Western Electric 407A-4, Instruction Manual

Page: 63 / 136

V2D at jack JlD. Coil LSD and resistance R6D provide a small
part of the output of the amplifier at terminals 61 and 62 to
be us_ed for stabilized feedback.
Between the transmission-line coupling coil LlD and the
line there is connected a radio-frequency harmonic filter con­
sisting of coil L2E and condensers C2. 1E, C2. 2E, C3. 1E, C3. 2E,
C4. 1E, and C4. 2E. Additional harmonic suppression is af­
forded by an auxiliary transmission line connected across the
input terminals of the main line. The current fed into the
main transmission line is indicated on M2E.
Connected respectively to the radio-frequency input bus_
and to a tap on L7D are two coils LlOD and LllD, associated
with a protective device which also serves as an overall
tuning indicator for the amplifier. The other elements in
this protective device are the rectifier tube VlD, with its
filament transformer T4D and filament by-pass condens ers
Cl2
.•
1D and Cl2. 2D; the shunting resistance RBD for this tube,
with a disabling switch D3D ; a relay S3D; and a d-c milliam­
meter MlD for reading the rectified output of VlD.
The high-voltage plate supply is fed to the power ampli­
fier through plate choke coil L4D. The two grid-bias sup­
plies are fed to the tu bes through grid chokes L3D and LBE,
the higher bias being employed for V2D. The grid-bias volt­
age for V2D is filtered by C8D through a stabilizing resistor
R9D. C BD
is
protected against abnormal voltages b y thyri te
protector PRlD. The corresponding grid-circuit equipment
for VlE consists of CSE, R9E, and PRlE ,
The plate currents of the individual tubes are indi­
cated on M3D and MlE and the total plate current on M2D.
These meters are equipped with shunts R4D, R4E, and R5D.
The Overload relays SlD and SlE are likewise equipped with
shunts, designated R3D and R3E.
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