Scott 222C Service Bulletin

Page 1

SPECIFICATIONS

Maximum power output each channel at 1000 cycles:

Maximum total harmonic distortion at rated output.....

l

i339?-

MODEL 222C STEREO AMPLIFIER

11 Powdermill Road. Maynard, Mass.

SERVICE BULLETIN
For

Music waveforms...

Steady state......

...............

Frequency response for 20 watts steady state at less than 1.5%

total distortion......
Maximum usable power output at 20 cycles:

...-..............................

Music waveforms...

Steady state......

Power bandwidth at rated distortion (IHFM method)....................

Intermodulation distortion............... ...... ............ .........
Signal for rated output - NAB (NARTB) tape at l kc..................
Signal for rated output -- RIAA equalization at l kc ............ .....
Signal for rated output -- RIAA equalization at l kc.................
Signal for rated output -- Tuner, Extra, and Playback ........... .....

Hum and noise -- high level inputs.........................

Hum and noise -- low level inputs..........................

Scratch filter......
Treble boost and Treble cut (at 10 kc.).....................
Bass boost and cut (at 50 cycles)............................

.................................~.......... .....

24 watts
20 watts
0.8%

20 to 20,000 cycles *
28 watts
24 watts
below 19 cycles to *
above 20,000 cycles
(limits of test equip)

below 0.5%

3.0 mv.

3.0 mv. (MAG LOW)
9.0 mv. (MAG HIGH)
0.50 volts

80 db. below rated
power

10 microvolts equiva-
lent

Above 5 kc.
15 db. 1 2 db.
15 db. i 2 db.

(These characteristics are measured at a line voltage of 117 volts rms 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).

Input impedance -- low level inputs (MAG LOW).......... ..... .........
Input impedance -- low level inputs (MAG HIGH)................ ..... ..

Input impedance -- high level inputs........................

Minimum recommended load resistance on tape outputs........
Maximum recommended cable capacitance on tape outputs........ ..... ...

Range of line voltage and frequency.... ..... . ..... ...................

Power consumption -- 117 volts at 60 cps (A.C. only)

47 k. ohms
150 k. ohms
500 k. ohms
200 k. ohms
200 mmfds.

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.

This is designed to pre-

ient overload of the output stage and the loudspeaker due to subsonic rumble frequencies and

record eccentricity.
the audible range.

95 222 012

This means that the full power of the amplifier can be concentrated into

(over)

Page 2

GENERAL SERVICE NOTES

1. Check the tubes, particularly those in the power output stage and the rectifier every year
If the tubes are outside the manufacturer's ratings or show gas, they should be replaced.
Gassy tubes may damage other components of the circuit.

2. When the amplifier is being checked yearly, clean the tubes of dust so that they may
radiate their heat more effectively.

3. If at any time the hum or noise increases noticeably, check the power tubes. This symptom
is often an indication of gassy tubes.

4. 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.

5. D.C. Balance Adjustment:

Equipment Needed - Oscilloscope and/or AC VTVM, 16 ohm resistive load of adequate
wattage (some wirewound resistors have considerable residual inductance and these
should be avoided).

The balance pot for each output stage is located between the output tubes for that
stage. These controls should be adjusted when the output tubes age appreciably or
are replaced. To set these controls use the following procedure:

(a) Connect the 16 ohm resistor across the output terminal of the channel under test.

(b) Connect the oscilloscope and/or VTVM across the resistor, and turn the horizontal
selector of the scope to "LINE".

(c) Remove the phase inverter tube 6U8/6GHB of the output'stage under test.

(d) Adjust the proper D.C. Balance Control for a minimum 120 cycle response on the
scope or minimum reading on the AC VTVM.

(e) Repeat the entire procedure for the other amplifier output stage.

6. Tests can be performed to insure that the unit meets or exceeds the specifications out-
lined previously. Only use parts and tubes specified by H. H. Scott, Inc. The use of
non-standard parts or tubes will preclude obtaining the performance stated in the
specifications.

If you have any further questions, write to: Technical Services Dept.
H. H. Scott, Inc.
I2AX7 12AX7 12AX7 2AX7 111 Powder Mill Road

@ . ® Maynard, Massachusetts
0 3:54

sua/
eEHa

7.15?
no.
5:°R4 am $.79

7159
L V! - v5 CHANNEL A vzcn REDHFIER
v

Inlrvms CHANNELS N- 222 TL zJ

so c
Gut