Receive Mode Selection; Block Diagram - SEA 222 Operator's Manual

6.1.1
Two carrier insertion potentiometers are provided on the main board.
R29 and R30 control the reinsertion level in the A3A and A3H mode,
respectively.
RECEIVE MODE SELECTION
Since the SEA 222 as normally supplied always operates as a normal
upper sideband only SSB receiver, little mention need be made of
alternate modes of operation.
AM reception is by the
11
exhalted carrier" o.r "zero beat" method.
That is, the incoming signal is simply tuned in until the carrier wave
is zero beat with the internal BFO. This technique has proven com-
pletely adequate for those applications where voice fidelity is de-
sired. For reception of music, the internal I.F. and AF filters
sharply limit the level of fidelity which may be achieved.
7. THE POWER SUPPLY CIRCUIT
7.1 GENERAL
7 .1.1
The basic supply voltage for the SEA 222 is a negative ground 13.6
Volt DC source.
Line voltage regulation of ± 15% or better is
required, with a current capacity of at least 25 - 30 Amperes.
From this raw source are derived the necessary regulated operating
voltages for the SEA 222 circuitry.
BLOCK DIAGRAM
Figure 7.1.1 shows a simplified schematic diagram of the power supply
circuitry.
Once the basic 13.6 Volt power is provided, it is connected to the set
through the heavy duty power plug, Pl, on the rear panel. Three
internally mounted fuses are provided to protect the set in the event
of malfunction. Each fuse has a reverse voltage protection diode which
will blow the fuse ·in the event of reversed line polarity.
The ON/OFF switch is part of the volume control potentiometer. From
this switched 13.6 Volt buss, protected by 5 Amp fuse F3, all other
required voltages are derjved, EXCEPT the high current 13.6 Volt buss
to the final amplifier transistors.
Several regulators, located throughout the set, distribute the re-
quired voltages. All the +10 Volt busses are derived from the 10 Volt
regulator on the main board.
I