The other three-phase half-wave rectifier consists of
power-supply transformer T8K, filament transformer T7K,
249B vacuum tubes V8K, V9K and VlOK, choke coil L6K, load
resistor R3K - R4K, and voltmeter multiplier R5K with its
protector PRlK.
It supplies approximately 1200-volts d-c
for biasing the grid of the 298A tube V2D of the D-99118
power amplifier. Filter condensers for this rectifier are
located in the D-99118 unit D.
Taps are provided on T7K for adjusting the filament
voltage of V8K, V9K and VlOK to a value close to 2. 5 volts.
Taps on the primaries of T8K permit a variation of the rec
tifier output voltage.
They should be set for a value as
close as possible to 1200 volts.
Special D-99ll4 Rectifier Unit
(
Unit G,
Schematic Figure 3A
)
Circuit Description
The plate-rectifier circuit of this assembly contains
the six mercury vapor tubes VlG to V6G inclusive, connected
in a three-phase full-wave circuit. The tubes convert the
three-phase high-voltage power furnished by transformer
T58P into unidirectional current which, after being filtered
(
by L52P and FC51P
)
, supplies the plate current of the two
power amplifier tubes in Unit C, for 5-kw emergency opera
tion. The seventh tube, V7G, is kept in operating condi
tion by heating its filament at a reduced voltage obtaiRed
through resistances R3G and R4G.
In case of failure of any
of the other six tubes, this tube may be substituted; it is
ready for instant operation. During regular 50-kw opera
tion, the filaments of tubes VlG to V7G inclusive are
heated at reduced voltage to facilitate rapid "cut back" to
5-kw, should this become necessary.
An
overloai relay, SlG, is provided to indicate exces-
16
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