Be sure to maintain similar wiring "sense" for each
speaker in a mono, stereo, or quadraphonic system, so that
they will be connected
in phase.
Normally the "-", common, or
ground terminal of each speaker is attached to the "c"
terminal on the output barrier strip, or to the "sleeve" con-
nection on the output jack. The other speaker terminal is
attached to the correct impedance terminal (4, 8, 16) on the
barrier strip (the "tip" connection on the output jack is nor-
mally wired to the 8 ohm tap of the output transformer,
although this connection may be changed to either the 4
ohm or the 16 ohm tap, if desired). Proper phase sense is
easily maintained with lamp cord because one conductor is
coded with a molded ridge on the outer insulation.
Two speakers are connected in phase when maximum low
frequency output is heard when they are driven from a mono-
phonic source. Lowered output is observed when the con-
nection to one of the speakers is reversed (out of phase, or
reversed polarity). When using multiple speakers on each
channel, or with 4-channel systems, it is important that all
of the speakers in the same area be wired in phase.
If stranded lamp cord is used, the wire ends should be
"tinned" first with solder to avoid fraying. In any case, make
certain that no wire strands can touch other than the in-
tended terminal.
The "c" terminal of the amplifier is connected to the
chassis, so the Mark VI may be used in multiples, if desired,
with special output connections which require common
grounds. If so, it will be necessary to connect together all
the "c" terminals of the Mark VI amplifiers being used in
the same system.
An in-phase signal at the input of the Mark VI amplifier
provides an in-phase signal at the output. This is char-
acteristic of all Dynaco tube and solid state amplifiers.
AC POWER
The power cord should be plugged into a wall outlet pro-
viding 120 volts, 50/60 Hz (alternately 100 volts, 220 volts
or 240 volts depending on the wiring of the primary of the
power transformer). Do not attempt to switch the amplifier
remotely by plugging it into a switched outlet on a control
preamplifier unless the outlet is designated as a 5 amp, or
higher capacity. The Dynaco
PAT
-5, which can handle 15
amps, may be used.
LOUDSPEAKER RATINGS
Nominal speaker power ratings are a matter of concern.
There is currently no U.S. standard. Manufacturers usually
provide a "music power" rating, or indicate amplifier power
limits. These should not be confused with continuous, or
"rms" power acceptance for a sustained period which will be
substantially lower. It is rare for a speaker to be able to
handle as much power near the frequency extremes as in the
midrange. Single woofer high fidelity speaker systems rarely
have "music" ratings as high as 100 watts, or continuous
duty wide band sine wave ratings as high as 40 watts.
In view of the power limitations of most high accuracy
speaker systems, the connection of two or four similar
speakers in the same location to a single channel is often
advisable, if high signal levels are wanted. Lacking more
definitive advice, a rough test is to place your hand in front
of the woofer when playing a loud passage at your antici-
pated listening level. If you can feel
any
heat generated by
the voice coil, you should consider the need for additional
speakers to reproduce that level safely. When high output,
high accuracy reproduction is desired, a series-parallel con-
nection of four 8 ohm speakers (such as the Dynaco
A
-35)
on each channel provides a resultant 8 ohm load with excep-
tional power handling capacity.
Speaker impedance varies with frequency—often by a
factor of 4 or 5 to 1. Even the least variable speakers, like
Dynaco's, have a 2:1 change. While most nominal ratings
are close to the actual minimum impedance, when combina-
tions approach the 4 ohm minimum recommended amplifier
load, the safest procedure is to measure the resistance across
the terminals with an ohmmeter. Speaker impedance usu-
ally varies upwards from this value. Use this figure to de-
termine how multiple speakers should be connected:
IN PARALLEL:
IN SERIES:
IN SERIES-PARALLEL:
2 x 8 ohms
=
4
ohms 2x4 ohms = 8 ohms 4x16 ohms =16 ohms
2x16 ohms =8 ohms 2x8 ohms =16 ohms 4 x 8 ohms= 8 ohms
4x 16 ohms =4 ohms 4x4 ohms= 16 ohms 4 x 4 ohms= 4 ohms
These simple examples assume identical models. It is not
wise to connect dissimilar speakers in series or in series-
parallel because of adverse audio effects.
LOUDSPEAKER FUSING
The output of the Mark VI is provided with a speaker
fuse, which is mounted on the front panel. The 5 ampere,
3
AG
fuse supplied will not fail when the amplifier is operated
at full power (120 watts into 8 ohms), and therefore it pro-
vides
NO PROTECTION
for your speaker. The size of the fuse
should be determined by the type of speaker you are using.
The protective fuse rating determination for a speaker is
largely empirical, because the power passed by a fuse varies
with load impedance, test signals have little correlation with
music signals, and fuses vary in their tolerance of music
overloads. Logic would suggest the smallest fuse which does
not blow frequently at what are high, but nonetheless safe
levels for your speaker. There are few speakers capable of
safely handling more power than will blow a 2 ampere fuse.
The speaker manufacturer who specifies a fuse rating
solves your problem. Lacking this, remember that a fuse will
not blow until a
sustained
signal
well above
its rating is im-
posed for a time. A slo-blo fuse will allow appreciably more
overdrive than the same value standard fast-blow type, and
is thus not generally recommended for speaker protection.
The chart below shows the highest
sustained
power level
which will
not
blow the fuses shown. Remember that speaker
impedance typically rises well above its nominal value.
Experience suggests that on this basis power levels of 10
watts are safe starting points for most high fidelity speakers
using a single woofer.
3
AG FUSE TYPE
4 OHMS
8 OHMS
16 OHMS
1
/
2
ampere
l watt
2 watts
4 watts
3
/
4
ampere
2.2 watts
4.5 watts
9 watts
1 ampere*
4 watts
8 watts
16 watts
1
1
/
2
ampere**
9 watts
18 watts
36 watts
*Dynaco A-10, A-25 and A-35 speakers
**Dynaco A-25XL, A-40XL, and A-50 speakers
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