www.SteamPoweredRadio.Com
filJIICK
TO
IIWTl'VI
IIIU
Ml
..
Cl
••
It
Cl • m
II
MTl'Vl
SIii!
cu
Simplified Schematic,
In
put
Stage
and
Pha
se
I
nve
rter
...
to d-c ground (
th
e grid is
at
a-c grou
nd
because
of
th
e low impedance
of
capacitor C2).
Th
e
tw
o outputs
of
the
phase inverter are
coupled to the grids
of
output tubes
V3
and
V4
through capacitors C4
and
C3.
The
output
stage
is
a
standard
push-pull power amplifier.
flOllftar(ISTIIL
>-1-----
"
C>
rn
"
H
1--+-----<1--
·
llNHN'fl
nut
"...__
__
__._
_.....__..
..
..
II
Sim
,plifi.ed Schematic, Power
Am
,plifier
After power amplification,
the
signal is ap-
plied to the co
mp
ensation network through
output
tran
sfo
rm
er
Tl.
The
compensation
net
-
work, which consists
of
capacitors
CS,
C9
, and
ClO
and resistors
RIS
, R16,
and
Rl7
, provides
the necessary inverted ima
ge
of
th
e speaker
and
enclosure
charac
teristics which resul
ts
in
virtually
fl
at
acoustical response.
The
com-
pensation network acts as a passive filter and
also provides feedback to tube Vl.
The
equali-
zation network, consisting
of
capacitor
Cl
1.
resistors R18, R20, and
R21
and
potentiometer
Rl9
, provides the tonal compensation desired
by the listener.
Wh
en
an
ext
ernal
speaker
is
plugged into
EXTERNAL SPEAKER
ja
ck J2,
the
compensa-
tion network
(bu
t not the feedback
or
the
4
f!Oltb.
r
I
,_n
I
JII
1,1
I
_
..
'
I
L--
••
<tolNMSAI~
•
ll(lWffO
C!t
'"
,,
U
ll
'
.l"
l
S,OJll
Simp
l
ified
Schematic, Conipensati.Oll Networh
equalization network) is bypassed providing
flat signal response
at
th
e speaker jack.
SERVICE
NOTE
S
Certain cir
cu
it c
haract
eris
ti
cs
of
the
Mod
el
622 should be understood before attempting
m
eas
urements
or
servicing. (See
Schematk
Diagram.)
1.
While
response
of
th
e
622
(
in
c
ludin
g
speaker) is acoustically '{lat. the r
es
ponse of
the
amp
lifier. measured
at
the internal
speaker terminals, is
not
flat.
The
amplifier
response is flat
only
when measured across
a 12-ohm load plugged into the EXTERNAL
SPEAKER jack.
2.
The
phase inverter,
V2,
is
of
the differ
ent
ial
type. Note, however, t
hat
the
gr
id
of
the
second section, V2b, is
at
ground potential
wit
h respect to a-c only (due to the l
ow
im
-
pedance of
C2)
and
is approximately 100
volts positive with respe
ct
to d
-c
ground.
For
service access to tubes. remove the
four
r
etai
ning screws from
the
front panel
of
the
amplifier. For access to
und
er-c
ha
ssis parts. r
e-
move
th
e screws
at
the forward edge~
of
th
e
amplifier chassis. and pull
th
e front panel for•
ward and down.
No
attempt should
be
made to service the
speaker.
or
to remove
it
from
the
case.
1f
servicing
is
required during the warranty
per
i
od
,
return
the
entire Model 622 to
yo
ur
nearest
AMPEX
dealer
or
authorized service
center.
