Scott 299C Service Bulletin

Page 1

SPECIFICATIONS

7SCVOTT

111 Powdermlll Road, Maynard, Mass

SERVICE BULLETIN
For

MODEL 299C STEREO AMPLIFIER

PRICE an

Maximum power output each channel at 1000 cycles: Music waveforms... 40 watts

Maximum usable power output at 20 cycles:

Power bandwidth at rated distortion (IHFM method)

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

Steady state......-35ewatts.,
Maximum total harmonic distortion at rated output............
Frequency response for 35 watts steady state at Iess than 2.0%
total distortion.................

Music waveforms...
Steady state......

0.5%

20 to 20,000 cycles

*0 db.

Intermodulation Distortion.......
Signal for rated output --
Signal for rated output --
Signal for rated
Signal for rated
Hum and noise -- high level inputs...........
Hum and noise - low level inputs.............

........

Scratch filter.............
Treble boost and Treble cut (at 10 kc.)..
Bas boost and cut (at 50 cycles)...........
R le Filter...............

..... ..o..

V(These characteristics are measured at a line volta

of 60 cycles per second.

NAB (NARTB) tape at l kc........
RIAA equalization at 1 kc..............}.....
output -- RIAA equalization at l kc...
output -- Tuner, Extra, and Playback...,...........

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

.........-

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

42 watts
36 watts

below 19 cycles to *

above 25,000 cycles
(limits of test equip)

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

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

................-.........
..........-...........J.

Below 0.5%

3.0 mv.

3.0 mv.(MAG 1&2 LOW)
9.0 mv.(MAG 1&2 HIGH)
0.50 volts

80 db. below rated pwr

10 microvolts equiva-
lent.

Above 5 kc.

15 db. 1 2 db.
15411:, i 2 db.
Belowaloo cycles

ge of 117 volts rms and line frequency
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 l & 2 LOW)............
Input impedance -- low level inputs (MAG l & 2 HIGH)

Input impedance -- high level inputs...

.........-........c.

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

Minimum recommended load resistance on tape outputs.....................

Maximum recommended cable capacitance on tape outputs.............

Range of line voltage and frequency..........
Power consumption :- 17 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.

200 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-

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

record eccentricity.
the audible range.

D-ZQQC-Z (revised)

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

(over)

Page 2

;ENEPAL SERVICE NOTES . '

1.

Check the tubes, particularly those in the power output stage and the rectifier every yeaf
..If the tubes are outside the manufacturers ratings 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
LS 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.

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 tesL

(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 7199 of the output stage under test.

(d) Adjust the proper D.C. Ba ante 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.

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.
111 Powder Mill Road
Maynard, Massachusetts