BGW 250 User manual

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OWNERS MANUAL MODEL 250
STEREO POWER AMPLIFIER
S ER I AL ~JUMBER
rJ 4/1'='
BGW SYSTEMS
P.O. BOX 3742
BEVERLY HILLS, CALIF. 90212
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H1PORTArJT --PLEASE READ THIS PAGE BEFORE OPERATING
YOUR BGW POWER AMPLIFIER
YOUR NEW RGW POWER AMPLIFIER IS DESIGNED TO PROVIDE YEARS OF
TROUBLE FREE PERFORt"1ANCE. OnSERV I NG THESE Fnl PRECAUT IONS
WILL INSURE PROPER OPERATION.
ilEVER CONNECT THE OUTPUT OF OtlE CHAWJEL \'IHI THAT
OF M!OTHER.
l' lEVER CONNECT A DIRECT SHORT FROM THE OUTPUT OF ANY
CHANNEL TO GROUND.
ONLY CONNECT THE POWER COgD I8 THf PROPE~ MAINS
(NORMALLY THIS WILL BE lO~-12 VOkTS AC ~O-6UHZ).
SEE SECTI ON ~t_ FOR CONVERS ION TO L4u VOLT OPERAT I ON.
ONLY MAKE CONNECTIONS TO THE POWER AMPLIFIER ~IITH THE
POWER OFF.
Do NOT REMOVE FACTORY SEAL. AMPLIFIERS ~IILL NOT
BE COVERED UNDER WARRANTY IF SEAL IS BROKEN. THERE ARE
.tlQ. ADJUSTMENTS ~/ITHIN.
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TABLE OF
1. DESCRIPTION
2. SPECIFICATIONS
3. WARRANTY
4. FACTORY SERVICE
5. INSTALLATION
A. UNPACKING
B. MOUNTING
C. OUTPUT CONNECTIONS
D. INPUT CONNECTIONS
E. nC MAINS & CONVERSION
6. OPERATION
7. SCHEMATIC DIAGRAM
8. PARTS LST
9. WARRANTY REGISTRATION FORM
10. SERVICE AUTHORIZATION FORM
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CONTENTS
TO 240 VOLTS

I .
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I-DESCRIPTION:
The BGW 250 is the most advanced dual solid state power
amplifier available. The basic design criteria used are
those which are applied to present day computers and related
equipment.
Unique design features incorporated in the 250 make it
virtually "FAIL SAFE" and free from accidental damage caused
by human error in audio service.
A fast acting SCR (silicon controlled rectifier) crow bar
is employed as a safe guard for your speakers. The sophisti-
cated sensing circuitry for the crow bar constantly samples
the individual outputs of each channel. The outputs of each
channel are integrated and passed through an absolute value
detector. The output of the detector is connected to a compar-
ator which is activated by the presence of a large DC component.
If such a voltage is present the comparator in turn triggers a
fast discharge pulse circuit which fires the SCR crow bar. The
crow bar is essentially a direct short placed across the two
power supplies- If activated this causes abnormally high
current to flow in the primary circuit and within a fraction
of a second the ultra fast acting circuit breaker disconnects
the power. The crow bar circuit quickly discharges all energy
stored in the power supply internally, not into the speaker;
thus protecting the load.
The packaging inside your 250 is unlike ordinary power
amplifiers. Each channel assembly is on its own separate
module, which simply plugs in or out for quick and easy
service. Each of these units is constructed on a tremendous
aluminum extrusion. The total radiating surface area of
each heat sink is 330 square inches. The heat sinks have
mating circuit boards which carry the passive components.
Each unit's wiring is identical with the next as the circuits
are photo etched. The heat sinks plug in with an 8 pin
connector.

The output stage of your 250 uses the most powerful type of
transistors available. The large geometry single diffused
devices have the largest safe operating area of any type of
transistor available. All the semiconductors in the output
stage are in intimate contact with the heat sink. The
dynamic bias circuit is also mounted on this isotherm providing
rock steady bias stability with temperature.
The voltage gain circuits are also mounted on the same
circuit card. A true operational amplifier
integrated circuit, hermetically sealed in a metal can, acts
as the front end. The op amp (as they are called) is a
special unit featuring high speed (15MHz) and high slew rate
(50 volts/microsecond) yet still having very low noise due
to its darlington input stage and careful design. The op amp
stage is followed by a discrete complementary pair acting
as an active current source/sink and providing additional
voltage gain. The current source is the ideal way to drive
the output stage which is basically a voltage follower.
This sophisticated circuit design makes for an extremely
accurate amplifier. The open loop gain is higher than found
in the competitors' products. The accuracy of an amplifier
is a function of the difference between the open loop gain
and the closed loop gain. In this case the closed loop gain
is 26 db (a voltage gain of only 20) while the open loop
gain is about 1,000,000. The accuracy of the 250 is so great
that conventional audio test equipment is unable to provide
meaningful measurements. Harmonic distortion Measurements
are simply the residual level of the distortion analyzer.
This extremely accurate signal processing enables the 250
to drive speakers at very high levels while adding
absolutely no coloration of its own. EVen at milliwatt
levels the output waveform exhibits no sign of crossover
distortion. The dynamic range capability of a typical 250
is almost 115 db.
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2- SPECIFICATIONS
TIle following specifications are guarranteed mInImum perfor-
mance levels, not typical or best cnse numbers measured under
ideal conditions. All test procedures used are according to
the most conservative techniques in use today.
POWEK OUTPUT: 8S-watts average continuous power per channel
at 8-ohms.
FRf,QIJENCY R[SPONSE:
+0-0.25 dB 201lz to 20KHz
+0-3 dB 211z to 65 Kllz
HARMONIC DISTORTION:
Less than 0.1% at 85 watts per cnannel or less into 8 ohms.
1M DISTORTION: (00 & 7khz 4:1):
Less than .l~ at 85 watts per channel or less into 8 ohms.
tfUM & NOISE (20-20 kHz):
105 dB below HS watts into 8 oj~s
INPUT SENSITIVITY:
I volt +2% for 20 volts out (SO watts, 8 ohms)
voltage-gain of 26 db (20xL 1.5 volts required for full outpuL
INPUT H!PEDANCE:
47,000 ohms
DAMPING FACTOR:
Greater than 500 at low frequencies (8 ohms )
OUTPUT LOAD H1PEDANCE:
Designed for any load impedance greater than 2 ohms.
Haximum
output po'veT occllrs rtt 2 ()l'r~.
RISE TIMBrIO-90t):
5 micro5cconds- inuicat.ing a bandwidth of (IS KlIz.

POWER BAND:
10 Hz to 20 kHz.
POWER REQU I REr-IENT :
105-120 volts 50-60Hz at 5 amps maximum or
210-240 volts at 2.5 amps maximum.
TURN ON:
Anti surge turn on, no switching transients or thump wil l
appear at output.
OUTPUT PROTECTION:
Each channel is p~otected against shorts, open circuit
opcration, mismatched loads, etc.
LOAD PROTECTION:
Exclusive SCR crow bar protccts speakers against malfunction.
OVERALL PROTECTION:
Power line is protected with fast acting computer type
, circuit breaker. No fuses of any kind are used. Two
thermal switches (one per channel) protect against over
temperature operation. Controlled power bandwidth and
slew rate protect tweeters and amplifier against excessive
high frequency operation. Input overload protection is
afforded op amps by series limiting resistance.
POt\,ER SUPPLY:
A large power transformer with twin primary windings is
used. Computer grade electrolytic capacitors storing
over 22 joules of energy, and a 25 amp bridge rectifier
are employed. Two Zener regulated supplies power each
operational amplifier front end.
POWER REQUIREHENTS:
Unit requires either 10S-129V AC or 210-240V SO-60Hz power.
A 5 amp circuit breaker is supplied for units Hired for
120V operation or a 2.5 amp breaker for 240V operation.
HEAT SINKING:
Each channel has its own removable heat sink. Each
extrusion has 330 square inches of surface nrea.

·.
CHASSIS:
A
heavy steel chassis forms a protective cage for unmatched
mechanical strength. A 3/16" aluminum rack mount panel is
supplied. All modules are bolted to the chassis. The power
supply is mounted close to the front panel to allow rack
mounting without the use of guide rails or supports.
CONNECTORS:
Output- standard 3/4" spacing, 5 way binding posts for outputs
(color coded for easy identification).
Input- 1/4" phone jack
AC line- three wire grounded male connector on 5 ft. min.
cable.
MODULES:
3 plug in modules contain 95% of the circuitry. Modules
consist of 2 heat sink channel assemblies and 1 crow bar
trigger circuit board.
CIRCUIT BOARDS:
Flame retardant glass epoxy boards per mil spec.
DIMENSIONS:
Panel 19" Wx 5~ H x 11 3/4" D- brushed satin aluminum.
Notching is standard Western Electric.
WEIGHT:
27 pounds net
35 pounds packaged
shipping container; unique double boxed system using
8 toro pads (trade mark of Hardigg Corp.) between inner
and outer cartons for shock protection in transit.

~~RAANTY
BGW Systems warrants all power amplifiers for a period of
three years from date of manufacture. This warranty covers
both defects in workmanship and materials. If malfunction
occurs, the product will be repaired or replaced ( at our
option) without charge for materials or labor; if returned prepaid
to BGW Systems. The warranty does not cover equipment damaged
due to negligence, misuse, shipping damage or accident, or if
the serial number has been defaced, altered or removed.
Purthermore, units altered, modified or improperly serviced,
in any way, will not be repaired under terms of the warranty.

5- INSTALLATION
a. UNPACKING: Your BGW power amp is shipped in an
advanced double boxed container using 8 energy absorbtion
"Toro Pads" between the inner and outer boxes. The container
should be saved in event the unit is moved or shipped
at some future date. Replacement containers are available
from BGW Systems for $10.00 freight included.
Damage; Inspect the unit for damage in transit immediately
upon receipt. If damage is found, notify the transportation
company immediately. Only the consignee may institute a
claim with the carrier for shipping damage. BGW will
cooperate fully in such event. Be sure to save the container
as evidence of damage for the shippers inspection.
b. MOUNTING: The BGW power amp is supplied with a heavy
standard 19" rack panel. The unit may be bolted into a
rack by the front panel alone.
Regardless of how the unit is mounted, provIsIons
for unrestricted air flow must be provided. Good ventilation
practice will provide for air flow above and below the unit.
Inadequate ventilation may cause the protective thermal switches
to shut the unit off.
Normal installation- all connections should be made before
power is applied!
c. OUTPUT CONNECTIONS: Adequate size wire must be used
between the amplifier and the speakers to preserve damping
factor.
WIRE SIZE (damping factor =50)
Wire
length up to Impedance 4 8 16 ohms
10'
#16 #18 #20
25'
#10 #14
1#16
SO'
#8 # 12 #14
Observe polarity markings when connecting speakers.
Speaker fusing is recommended to prevent overpowering
and damaging speakers. If fuses are not included in the
speaker system they must be connected in series with the
lead to the red binding post on the rear of the amplifier.
Consult speaker instructions for recommended fuse size and type.

4- FACTORY SERVICE:
Should service be required please fill out the Service
Authorization form and mail it to BGW Systems.
All units must be shipped prepaid in the factory supplied
shipping container, to prevent damage in transit. Units
will be returned freight collect.

d. CONNECTING INPUT LINES: Input connections should be
as short and direct as possible. Shielded cables must be
used and both should originate from the same source
(i.e. if both channels do not come from the same pre-amps,
ground loop problems may arise.)
The source must be capable of delivering 1.5 volts for full
output from the amplifier.
For maximum signal to noise ratio driving source impedance
should be less than 5000 ohms. Radio frequency interference
(RFI), when it occurs, can be reduceu or eliminated by
employing one of the filters shown below. They should be
built in shielded enclosures such as 3Smm. aluminum film
cans.
1.8K
600 OHM----'''v\/'v I
T
AMP
SOURCE .003 uF
6db/octave rolloff
above 20l\.bz
5mH(J W Miller 6304)
----~~-~~---
12dB/octave rolloff
600 OHM --L- AMP
above 20l\.!iz
SOURCE
.018uF T
e. A-C MAINS CONNECTIONS: The Model 250 is furnished
with a 3 wire cord and a ground plug. Defeating the grounding
provision may create hazardous conditions.
Amplifiers sold in the United States and Canada are factory
wired for 105-120 volts, 50-60 Hz,S amps maximum. Many
export amplifiers are factory wired (see rear panel of amplifier)
for 210-240 volts, 50-60 Hz, 2.5 amps maximum. Conversion
from 120 to 240 volts or 240 to 120 can he done in the field
by following the instructions below. The circuit hreakerrnust
be replaced. Circuit breakers are available from BGW Systems
for $10.00 each postpaid. Use the following description
., when
ordering:
For 120V- Moue1 250, 5 amp Circuit breaker.
For 240V- Model 250, 2.5 amp Circuit breaker.

Ihe connections shown below arc for 120 volt operation. For
240 volt operation remove the red transformer lead from lup
2 and remove the orange transforner lead from lug 3. Twist
the red and orange leads together, solder and tape.
Note- The Hodel 250 shoulc
1
not be c(,J".necte~ tc any ot:t] et
rated at less than 600 watts.

6- OPERATION
TURN ON: The Model 250 is free from thumps or transients
during turn on.
Often, turn-on transients originate in the pre-amp or tuner.
This is especially true of tube-type units. If this
situation arises, turn the amplifier on after the other
units have had sufficient time to stabilize.
PROTECTION: Three protection circuits are employed in
the Model 250.
1. The fast acting magnetic circuit breaker shuts the
unit down whenever the unit draws excessive current.
2. The exclusive DGW SCR crow bar circuit instantaneously
discharges the power supply capacitors and triggers
the circuit breaker if any conditions exist which
could potentially damage the speakers.
3. Thermal switches mounted on each heat sink protect
the amplifier from thermal failure. The amplifier
will shut off if the heat sink temperature rises ahove
70 degrees C (1580 F) and will turn on again when
the temperature drops. Activation of the thermal
switches usually means that insufficient air
circulation is being allowed.

Shown wired for 120V
R42
10K
C25
0.1
-so
CHANNEL 1
J2@LL-_-'
J3~~ ______________ _
o
+50
NOTE : I.,illllnc. in ohnu. topocitan,. in microfarad. un'e"
CHANNel 2 <both module. identical)
J5 (S)
J6 o
Cll 1000pf
mark.d.
BGW
MODEL
250
Msa 1-74
PRINTED 1:"01 u.s A

8- PARTS LIST
CAPACITORS
Cl
10uF, 25V electrolytic
.65
C2
50uF, l2V electrolytic
.65
C3
47pF, NPO ceramic
.20
*C4,C5
0.047uF, 25V ceramic
.40
*C6,C7 20pF
ceramic
.20
*C8
47pF, NPO ceramic
.20
*C9,ClO
10uF, 50v electrolytic
.65
*Cll,C12
1000pF dipped mica
.40
*C13,C14
O.luF, 100V mylar
.40
*C15
0.68uF, 100V mylar
.85
*C16
O.luF, 100V mylar
.40
C17,C18
0.01, 400V paper
.40
C19,C20
9000uF, 50Velectrolytic
9.50
C2l
lOuF, 50V electrolytic
.65
C22
O.OluF, 100V mylar
.40
C23 l40pF dipped mica
.30
*C24,C25 O.luF, lOOV mylar
.40
*C26 240pF
dipped mica
.35
DIODES
*Dl,D2 lN4745A l6V zener diode 2.87
*D3,D4 lN4003 or lN4004 .69
*D5 lN4752 33V zener
2.87
*D6-D9,DlO IN4003 or IN4004
.69
INTEr,RATED CIRCUITS
*ICI LM3l8H (National Semiconductor) 6.95
CONNECTORS
*Jl 8-pin socket (octal type)
.80
J2,J 5 Red 5-way binding post 1. 20
J3,J6 Black 5-way binding post 1. 20
J4,J7 Open circuit insulated phone jack 1. 00
* These parts in ~ach HS250, double for total parts in each 250.

JNDUCTORS
*L1
O.Suli output inductor
MISCELLANEOUS
~!l
3-wire line cord and plug
H2
25 amp, 200P.I.V. bridge rectifier
PLUGS
P1,P2
8-pin plug (octal type)
TRANSISTORS, ETC.
*Q1
40410 (RCA)
*02 40409 (RCA)
*03 2N2219A
*Q4
2N3S83
*05 2NS954
*Q6-Q11 40636
(RCA)
*Q12
2N5401
Q13
2N4442
Q14
2N4871
or MUlO (Motorola)
Q1S MPS 3394 (Motorola)
RESISTORS
*R1
1 megohm, 5%, ~ watt carbon film
*R2
47.000 ohms, st, ~ watt carbon film
*R3
2,500 ohms, 1%, ~ watt carbon film
*R4
47,000 ohms, 1%, ~ watt carbon film
*RS-R7
1,000 ohms, 5%, ~ watt carbon film
*R8,R9
1,500 ohms, st, ~ watt carbon film
*R10
1,000 ohms, St, ~ watt carbon film
*R11
47,000 ohms, 5%, ~ watt carbon film
*R12
4,700 ohms, 5%, ~watt carbon film
*R13 100 ohms,
Sl ', ~ watt carbon film
*R14 680 ohms,
5%, ~ watt
*R1S,R16
15,000 ohms, 5%, ~ watt
*R17 680 ohms,
5%, ~ watt
* These parts in each IIS250, double for total parts
1. 25
2.25
6.95
1. 00
1. 80
1. 80
.78
2.25
2.85
3.00
1. 26
3.00
1.14
.45
.20
.20
.60
.60
.20
.20
.20
.20
.20
.20
.20
.20
.20
in each 250.

*R18,R19
68 ohms, 5%, ~ watt
.20
*R20
1,500 ohms, 5%, ~ watt
.20
*R2l
500 ohm potentiometer
1. 00
*R22
1,000 ohms, 5%, ~ watt (may vary)
.20
*R23-R25
10 ohms, 5%, 1 watt
.40
*R26-R3l
0.18 ohms, 2 watts, wirewound
.40
*R32
100,000 ohms, 5%, ~ watt
.20
*R33
330,000 ohms, 5%, ~ watt
.20
*R34
100,000 ohms, 5%, ~ watt
.20
*R35
2.7 ohms, 10%, 1 watt
.40
*R36
30 ohms, 5 watts, wirewound
.95
R37 2
ohms, 50 watts, wirewound
1. 00
R38
33,000, 1 watt
.40
R39
10,000 ohms, 5%, ~ watt
.20
R40
33 ohms, 5%, ~ watt
.20
R4l,R42
10,000 ohms, 5%, ~ watt
.20
SWITCHES
Sl 5 amp, l20V or 2.5 amp, 240V circuit breaker
10.00
S2,S3
Normally closed thermal switch 2.50
TRANSFORMERS
Tl
Power transformer 52.50
SUB ASSEMBLIES
*HS250C
Complete single channel amplifier heat sink
167.00
*CB250
Crowbar trigger module
12.50
f\1ECHANICAL COHPONENTS HS-250
1 heat sink extrusion 15.90
1 printed circuit board 7.90
1 TO-5 mounting clip .85
8 mica insulators .20
16 nylon shoulder washers .10
16 6-32 x 5/8 RH plated steel Phillips machine screw
16 6-32 x ~ plated steel hex nut
16 #6 internal tooth lock washer
2 4-40 x ~ RH plated steel Phillips machine screw
2 4-40 x 5/16 flat head Phillips
6 #4 internal tooth lock washer
heat sink compound

MECHANICAL COMPONENTS CHASSIS
4
4
8
4
6
4
2
8
8
8
7
6
2
8
8
7
6
1
6
5
1
1
1
1
1
1
4
PACKAGING
1
1
10-32 x 1 FH Phillips
10-32 x ~ FII Phillips
10-32 x 3/4 Hex socket cap screws
10-32 x ~ pan head Phillips
8-32 x ~ pan head Phillips
6-32 x 3/4 pan head Phillips
6-32 x ~ pan head Phillips
#6 sheet metal screws
10-32 chrome plated cap nuts
10-32 hex nuts
8-32 hex nuts
6-32 hex nuts
#6 x ~ spacers
#10 split lockwashers
#10 flat washers
#8 split lockwashers
#6 external tooth lockwashers
Heyco SP-4 strain relief
flat blade lugs
round lugs
ground strap (back panel)
ground strap (capacitors)
3-lug terminal strip
steel chassis
aluminum cover
aluminum rack panel
feet
set of cartons
10.00
I-exterior carton
I-interior carton
8-Toro-Pads
owners manual
,.

-----------------------------------------
lO-SERVICE AUTIlORIZATIDtJ FORM
Please complete this form as completely as possible
and return to BGW Systems before returning unit.
NN1E--------------------------------------------
ADDRESS
UNIT
--f"j.,...O .... n ..... ErL--
SERIAL NUMBER
1. Describe symptoms:
2. Which channel(s) exhibits the problem?
3. What other equipment was involved?
Manufacturer Hodel No.
Preamp
Speakers
4. Under what
conditions
does
the problem occur (check
those that apply.)
a.
all the time
b.
after a
while
c.
at high
volume levels
d.
at high temperatures
e. other (explain)
S.
How often did the problem occur?
6. What did you do to isolate the problems to the power amp.
7. Further comments:
*It is more expediant to call your dealer or our factory
explaining the nature of your problem. In many instances
the problem can be solved without returning the unit to the
factory. WARNING: the unit must be returned in an
original factory container, if you do not have one,
we will proviJe a replacement for $10.00.