Power Amplifier (A8A4A1) Tube Removal and Replacement

TM 11 5820-509-35

NOTE

(n) Install the top cover with the 4-40

Install all card assemblies through

pan head screws; invert the chassis and install the

bottom cover with the 4-40 x 1/4 flat head screws.

the bottom of the module chassis

with the card notches toward the

bottom of the module and the corner

NOTE

notches to the right hand side.

Observe that the grounding fingers

attached to the bottom cover

properly engage the slotted portion

(d) Verify that the gear assembly (that

of card assembly E1.

drives the switch on card assembly E5) is also in the no.

1 position (against its maximum counterclockwise stop

3-14. Power Amplifier (A8A4A1) Tube Removal and

when viewed from the front of the module). If not, rotate

Replacement

the Geneva drive shaft that extends to the rear of the

(fig. 3-65 and 3-87)

gear assembly until the stop is reached.

(e) Install card assembly E5 through

WARNING

the bottom of the module chassis and carefully slide the

High voltages are present on circuit

D-hold of the switch rotor on to the stub shaft that

components associated with the

extends to the rear of the gear assembly.

power amplifier stage.

These

(f) Carefully insert the four 4-40 x 7/8

voltages are dangerous and can be

pan head screws (with associated lock washer and flat

fatal.

Before beginning tube

washer in place) through the bearing plate and then

replacement, ground the two high-

install the 1/2-inch spacers before securing the corners

of the card assembly.

voltage terminals (J1-A1 and J1-A2)

on the main chassis to discharge the

(g) Install the unit assembly composed

filter capacitors in this equipment.

of switch cards E6, E7, and E8 as a unit, through the

bottom of the module chassis into their respective slots

(fig. 3-15).

a. Removal.

(h) Orient the shaft couplers to agree

(1) Loosen the four 8-32 x 1/2 flat head

with figure 3-63 and carefully insert these shafts into the

screws and remove the access cover (fig. 3-87) from

switch rotors of card assemblies E7 and E8. (The gear

the front of RT-671 /PRC-47. Do not damage the

shaft that drives card assembly E5 through the switch

gasket when removing the access cover.

assembly has the drive end deeply slotted, the opposite

(2) Loosen and remove the 4-40 x 1/4 pan

shaft is not slotted on the end.)

head screws that secure the bottom cover to the power

amplifier compartment; remove this cover.

CAUTION

(3) Loosen and remove the two 4-40 x 1/8

Do not disturb the position of the

pan head screws that secure overtemperature cutout

switch rotors of card assemblies E7

K103 to the power amplifier tube heat sink (fig. 3-65);

and E8 when installing the drive

remove K103.

shafts, improper switch operation

(4) Remove the plate cap from V101 and

and equipment damage can result.

push its attached lead into the power amplifier

compartment through the clearance hole in the side of

(i) Install the triangular-shaped switch

the heat sink.

shaft retaining plates under each shaft coupling and

(5) Grasp the tube at its base and disengage

secure each in place with three 2-56 x 1/4 pan head

it from its socket. Withdraw the tube and the heat sink

screws and associated lock washers (fig. 363).

together through the access hole in the front panel of

(j) Insert card assemblies E4, TB1, and

the receiver-transmitter.

E2 in that order before installing card assembly E1 in its

(6) Place a soft pencil mark on the heatsink

slot.

opposite the oversize pin on the base of the power

(k) Install the nylon cable clamp using

amplifier tube. Gently pull the heat sink from around the

the 4-40 x 3/16 flat head screw.

tube.

(l) Insert the metal partition between

b. Replacement.

card assemblies E4 and E5 and secure it in place with

(1) Insert a new power amplifier tube in the

the four 4-40 x 1/4 flat head screws (two per sides.

heat sink using care to observe the orientation of the

(m) Thread the interconnecting wire

oversize pin on the tube base.

from E4 through the hold in the metal partition and

(2) Insert the tube and its heat sink through

attach and solder it to the proper terminal on card

the front panel access hole and press the tube firmly in

assembly E5 (fig. 3-14).

to its socket.

3-103