Dynaco Mark VI Service Manual

Page 4

DESCRIPTION

The Mark V] is a vacuum tube high power basic power
amplifier designed for the professional sound installer.
Vacuum tubes are most often favored in their ability to with-
stand enormous physical and electrical abuseswconditions
frequently encountered in discotheques, public address and
musical strument applications. Its rugged construction
and utilization of superior components, including the
patented Dynaco Super Fidelity transformers, permit con-
tinuous duty at full power, while maintaining safe operating
margins. Protective isolation of the load from the driving
circuits, and uniform power output into a variety of load
impedances are inherent in all designs which use an impe-
dance matching transformer.

Thc Mark VI employs a basic circuit arrangement which
all Dynaco vacuum tube amplifiers have used since the
inception of the Mark II amplifier in 1955. Refinements of
the operating parameters have been incorporated for circuit
balance, stability, and for drive capability. The components
used have been selected to protect against failure, and all
parts are operated conservatively to assure superior per-
formance and proper operation for many years.

The pentode section of the 7199 tube is a high gain voltage
amplifier, which is direct-coupled to a mthodyne-split
load-phase inverter. The operation of this type of phase
inverter is independent of tube aging, a unique advantage

of its design. The input gain and inverter stages are refined
to provide an accurately balanced signal to the output tubes.

The 8417 output tubes are a matched set of four, to assure
proper operation of the Mark VI. The output tubes are op»
erated in a fured bias arrangement, which may be accurately
checked and adjusted with the lighted meter and recessed
potentiometer on the front panel.

The output tubes drive a Dynaco Super Fidelity output
transformer expressly designed for this circuit. Taps on the
plate windings connect to the screen grids, and contribute to
the linearity of the overall design. The impedance match
and bias conditions employed contribute to very low distor-
tion over a wide range, even without feedback. The overall
feedback loop adds 20 decibels of additional distortion re
duction.

In addition to front panel adjustment of bias, recessed con-
trols for input level and a 4-position range switch (three
positions for observing output power levels on the meter,
plus one position for observing bias) are supplied. A speaker
fuse holder and lighted power switch complete the front
panel layout.

The simplicity of this circuitia minimum of phase shift-
ing stages and very careful attention to output transformer
(lesigniassures maximum stability.

INSTALLATION

The Mark VI is designed for mounting in a standard 19"
rack (mounting hardware for the rack is not supplied); its
supplied large feet also permit placement on any flat sur-
face. The amplifier should be installed where the front panel
is accessible. If the Mark V1 is to be mounted near a phono-
graph, chcck to make sure that the phono cartridge does not
pick up hum from the power transformer.

VENTILATION isan important consideration. This amplifier
generates almost the same heat under quiescent (no signal)
conditions as it does at full power-the equivalent of a 250
watt light bulb within the confines of the perforated cage.
Thus, ADEQUATE AIR CIRCULATION IS ESSEN-
TIAL. If the Mark VI is rack mounted, 1 foot (30 centi-
meters) of unimpeded air space Mus'r be provided above
the unit. Otherwise fan cooling is recommended. Also, the
amplifier is intended to be installed horizontally, with its

feet providing clearance for air flow under the unit. Do not
allow the ventilation slots in the bottom to be restricted
(don't place the amplifier on a mg, for example), or there
will be excessive heat buildup within the enclosed section of
the chassis. Vertical mounting is not recommended, even
with fan cooling.

If the amplifier is to be permanently installed, the ban»
dles may be removed before instalhtion, if desired. The
bolts which affix the handles to the front panel should he
reinstalled once the handles have been removed, since these
bolts also attach the front panel to the chassis. However, the
handles not only facilitate carrying the Mark VI, but: they
also protect the front panel components from breakage.
Therefore, unless it is to be permanently mounted, their re-
moval is not. suggested.

CONNECTIONS

INPUT

A signal input is connected by a single conductor shielded
cable to a choice of two RCA type phono jacks or an XLR con-
nector. One of the phono jacks and the XL]: input provide flat
low frequency response; the other phono jack provides a low
frequency rolloff @ 6 do per octave (~53 d5 @ 70 Hz). The
input impedance is 50,000 ohms, unbalanced line. The input
sensitivity is 1.6 volts rms for 120 watts output with the input
level control turned fully clockwise. The Mark VI may
therefore be easily driven by one channel of many brands of
control preamplifiers, such as the Dynacc PAT-5, YAT4,
PAS/«3x, or PAS-2/3. The PAS tube type preaniplifiers require
internal modification: To change the PAS-3X, simply locate
and remove the pair of 62,000 ohm resistors (blue-red-
orange) on the 905 printed circuit board; to change the
PAS-2 or PAS-3, remove the 62,000 ohm resistors, as indicated

above, and additionally remove the pair of 510,000 ohm re-
sistors ( green-brown-yellow) on the back panel of the pre-
amplifier.

Some other tube type preamplifier brands may require
modification for optimum performance into a 50,000 ohms
load.

OUTPUT

Select speaker leads of sufficient size to preserve the
damping factor of your amplifier. Standard 18 gauge lamp
cord (zip cord") is suitable for distances up to 30 feet.
Larger wire sizes are advised [or longer distances #16 for
50 feet; #14 for 80 feet. #18 and #16 lamp cord is available
from hardware and electrical supply stores, and is the
easiest to use and conceal.

4 Bob01605@aol.com

Page 10

l5( )Select the last 1,000 ohm, 1/2 watt resistor (brown-
black-red ) , bend its leads 90° to its body, and cut its
leads to 1/2 ( 1.3 cm) each. Connect one lead to V5
pin #5 ( S) . Connect the other laid to V5 pin #6.

The leads in the next 2 steps are deliberately long. They
will be arched toward the bottom plate for clearance.

16( )Prepare a 35/4 (95 cm) black wire. Connect one end
to V2 pin #6 (S-Z). Connect the other end to V3
pin #6.

17( )Prepare a 3% (9.5 cm) black wire. Connect one end
to V5 pin #6 (8-2). Connect the other end to V4
pin #6.

18( )Select the blue-white and the green-white leads from
the output transformer. Twist these leads neatly to-
gether, and connect the green-white lead to T-l lug
#1 at the base (S). Connect the blue»white lead to
T-l lug #2 at the base (S). Make certain that these
leads are not interchanged,

19( )Select one of the 22 ohm, 2 watt resistors (red'red-
black). Bend one load 90 to its body, and cut that
lead to %" ( 1 cm). Do not bend the other lead, but
cut it to 5/3 (1.8 cm). Connect the bent-lead end to
V2 pin #4 (S) . Connect the other lead to T»l lug #1
at the tip.

20( )Select another 22 ohm, 2 watt resistor (red-red-
black). Bend one lead 90" to its body, and cut it to
A3 (1 cm). Connect the bent-lead end to V3 pin #4
(S). Connect the other lead to T-l lug #1 at the
tip (52).

21( )Select another 22 ohm, 2 watt resistor (red-red-
black). Bend one lead 90 to its body, but do not cut
it. Cut the other lead to l (2.5 cm). Connect the
bent-lead end to V2 pin #3 (S). Connect the other
end to T-l lug #2 at the tip. Trim off any excess lead
at V2 pin #3.

22( )Strip a 1%" (4 cm) piece of insulation from the roll
of yellow wire, and out the insulation in two equal
lengths. Set aside one length until it is called for.

23( )Select another 22 ohm, 2 watt resistor (red-red-
black). Bend one lead 90° to its body, do not cut it,
but slip a length of insulation on it. Cut the other
lead to 3A (2 cm). Connect the bentelead end to V3
pin #3 (S). Connect the other end to I-1 lug #2 at
the tip (S-2 ). Trim off any excess lead at V3 pin #3.

24( )Select the red, the green, and the blue leads from the
output transformer. Twist these leads together, and
connect the red lead to ()3 lug #4. Although a total
of four wires will eventually be soldered to this lug,
we suggest connecting this lead close to the base of
the lug (next to the terminal screw), and soldering
it. Connect the green lead to T-2 lug #3 at the base
(S). Connect the blue lead to T-2 lug #4 at the
base (S).

25( )Select another 22 ohm, 2 watt resistor (red-red-
black). Bend one lead 90° to its body, and cut it to
% (1 cm) . Cut the other lead to %" (1.8 cm). Con-
nect the bent-lead end to V4 pin #4 (S ). Connect the
other lead to T»? lug #3 at the tip.

26( )Select another 22 ohm, 2 watt resistor (redirede
black), Bend one lead 90° to its body, and cut it to
A" (1 cm). Connect the bent-lead end to V5 pin #4
(S). Connect the other lead to T-2 lug (#3 at the tip.

10

27(

28(

29(

3M

31(

32(

33(

34(

35(

35(

37(

38(

39(

)Select another 22 ohm, 2 watt resistor (red-red-
black) . Bend one lead 90 to its body, but do not cut;
it. Cut the other lead to 1" (2.5 cm). Connect the
bent-lead end to V4 pin #3 (S). Connect the other
end to T-2 lug #4 at the tip. Trim 05 any excess lead
at V4 pin #3.

)Select the last 22 ohm, 2 watt resistor (red-red-
black). Bend one lead 90" to its body, do not cut it,
but slip the remaining length of insulation on it. Cut
the other lead to 5/4 (2 cm). Connect the bent-lead
end to V5 pin #3 (S). Connect the other end to T2
lug #4 at the tip (S-2). Trim off any excess lead at
V4 pin #3.

)Select the black lead from the output transformer,
and connect it to C1 ground lug B".

)Select the brown lead from the output transformer,
and comiect it to output barrier strip lug #2 (S).

)Prepare a 2%" (7 cm) black wire. Connect one end
to output strip lug #3. Connect the other end to out-
put jack lug #1 (S).

)Select the orange lead from the output transformer,
and connect it to output strip lug #3 (S-2).

)Select the 620 ohm, 2 watt resistor (blue-red-brown) ,
bend its leads almost 90" to its body, and cut its
leads to 3/4 (2 cm) each. Connect one lead to output
strip lug #4 Connect the other lead to output strip
lug #1.

) Prepare a 141/2 (37 cm) black wire. Connect one
end to output terminal lug #4. Position this wire
adjacent to the orange and brown leads from the out-
put transformer, and connect the other end to T-4 lug
#4atthe base (S).

)Select the yellow lead from the output transformer,
and connect it to output strip lug #4 (S-3) .

)Prepare a 31/2 (9 cm) black wire, but remove 3/.
(2 cm) of insulation from one end, and the usual 1/4
(6 cm) from the other. Feed the long-stripped end
through output jack lug #2 to lug #3, and solder both
lugs. Connect the other end to output strip lug #1.

JPrepare a 121/4" (31 cm) yellow wire. Connect one
end to output strip lug #1 (S-3). Position this wire
next to the brown, orange, and yellow wires from the
output transformer on the right of the chassis, and
feed it out the hole in the front of the chassis. The
other end of this wire remains without connection at
present.

)Prepare a 9 (23 cm) yellow wire. Connect one end
to C1 ground lug C" (S). Quite a bit of heat is re-
quired to solder the outside ground lugs on this ca-
pacitor. The other end of this wire is not: connected
at this time.

)Select the four plastic ties. Group together the blue,
the brown, the orange, and the yellow wires con-
nected to the output strip and bind them together
with two of the ties for a neat appearance, as shown
in the Pictorial Diagram. Slip the male end of a tie
under the group of wires. push the male end through
the female end, pull it tight, and cut off any excess.
In a similar manner tie together the other wires in
the vicinity of the output transformer, as shown in
the Pictorial Diagram.

Page 13

100,000 ohms, 1 w., 10%

4,700 ohms, 1/2 w., 5%

1,000,000 ohms, 1 w., 5%

240,000 ohms, 1 w., 5%

620 ohms, 1 w., 5%

100 ohms, 1 w., 5%

100,000 ohms, 1/2 w., 5%

22,000 ohms, 1 w., 10% (matched
within 1% to R9)

22,000 ohms, 1 w., 10% (matched
within 1% to R8)

47,000 ohms, 1 w., 10% (matched
within 1% to R11 and R12)

R 11 47,000 ohms, 1 w., 10% (matched

within 1% to RIOand R12)
R 12 47,000 ohms, 1 w., 10,, (matched
within 1% to R10 and R11)

R101 240,000 ohms, 1 w., 5%

R102 10,000 ohms, 1 w., 10%

R103 18,000 ohms, 1 w., 10%

R104 18,000 ohms, 1 w., 10%

R105 220,000 ohms, 1/2 w., 10%

R106 220,000 ohms, 1/2 w., 10%

R107 220,000 ohms, 1/2 w., 10%

R108 220,000 ohms, l/2 w., 10%

R109 22 ohms, 2 w., 10%

R110 22 ohms, 2 w., 10%

R111 22 ohms, 2 w., 10%

R112 22 ohms, 2 w., 10%

R113 1,000 ohms, 1/2 w., 5%

R114 1,000 ohms, 1/2 w., 5%

R115 7.8 (or 7.87) ohms, 3-5 w., 1%

R116 1,000 ohms, 1/2 w., 5%

R117 1,000 ohms, 1/2 w., 5%

R118 22 ohms, 2 w., 10%

R119 22 ohms, 2 w., 10%

R120 22 ohms, 2 w., 10%

R121 22 ohms, 2 w., 10%

R122 620 ohms, 2 w., 10%

R123 5,600 ohms, /2 w., 5%

alternate (Japan) 7,500 ohms, 11/; w., 5%

R124 5,600 ohms, 1/2 w., 5%

alternate (Japan) 7,500 ohms, 1/2 w., 5%

R125 12,000 ohms, 1/2 w., 5%

alternate (Japan) 15,000 ohms, 1/2 w., 5%

R126 2,940 ohms, 1/2 w., 1%

SUNFUFUNNNN
u: mummprn-I

1321
H
o

D101 Diode, 1 a., 200 prv

D102 Diode, 3 a., 1,000 prv
D103 Diode, 3 a., 1,000 prv
D104 Diode, 3 a., 1,000 prv
D105 Diode, 3 a., 1,000 prv
D106 Diode, 1N541 Germanium

COMPONENT VALUES

115104
113472
1.16105
116241
116621
116101
113104

1 15223

115223

115473

115473

115473
1.16241
115103
l 15183
115183
112224
11.2224
11.2224
11.2224
11.0220
110220
118220
115220
113102
1.1.3102
120078
113102
113102
119220
11.8220
113220
118220
113621
113562

113752
113552

713752
113123

113153
130294

5440 12
544323
544323
544323
544323
543541

1 .068 mfd,500 v.,5%,my1ar

2 22 P1, 500 v., 5%, mica

3 68 Pi, 500 v., 5%, mica

4 .5 (or .47) mid, 500 v., 10%, mylar
5 .5 (or .47) mfd, 500 v., 10%, mylar
6 390 Pf, 500 v., 5%, mica

7 150 Pf, 1000v., 5%, mica

C101 _05 (or .047) mfd, 200 v., 10% mylar
C102a/b 50/50 mid, 450 v., electrolytic
C103 50 mfd, 75 v., electrolytic

C104 50 mfd, 75 v., electrolytic

C105 100 mid, 300 v., electrolytic

C106 100 mfd, 300 v., electrolytic

C107 50 mfd, 300 v., electrolytic

0108 50 mid, 300 v., electrolytic

C109 .02 mid, 500 v., 20%, disc

C110 .02 mid, 500 v., 20%, disc

OOOOOOO

V 1 Tube, 7199

V102 Tube, 8417 (matched with V103,
V104 and V105)

V103 Tube, 8417 (matched with V102,
V104 and V105)

V104 Tube, 8417 (matched with V102,
V103 and V105)

V105 Tube, 8417 (matched with V102,
V103 and V104)

TD101 Tube, time delay, 6N030T

P101 Potentiometer, 100,000 ohms, carbon,
audio taper

P102 Potentiometer, 10,000 ohms, carbon,
linear taper

CH101 Choke, .85 H., 400 ma, 13.5 ohms

F101 Fuse, power, 5 a., AGC/3AG
alternate 2.5 a., AGC/3AG (220-240 0. wiring)
F102 Fuse, speaker, 5 a., AGC/3AG

M101 Meter, 31/2
ML101 Meter Lamp, #337
ML102 Meter Lamp, #337

5101 Switch, power
3102 Switch, meter

T101 Transformer, power
alternate (Japan)
T102 Transformer, output
alternate (Japan)

267 $83
257220
257660
267504
267504
257391
258 151
265473
297 107
284506
284505
255 107
235 107
235506
255506
227203
227203

517004

517008

517008

517008

517003

5 14003

1441.04

145103

423355

342025
342022
342025

508031
525001
526001

3311.03
333169

464023
46401 7
4543 55
454354

13

Page 18

INITIAL ADJUSTMENT-BIASET

Plug the line card into a conventional 120 volts AC line
(alternately 100 volts, 220 volts or 240 volts), and turn the
power switch on. It is safe to operate the Mark VI without
connection to the input or the output. The red lamp in the
power switch and the lights in the meter should glow. While
the tubes are becoming warm, on the front panel turn the
meter range switch to the Adjust for 0" position, and turn
the Biaset potentiometer to approximately its center of rota-
tion. A bladed screwdriver adjusts these recessed controls.
Although the meter will begin showing a bias reading
quickly, it will take at least 30 seconds before the output
tubes draw their correct current. After almost a minute,
adjust the Biaset potentiometer to read 0 on the meter.
Allow the amplifier to operate this way for three or four more
minutes, and readjust the Biaset control to read 0 once
again, if necessary. There may be some drifting of the read-
ing as the output tubes are initially used, but this will sta-
bilize within an hour, after which no further adjustment is
required at this time It should be understood, however, that
this voltage is in direct proportion to line variations and
therefore it is normal for there to be small changes. These
will have no effect on performance.

After initially setting the bias, turn the meter range switch
to the next (-3 da) position.

Although the adjustment of Biaset is semi-permanent, it
is good practice to check this voltage three or four times
during the useful life oI the output tubes (LOGO-1,500 hours) .
If the amplifier is used continuously, Biaset should be
checked at least weekly. If the amplifier is in a mobile instal-
lation, we recommend checking the Biaset every time the
amplifier is set up in a new location. Of course, it must be
checked and reset at times of output tube replacement or
other types of repair or maintenance work.

The Biaset adjustment must be made when no signal is
going through the amplifier, for it is normal for this voltage
measurement to vary considerably with signal going through
the amplifier.

If it is not possible to set bias-the control range of the
potentiometer is insufficient to obtain the correct 0 read-
ing do not operate the amplifier until the cause of the dif-
ficulty has been established. Operation with incorrect Biaset
can lead to damage to the output tubes and/or to other
components.

OUTPUT METER READING

The action of the meter supplied is fast" enough to re-
spond to substantial musical peaks, but no meter can
accurately indicate the magnitude of transient waveforms
which occur in music. However, with an accurate 4, 8 or 16
ohm load, the meter is a measure of output power. A square
wave test signal puts out approximately 11% more voltage
than the equivalent sine wave meter indication.

To protect the meter from pegging toverdrive), it is
recommended that the -3 dB position of the recessed meter
range switch be used where the anticipated power levels are
not known, and when starting any test. Switching to sue-
cessively higher ranges (-9 dB or -15 dB) until the loudest

18

passages indicate near 0" will yield the most information.
The accompanying chart lists 4 ohm, 8 ohm and 16 ohm
load power outputs in watts for each meter range.

m RANGE

SCALE -3 (is -9 da -15 (18
+ 3 120 30 7.6
0 60 15 3.8
- 3 30 7.5 1.9
-10 6 1.5 0.38