4.
A check for loose nuts, screws, cables and parts.
5.
An inspection of the high- and low- voltage con-
nections.
POWER AMPLIFIER TUBE
REPLACEMENT
To remove the Power Amplifier tube, proceed as follows:
1.
Remove the high-voltage lead from P0-2, located
on the rear of the Power Amplifier.
2.
Loosen the winged screws holding the rear cover
plate to the assembly.
3.
Slide off the rear cover plate.
4.
Insert the prongs of the tube extractor (included
with the station equipment) between the cooling
fins of the PA tube plate.
5.
Pull the tube straight out from the socket.
To reinsert the Power Amplifier tube, proceed as follows:
1.
Insert the prongs of the tube extractor between the
cooling fins of the PA tube plate.
2.
Push the PA tube all the way into the socket while
observing the key on the tube and socket. The tube
extractor may be left on the tube cooling fins.
3.
Replace the rear cover plate of the Power Amplifier.
4.
Tighten the winged screws on the rear cover plate.
5.
Replace the high-voltage lead to P0-2 on the rear of
the Power Amplifier.
BLOWER
The blower motor bearings are to be lubricated every
2000 hours of operation. A small oil can for this purpose is
mounted on the power supply chassis, at the right of the
blower motor. Use the oil recommended in the Parts List.
(See Parts List on back of Schematic Diagram.)
MULTI-FREQUENCY OPERATION
1.
Tune the PA on the LF (lowest frequency).
2.
Select the HF (highest frequency) and re-peak the grid
tuning.
3.
Select LF and adjust the PA plate tuning CW (clock-
wise) to let the plate current rise 5 - 10 mA.
4.
Then re-adjust the screen control for rated plate cur-
rent level.
5.
Select HF to compare the plate currents.
6.
If there is greater than 10 mA difference then repeat
the step at the lowest frequency (LF) by adjusting the
plate tuning control CW for another 5 - 10 mA in-
crease.
7.
Re-set the screen control for rated plate current and
compare the highest frequency current again.
8.
Continue this process until there is less than 10 mA
difference at the two frequencies.
ALIGNMENT PROCEDURE
This Alignment Procedure is provided for completely re-
aligning and loading Power Amplifier Models 4EF4A1, 2, 3
(using KT-56-A as a Driver Unit) in a KT-39-A transmitter.
Before tuning the Power Amplifier, the Driver (KT-56-A,
C) must be aligned according to the Driver ALIGNMENT
PROCEDURE.
1.
Connect the antenna or some other suitable 50-ohm
load to the top jack on the Power Amplifier antenna
relay.
2.
Turn the PLATE switch OFF on the PA Power Supply.
3.
Tune the SCREEN adjust on the PA Power Supply
fully counterclockwise.
4.
Place the power switches located on the Power Panel
and Driver Power Supply to the ON position. Turn
the PA Power Supply Control switch to the ON posi-
tion. Allow 15-minutes for warmup.
5.
Connect a microphone to the MIKE jack (J1215) on
the back of the station control shelf mother board.
6.
Loosen the locking ring on the PA COUPLING con-
trol and push the control in and turn fully counter-
clockwise. Rotate the meter switch on the POWER
PANEL to TX Driver and meter switch on Re-
ceiver/Exciter door to position 10.
7.
Key the driver and adjust the Power Control potenti-
ometer on the driver PA for approximately 2 amperes
of driver PA collector current (0.6 V on 3 V scale of
tune-up meter) Rotate meter switch on power panel to
PA GRID. Tune the PA GRID for maximum voltage
on the tuning meter and then readjust the power con-
trol potentiometer for the following voltage on that
meter:
4EF4A1-2
0.75 VDC
4EF4A3
2.0 VDC Min. (2.5 VDC Msx:)
8.
Turn the PLATE switch on the PA Power Supply to
the ON position.
9.
While keying the Driver, adjust the PA Plate control
for a minimum reading at the PA PLATE current me-
ter. Do not exceed 275 mA of plate current. Retune
the GRID per STEP 7.
10.
Rotate the meter switch on the Power Panel to For-
ward/Reverse position. Rotate the Reflectometer to
the Forward position.
11.
While keying the Driver, adjust the PA FILTER con-
trol for maximum meter reading.
12.
While keying the Driver adjust the SCREEN control
for 250 mA on the plate current meter.
Figure 1 - Power and PA Plate Current Levels
Make sure the PLATE switch on the PA POWER
SUPPLY is in the OFF position.
NOTE
The current readings on the meter includes ap-
proximately 25 mA of screen current.
NOTE
ALIGNMENT PROCEDURE
25-50 MHz, 300-WATT
MASTR II POWER AMPLIFIER
MODELS 4EF4A1, 2 & 3
LBI-4938
LBI-4938
2
Summary of Contents for MASTR II 4EF4A1
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