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valent to
a
continuous frequency
vari-
ation,
and
thus the
frequency
varies
up and
down
at
vibrato
rate.
PERCUSSION AMPLIFIER
(See
Figures
5-1
through
5-4).
-
The 2nd
or
3rd
harmonic
signal,
or both,
when
these tabs are de-
pressed,
will
be impressed
upon
the input
of the
2N306
transistor.
The
output of
this
transistor
is
resistance
coupled
to the
one
half
of
VI
1
which
acts as a
control
tube
and
is
normally
conducting,
so
when
a
t
key
is
depressed the
percussive
note
first
sounds
loudly.
It
passes
through
the control
tube
and
a
band
pass
filter
and
is
impressed
on
the
grid
terminal
of VI.
Immediately
the
note
begins to fade
away,
giving
the
characteristic
percussion
effect.
This fading
is
accomplished
as
follows:
When
jf
either
harmonic
stop
is
depressed the key-
i
ing
wire (normally held
at
plus
28
volts
through
anti-spark
resistor
R21
5)
is
con-
nected
to solo
manual
6th
harmonic
draw-
bar.
When
a
key
is
pressed
this
keying
hne
^
is
grounded through
the
key
contact
and
tone generator
filter.
This
virtually
grounds
the
grid
and
plate
of
VI
1
(connected
as a
diode) open-circuiting the tube
and
isolating
[
the control tube
grid
circuit.
The
grid
of
the control tube
drifts
from
its
operating
potential
of about 25
volts to a
cutoff
potential
potential
(about
plus
1
5 volts) at
a rate
determined
by
the
time
required
for
C210
3
to discharge
through
R219
and R409.
The
percussion
signal
is
now
blocked.
No
percussion notes can
sound
until
all
keys of
2-5.
the solo
manual
are released
and
the control
grid
again
rises
to plus
25
volts.
The
time of
this
rise
(that
is,
how
quickly the control
tubes turn
on
again
after
the
key
is
released)
is
the
time
required to charge
C2
1
0
to plus
25
volts
through
R2
18.
When
a
''percussion" tab
is
pressed the solo
manual
second,
third,
or
both harmonic
*
manual
busbars
are
connected
to the green
percussion
signal line
and
a 5
OHM
series
resistor
is
connected between
the
manual
bus
wire
and
drawbars
providing
for a
sus-
tained
signal in
addition
to
the percussion
signal.
The
6th harmonic drawbar
is
dis-
connected from
its
lead
wire
and
this
wire
(which
is
grounded through
the
generator
magnets
when
any key
is
pressed)
is
used
to turn off the control tube.
Therefore the
6th
harmonic
is
not
available
on
the
upper
manual
when
the percussion
is
in use.
When
the
PERCUSSION SOFT
tab
is
down,
it
reduces the
volume by
shunting
resistor
R224
into the dividing
network
composed
of
R222
and R223.
The
PERCUSSION FAST
DECAY
tab
determines
how
fast
the
sound
fades
away
after a
key
is
pressed.
When
the tab
is
up,
resistor
R21
9 discharges capacitor
C21
0, re-
ducing
the D.C. voltage
on
the control
tube
grids
to cut-off
in
about
2-1 /2
seconds.
When
the tab
is
down,
resistor
R409
is
shunted
across
resistor
R21
9,
reducing the
time
to discharge capacitor
C210
and
there-
by
reducing
the D.C. voltage
on
the control
tube
grid
to cut off
in
less
than
one-half
second.
With
either
or
both
2ND
and
3RD
HAR-
MONIC
tabs
down,
the
harmonic drawbar
wires are
connected
to the
-green signal
input
wire
of
the
percussion
amplifier.
Either or
both
signals
are fed
back
to their respective
drawbars
by
resistors
R410
and
R41
1
which
are
shorted
out
when
the percussion
tabs
are
not
in use.
The
percussion
signals as
well
as
the
signals
from
the vibrato
and
phase
shift
amphfier
are
combined
in
the input
circuit
of cathode
follower
VI
and
are sent to the
expression
control,
which
is
also
connected
to the
input
of
the reverberation
and
power
amplifier.
REVERBERATION
AND POWER
AMPLIFIER
(See Figure
5-4).
-
The combined
signals
from both
prior
mentioned
amplifiers
(after
the expression control has acted
upon
them)
are
impressed
on
the
grid
of
V6
and
in
turn
on V7,
the reverberation
drive tube.
After
passing
through
the reverberation unit the
signal
is
again
ampUfied by
V6
and
passed
through
a
resistive
network,
components
of
which
are variable,
permitting the
reverbera-
tion to
be
available in several intensities
and "off.
From
the input
of
V7
(the
reverberation
drive
tube)
a signal
is
shunted
around
the reverberation unit
and
its
control
features
which
provide
a
path
for
the
non-
reverberation
signal.
The
input
of
V8
re-
ceives
this signal as
well
as a
reverberative
signal.
This
common
input
line
also
contains
the
VOLUME
SOFT
tab
circuitry.
The
output of the second
half
of
V8
is
a
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