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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