Advertisement
CIRCUIT DESCRIPTION
O OUTLINE
TL-911
linear amplifier circuit is shown
in the block diagram of Fig. 1.
The
hybrid
type amplifier employs
6 vacuum
tubes,
3 transistors,
27
diodes, and 1 thyristor.
The unitized sections are so arranged that each
unit performs a different function
of the amplifier, thus permitting the
final amplifier
section
to be completely
shielded, and the rectifier and
control units independently mounted on the printed circuit boards, etc.
O FINAL
POWER
AMPLIFIER
SECTION
The five 6LQ6 tubes are enclosed in a shielded box containing a powertul
cooling fan.
The tube operation is Class AB for SSB and Class C for CW in
a grounded-grid configuration.
The required bias switching is accomplished
by means of the LINEAR
ON switch.
The screen grid voltage to obtained
from a regulated power supply, thus assuring freedom from distortion.
In
addition,
a dynamic
balance
circuit which
maintains
uniform
dynamic
characteristics
among
the power
tubes,
a dual
type
ALC
circuit
for
improved linearity, and an SWR meter circuit are included.
O POWER
SUPPLY
SECTION
The
individual supply voltages from a large power transformer having a
current capacity more than actually required are rectified by rectifier unit
X43-1010-00.
The high voltage for the tube plates is obtained
from a
bridge rectifier composed of 8 diodes (10D 10); voltage for the screen grids,
bias circuit and relays are supplied by 10D4 and 10D1.
O OPERATION
OF PROTECTION
CIRCUIT
109
resistors R1, R3, R5, R7, and RY are inserted
into the cathode of
each power tube.
When current flows through the cathodes, the resistors
develop voltages, which are fed to the protection circuit through the diode
matrix.
Operation
of the protection circuit, therefore,
is determined
by
the cathode current.
The protection circuit is designed to operate when
a cathode current of
240 mA
continues for 20 seconds
or more, or 400 mA
or more
flows
instantaneously through a power tube.
If a 240 mA current flows through the cathode of one of the power tubes,
a voltage (2.4 V) develops across the cathode and is applied to the input of
the protection
circuit to increase the potential
across capacitor C16
(220uF).
When this voltage increases to 1.2 V, it causes transistor Q3 to
produce approximately 0.7 V across the emitter, which turns the thyristor
on.
The thyristor turn-on
results in actuation of relay RL1 connected to the
collector of the transistor.
Relay RL1
in turn removes the supply from
relay RL2, which then supplies high negative voltages to the screen and
control grids of the power tubes to cut the tubes off. The relay, at the
same time, lights the protection lamp.
Under this condition, the antenna
output
is automatically
switched
to exciter output.
This operation
is
shown in Fig. 2.
When 400 mA or greater flows through a tube, the thyristor is turned on
by the collector current of transistor Q2. The 400 mA causes the tube to
develop 4 V across the cathode, and the voltage is applied to the emitter of
Q2 through
the diode
matrix.
This voltage at the emitter, however,
is
ry
a
on Te on
the transistor is adjusted to a base voltage of 3.0 V, the transistor develops
Advertisement
