rad i o l'requ en<:y c h oke coil L5B, and anti-sing c i rcuit composed of inductance
Ll 4 1 1
a nd resi stance H l 4 B . The plate voltage is reduced by the series plate
feed res i stance R�l B . By-pass condensers C l2B and C27 A connected in parallel
th rough term i n a ls
Hi
and 36 on the Amplifier Unit and terminals 11 and
4,
respecti vely, on the Oscil lator Unit, are p ro\' i ded across plate feed resistance
H �l l : .
The plate current is i nd i cated by meter
l\ 1 7 B
marked "THIRD AMPLI
F I E H P LATE CURRENT."
The seriL'S c i rc u i t condensers C
-
L l B , C4.2B, and C9B, connected in parallel
w i t h i n ductance LnB, constitute the output c i rcuit of vacuum tube V3B . Con
denser C�U fu nctions as a plate blocking condenser. A hand wheel, marked
"T l l I R D Al\I PLI F I E R TUN I NG," controls a sl iding contact on coil L6B and
provi des a th l'ee-turn conti nuou
s
adj ustment of i n ductance. A tap on L6B i s
etlso pro
\
·
id
e
d fol' a pprnximate ad,i ustments. Resonance is indicated b y a m i n i
m u m rea d i ng- o f the plate current meter
l\ I 7 B .
Th resi sta nces Rl7. 1 B and
R 1 7 . 2 B
a re s h u nted across condenser C9B and
serve as a load for the t h i rd a m pl ifier. The rad i o frequency current flowi ng·
th l'OUj.dJ these resista nces i s indicated by m eter l\I6B marked "THIRD AMPLI
F
I EH
LOA D
CURRENT."
The th i rd a m pl i fier is neutral ized by condenser C l 9A located in the Oscil lator
Unit and adj u sted from the front of the oscillator panel by the control marked
"TH I I � D
A j J
PLI F I E R BALANC I NG CONDENSER." D u ri ng the neutraliz ing
opera t i o n , w h ich \\· ill be described later, l ink switch D6B is opened and change
over switch
D 7 B
i s placed i n the position w hich connects low current thermo
couple H 6 . 2 B in the cl osed c i rcuit of V3B. T h e neutralized condition is indicated
L >�·
meter l\ I OB .
Pow
e
r A mplifier
R;tdio frequency grid \'Oltage for the No. 228-A Vacuum Tube is obtained
from the output c i rcuit of V3B through grid blocking condenser C5B and anti
sing- resi stance R26B. The grid bias of 250 volts is obtained from the 250-volt
generator throuirh the filter c i rcuit consisting of retardation coil L l 5B and
condensers C l 6B and C l9B , and the radio frequency choke coils LlO. l B and
L1 0 . 2 B .
The DC plate supply for V 4B is obtained from the 4,000-volt supply ter
m i rn1l through retardation coil L3B , plate current meter M2B, and radio fre
quency c h oke coil Ll l B . The plate current i s indicated by meter M2B marked
" PO\VER AMPLI F I ER PLATE CURRENT ."
The filament of V 4B is supplied from the 25-volt DC generator through
re\'ersing switch D l B . This switch is provided in the filament circuit so that
the filament current can be reversed periodically in order to prolong the life
of the filament.
The output circuit consisting of tuning condenser C7B in parallel with the
series circuit composed of tuning inductance L7B and coupling condenser C lOB,
receives its p ower from V 4B through condenser C6B. The proper tuning and
[ 34 J