HH Scott 222 D Service Bulletin
- SPECIFICATIONS
SERVICE BULLETIN
For
MODEL 222D STEREO AMPLIFIER
Maximum power output each channel at 1000 cycles: Music waveforms.
Maximum total harmonic distortion at rated OUÉPUE, ..oéacoorcccooooo
Steady state, * . e
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Frequency response for 20 watts steady state at less than 1,0%
total distortion......esecooocoarrooocaocacooaaoooooooooooorooeooo
Power bandwidth at rated distortion (IHFM method)......oococoo
Signal for rated output--NAB (NARTB) tape at l kKC....eocooococcooo
Signal for rated cutput--RIAA equalization at 1 KC.....eoseocooooo
Signal for rated output--RIAA equalization at 1 kKC....oeooscoooooa
“Signal for rated output--Ceramic,Tuner,Extra, and Playback.....e..
Hum and NOÎSE. 0 2000000 0000000 100 0 0 0 0 0 0 0 a 0 0 a secs eu a a a Ga 0 à
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%
<>" Scratch Filter......eocoscocaocoocococadacecoreoooraocooocaoooo
Treble boost and Treble cut (at 10 kc.)
Bass boost and cut (at 50 cycles)
(These characteristics are measured at a line voltage of 117 volts rms
60 cycles per second.
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24 vatts
20 watts
0.8%
20 to 20,000 cycles =
20 to 20,000 cycles *
„3.0 MV,
„3.0 mv; (MAG LOW)
.9.0 mv. (MAG HIGH)
..0.50 volts
.
.80 db. below rated powe'
.Above 5 kc.
‚15 db. + 2 db,
15 db, + 2 db.
and line frequency of
No significant, changes of characteristics should be experienced for
normal variations of line voltages or a line frequency of 50 cycles per second.)
Input impedance--low level inputs......oeoe.roscoscorccococoreococo
Input impedance--high level iNputS,e..oscocroscccaccdoooooaocaoeaooaeo
Minimum recommended load resistance on tape Ooutputs....e.oococoocoo
Maximum recommended cable capacitance on tape Outputs.......e.ee..
Range of line voltage and frequency... 000500000000 0000000000
Power consumption--117 volts at 60 срз (А.С. оп1у)................
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Approx. 50 k. ohms
500 k. ohms
200 k. ohms
200 mm£ds.
105-125 volts,
50-60 cycles
170 watts
* All H. H. Scott amplifiers and preamplifiers incorporate a sharp cutoff filter (12 db, or
sharper per octave) which becomes fully operative below 20 cycles,
- vent overload of the output stage and the loudspeaker due to subsonic rumble frequencies and
record eccentricity,
the audible range,
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(1)
This is designed to pre-
This means that the full power c£ the amplifier can be concentrated into
D-222D-2
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GENERAL SERVICE NOTES
Check the tubes, particularly those in the power output stage and the rectifier every
Pa
year. If the tubes are outside the manufacturer's rating or show gas, they should be ¿+
replaced. Gassy tubes may damage other components of the circuit.
When the amplifier is being checked yearly, clean the tubes of dust so that they may
“radiate their heat more effectively.
If, at any time, the hum or noise increases noticeably, check the power tubes. This
symptom is often an indication of gassy tubes.
If the amplifier blows fuses frequently, check the line voltage. If it rises above
125 volts, drop the line voltage by means of an auto-transformer or place a voltage
regulator transformer between the amplifier and the line. If the line voltage is
correct, check the amplifier itself, Do not use fuse sizes other than the fuse size
specified.
Pilot Light Replacement
a. Remove tube V102,
b. Remove the pilot light assembly by inserting a sharp instrument (a screw driver
or knife) between the Control Shield and the Assembly Clip.
c. Remove the old bulb and install the new #47 bulb,
d. Reinstall the light assembly by snapping it into the hole. Reinstall the tube
and tube shield. >
D. С. Balance Adjustment
To make this adjustment, a short audio cable which has an audio (phono) plug on one end
and bare wires on the other is needed. Insert the plug into the Right Channel Tuner
input, and connect the two bare wires to the Left Channel speaker terminals (High and 0).
Connect a loudspeaker to the Right Channel speaker terminals (High and 0). Connect the
Green wire that comes through the plastic grommet to the Right Channel speaker impedance
terminal which matches the impedance of the speaker being used. Remove V3 (a 6U8 tube).
Set the controls as follows:
Input Selector.,....sceoocomnccaaaeoo, UNE
Power Switch. ....eoooscecooccocaoos e ОЁЕ
Stereo Selector....ececseacocoresoe.Stereo
Bass and Treble Controls..........0
Stereo Balance......:i..+.+.+.+.0».....0
Loudness ContrOl........000000000.0
CompenSatOT.......0.........00.000.00.Loud
. Tape..oscosresococacerdoroocao ooo. DUE
SCYraAfCNo 0000000000 000000 000000000. Out
Speaker Soc..0000000 0000000005000 0,00
EqualizatioNn.................0....,Either Position
Insert the line cord into an A.C. outlet and turn the unit on. Wait a few minutes for Mu
the amplifier to completely warm up. Slowly turn the Loudness Control clockwise until ©
you can just hear a low hum in the loudspeaker. (If you turn the volume up too high,
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or
the amplifier will oscillate and produce a motorboating noise). Take a small screw-
driver and adjust the L Channel balance adjustment control (on top of chassis) for
minimum hum, (Hum is a 120 cycle low frequency noise--do not confuse it with any
high frequency noises present),
Turn off the amplifier and replace the tube V3. Connect the audio cable to the Right
Channel speaker terminals (High and 0) and insert the plug into the Left Channel tuner
input, Connect the loudspeaker to the Left Channel speaker terminals (High and 0).
Connect the Red wire that comes through the second plastic grommet to the Left Channel
speaker impedance terminal that matches the speaker impedance. Remove V103 (the other
6U8 tube). Keep the front panel controls the same. Turn on the unit, and adjust the
R Channel balance adjustment control for minimum hum. Turn off the amplifier and
replace V103, |
Bias Adjustment
a. Set the L and R Bias Adjustment Controls to their extreme counter-clockwise
positions.
b. Connect an audio cable from Bias Test Point L to Channel L Tuner input.
с, Set the Front Panel controls as follows:
Power Switch.................Off
Input Selector................Tuner
Stereo Selector...............Stereo
Bass (L € R)...oeoccsocaroceaco .EXtreme counter-clockwise
Treble (L & R)................<Flat (0)
BalanCE ..,........0.....0....s.0.. Flat (0)
LoOudneSS...00000000000000000000 |
Equalization..................Either
TapeC....0000000000 000000000000 ut
SCFratCh.....000000000000 000000. Out
SpeakKerS..cosocsooccocoocooooso, ON
Compensator...escseccoscooooooe VOL.
d. Turn the unit on and turn the Loudness control full clockwise.
e, Locate the Bias Adjustment Switch on top of the chassis and slide the button
back and forth. This will produce a CLICKING sound in the speaker.
Е, Continue to slide the button back and forth causing the click to continue. At
the same time, using a small screwdriver, turn the L channel Bias Adjustment control
clockwise slowly. The click will become very faint and then begin to increase,
Readjust the control to the point where the click is the faintest,
a
g. Remove the audio cable from Test Point L and insert the plug into Test Point R.
h. Repeat the procedure outlined in steps e. and £. but adjust the R channel Bias
Adjustment Control.
i. Because these two controls interact somewhat, you should repeat steps f, g, and h
alternately until the faintest amount of clicking is heard.
(3) —
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Control Positioning:
"Tape-Monitor Switch.........0ut
NOTE:
|
+
INSTRUMENT ALIGNMENT
Equipment Needed:
Audio Oscillator
AC VIVM
Oscilioscope
Volt-Ohm Meter
Load Box
Attenuator
400 cps Null Filter
AC
VTVM
Input Selector..............Extra ATT. NULL 16 OHM
StereO...orococcocodavocecooeooe. IE EYreO wey >
Tone Controls...............Flat ("O0") FILTER LOAD
Loudness Control............Maximum.
Stereo Balance....ce.eoccooooo 0" | |
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Pickup SWitCh...............F1 | TO FROM
Scratch Filter..... ......s...Out | UNIT UNIT
Compensator...e.e.e.ooccoo +... Loud
Speaker Switch......…........0n
Due to variations in tubes, voltages at the plates (pin 6) and screen grids (pin 3)
of V3-A and V103-A may have a differential of as much as 30%. Normal is approxi-
,mately 50v. A 10% variation may be found on all other tubes.
Balance Adjustment
(It is suggested that the VOM not be used in this adjustment as there may be too much
voltage drop. A 100 to 500 full scale non-switchable milliameter should be used
instead.)
Connect a 16 ohm load to the 16 ohm speaker terminals. Remove both phase splitter
tubes and adjust the DC balance pots for minimum meter reading. Do this for both
channels, With the phase splitter tubes still removed, set the bias to 44ma (both
channels) with the bias pots, measuring from the Cathode Current Test Points on the
chassis.
Sensitivity Check
Connect the audio oscillator, through the attenuator, into the Left Channel Extra
Input Jack. Set the audio oscillator to .4v output at 400 cps. The Output reading
on the VIVM should be 18v (20 watts), undistorted. The input voltage of ,4v may be
adjusted to + 2 db to obtain the 18v output. Connect the oscillator to the Tuner
input jack and move the Input Selector switch to the Tuner position. You should
obtain the same output as in the above.
Distortion Check
«
Using the 400 cps null filter, the distortion must be no greater than 0.67 as read
on the VTVM. ‘
Tone Control Check
Bass (50 cps) Treble (10 ke) >
Boost 15 db 11 db
Cut 15 db 15 db + 2 db
Be certain that electrical zero agrees very closely with mechanical zero.
(4) < <x
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