. MAYNAHD. MASS-y 131754

SERVICE BULLETIN FOR

MODEL 3405 TUNERzAMPLIFIER

(Serial No. 235581 and Above)

SPECIFIFICATIONS
TUNER FM-MPX)
Usable Sensitivity (IHF) 2.2 microvolts
Spurious Response Rejection (Cross Modulation Rejection) 80 db
Signal to Noise Ratio 60 db below 100% modulation
Total Harmonic Distortion 0.8%
Frequency Deviation (Drift) 0.02%
Frequency Response (Stereo) '50 to l5,000 cps 1 l db
Capture Ratio 6.0 db
Selectivity 35 db
AM Suppression 55 db
Tuning Range 87 to 109 mc
Accuracy of calibration 0.5%

Separation

Better than 30 db

This is limit of FCC Stereo Broadcast specifications. All H. H. Scott tuners have far wider frequency
response.

TAPE OUTPUT

Rated Voltage Output to rlape Recorder 0.5 v
Minimum Recommended Load Resistance 100 K
Recommended Cable Capacitance - Less Than 1000 mmf
Maximum Recommended cable Length 40 feet

PIKE-AMPLIFIER

Input
Tape Head and Mag. Low - Input Impedance
- Signal for Rated Output
Mag. High - Input Impedance
Signal for Rated Output
High Level Inputs - Input Impedance
Signal for Rated Output
Frequency Response in Flat Position
Treble Controls Measured at l0.000 cps, Boost and Cut
Bass Controls Measured at 30 cps, Boost and Cut
Scratch Filter

AMPLIFIER

Music Power (18?)

Steady State (rms)

Maximum total harmonic distortion at rated output
Frequency Response r _

Power band width at rated distortion (IHF method)
Hum and Noise

Approximately 50 K

3 mv

Approximately 50 K

9 mv

500 K

0.4 v

20-20 kc 1 1.0 db

15 db ,+_ 2 db

l5 db _+_ 2 db

-6 db/octave over 5 KC

35 watts each channel

30 watts each channel
0.8%

20 to 20,000 cycles 1; 1 db

**20 to 20,000 cycles

80 db below rated power

(These characteristics are measured at a line voltage of ll7 volts ms and line frequency of 60 cycles
per second. No significant changes of characteristics should be experienced for normal variations of
line voltages or a line frequency of 50 cycles per second.)

105-120 volts. 50-60 cycles
200-280 watts

Range of line voltage and frequency
Power consumption - 117 volts at 60 cps (AC only)

'All H. H. Scott amplifiers and pre-amplifiers incorporate a low frequency roll-off filter which be-
comes fully operative below 20 cycles. This is designed to prevent overload of the output stage and the
loudspeaker due to subsonic rumble frequencies and record eccentricity. This means that the full power
of the amplifier can be concentrated into the audible range.

GENERAL SERVICE NOTES

Service. other than replacement of" either pilot lights or vacuum tubes, is usually not required. If
the tuner is not operating properly, all external connections should be checked. The amplifier section
can be checked by playing a record through the pre-amp in PHONO position. Then, the vacuum tubes should
be checked by replacing them with new ones. one by one. The tubes should be tight in their sockets and
provided with shields where applicable. Tube defects frequently do not show up in a tube tester. Only
operation in the tuner/amplifier will insure that the tube is functioning properly. When replacing tubes.
if possible, use exact replacement tubes, available from H. H. SCOTT or any authorized Warranty Service
Station. Other tubes will work, but only exact replacements can give the full performance from the
tuner/amplifier .

D- 3403- 23

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Pilot Light Replacement
1. Remove the sheet metal screws on top and on each end of the controls shield which covers the
top, front section of the unit, and carefully lift the shield up and backwards. There are
wires connected to the shield so do not pull it too far.
2. Remove the dial indicator lights by squeezing in on the spring clips and pulling backwards.
The replacements should be bayonet type #47 bulbs. Be sure to remove the "beam shields"
from the old bulbs and reinstall them on the new bulbs.

3. If the meter bulb, located on the control shield, needs replacement, it will be necessary to
contact the factory for the replacement. When ordering, specify number VPL-47-Blue.

4. Reinstall the control shield in the same manner as it was removed and replace all five screw:
Dial Cord Replacement

1. If the dial cord should break, a replacement may be ordered from our Parts Department by spec
ifying number ADC-8. If a new dial cord spring is required, number ASP-l should be specified

2":-

I
POINTER AT as

ALTERNATE METHOD
BRACKET

ALIGNMENT INSTRUCTIONS FOR FM SECTION

When checking the FM tuner section, take the output from the "TAPE OUT" jack on the rear of the
chassis. Leave the "LEVEL" control full counter-clockwise.

The recommended test equipment for aligning H. H. SCOTT PM tuners is as follows:

Oscilloscope

VTVM

Distortion Analyzer or 400 cycle null filter
Measurements ZlOAB PM Signal General or equivalent

Under no circumstances should a sweep generator be used to align H. H. SCOTT equipment as this will
give false indications of alignment due to loading of the individual circuits. When peaking the front
end and IF sections, the input should be as low as practical to avoid mis-aiignment and to make sure
that the unit is completelypeaked.

FRONT END ALIGNMENT

Oscillator Adjustments: The oscillator trimmer on the top of the front end and the oscillator coil en-
closed in the bottom shielded section of the front end are used to adjust dial tracking. Tune to a sta-
tion on the low end of the dial (88-95 mc) whose broadcast frequency is known. If the station is higher
than it should be, turn the oscillator trimmer screw slightly counter-clockwise until the station is
shifted to the proper point on the dial. Now check a station of known broadcast frequency on the high
end of the dial to determine that proper tracking has been maintained across the entire band.

If stations on the low end of the dial are tracked correctly but the stations on the high end of
the dial are received at a higher frequency, tune to a station on the low end of the dial whose frequen-
cy is known. Remove the small tab from the shielded section on the bottom of the front end and slightly
squeeze the oscillator coil closer together. Keeping the dial in the same place, turn the oscillator
trimmer counter-clockwise until the station is back at its original point. Tune to the high end of the
scale and note that the stations have come down slightly in frequency. These adjustments should be con-
tinued until the high end and low end of the dial track perfectly.

If the low end of the dial tracks correctly, but the high end of therdial is low, the reverse pro-
cedure is used. That is, the oscillator coil is spread slightly apart and the oscillator trimmer is
turned clockwise.