Western Electric 407A-4, Instruction Manual

Page: 50 / 136

ground. Each tube s pace current is measured by the drop
across meter shunts that are provide d in the c ir cu its . The
output circuit of V4A and V5A is conne cted to terminal 65,
so that audio-frequency power is connected to the D-151135
modulating amplifier acros s terminals 65 and 61 in series
with the radi o-frequency output ac ros s terminals 54 and 55.
The audio plate blocking condenser is provided in the
D-1 51135 modulating amplifier.
The radio-frequency rectifier tube VlOA, as s ociated with
its input transformer T9A and output trans former TllA, fur­
nishes a means of audi-frequency monitoring .
Power -Supply Circuits
The fi laments of all vacuum tub es in the os cill ator­
amplifi er unit are heated by alternating curr ent from trans ­
formers T2A and T 3A. A s ingle-phas e full -wave rectifier em­
ploying me rcury-vapor tubes Vl2A, Vl3A, Vl4A, and Vl5A
(
with
Vl6A as a spare
)
supplies all screen and plate potentials .
The 19wer potentials are obtained from s liders on the poten­
tiometers as sociated with the filt er circu its of the recti-
fier.
Circuit
With the "Power " and "Plate Recti fier" controls in the
110FF11 pos iti on, place vacuum tub es in their res pective
sockets ac cording to Tab le 9 .
Turn the 11Power n switch 110N11 and al low sufficient time
for al l vacuum-tub e filaments to become pro perly heated.
For normal operation the heating t ime is automatic ally
taken car e of by delay circuits . However, the filament s of
new mercury-vapor tubes should be heated at leas t 15 min­
utes b efore the high voltage is app lie d. This preheating
removes any particles of me rcury adhering to the sides or
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