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Page Title: Rf Tuner, 400-700 Mc, Dynamic Circuit Analysis
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cavity and serves as an rf bypass.
acorn-type electron tube cannot be
The B+ voltage is applied through
u t i l i z e d , and a smaller envelope-
rf choke L518 to the plate (pins
type 6T4 tube is employed. Oper-
1 and 7) of the oscillator tube
ating potentials are applied to the
and to one of the l/2-wavelength
t e r m i n a l s at the base of the tube
parallel transmission lines in
socket as follows:
t h e oscillator plate circuit. The
(a) Heater voltage is connected from
second parallel transmission line
t h e power supply through feed-
o p e r a t e s at dc ground potential.
t h r o u g h capacitor C528 (A, fig.
7 3 ) which penetrates the oscil-
l a t o r compartment. Bypass ca-
54. Rf Tuner, 400-700 Mc, Dynamic
pacitor C529 decouples rf energy
Circuit Analysis
i n the heater circuit from the
heater power supply line. A short
T h e dynamic circuit analysis for the
length of wire connects the heater
400-700-mc rf tuner is identical with that
v o l t a g e through rf choke L516
for the 700-1,000-mc tuner (para 52)
to one side of V504 heater (pin 4).
except for substitution of applicable refer-
The heater voltage return path is
e n c e symbols and the following circuit
through rf choke L515 to chassis
a. V503 Input Circuit. No pickup loop is
(b) G r i d bias for oscillator V504 is
employed for coupling the rf energy from
d e v e l o p e d by the voltage drop
the first to the second coaxial-type tuned
a c r o s s grid resistor R509. The
cavity. Because a pickup loop at the lower
c a t h o d e (pin 5) is connected
f r e q u e n c y range of 400- to 700-mc must
through rf choke L517 to chassis
be considerably longer than that employed
in the upper frequency band (700-to 1,000-
(c) The 105-volt dc potential is ap-
mc), undesirable resonances in the tuning
plied to the plate (pins 1 and 7)
range can be created. Instead of a pickup
of the oscillator tube only w h e n
loop, an aperture of proper dimensions for
the front panel band selector
the pass band of the frequencies desired is
(S503) is rotated to the 400-700 -
c u t into the wall separating the first and
mc position. The dc potential is
second input tuned cavities. This aperture
a p p l i e d through two rf chokes,
method of coupling permits ample transfer
t w o feedthrough capacitors, and
of rf energy from the first to the second
one resistor. The first choke,
input cavity. Except for the difference in
L519, is outside of the rf tuner
coupling methods, V503 amplifier employs
and in series with terminal 2 on
b a n d selector S503 (front sec-
reference symbol C520 as the ganged
tion) which applies B+ potential
t u n i n g capacitor. Metallic tab capacitors
t o V504. Feedthrough capacitor
C580 and C590 permit vernier tracking of
C527 penetrates the  c h a s s  is;
the amplifier and oscillator sections of the
h o w e v e r , this capacitor serves
t u n i n g capacitor.
only as a convenient tie point for
b. V503 Output Circuit. Section C of
t u n i n g capacitor C520 loads the single-
a n c h o r i n g one terminal of cur-
tuned coaxial line in the amplifier output
rent-limiting resistor R511 to
circuit. Metallic tab capacitor C600 serves
t h e exterior of the chassis (A,
f i g . 73). The B+ voltage is de-
the same function as metallic tab capac-
itor C570 for the 700-1,000-mc rf ampli-
creased by fixed resistor R511 to
the proper value for tube opera-
t i o n . The low-potential side of
c. V504 Oscillator Circuit. Section D of
tuning  c a p a c i t o r C250, mechanically
R511 is connected to feedthrough
ganged with amplifier sections A, B, and
c a p a c i t o r C526 which penetrates
C of C520, provides the tracking frequency
the exterior wail of the oscillator

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