Tuning Power Amplifier-continued

TM 11-5820-509-12

b. Set OPR/TUNE switch to TUNE.

PWR switch to OFF for a minute before

repeating e below.

CAUTION

e. Immediately adjust the POWER AMPLIFIER TUNE

Do not allow the power amplifier to

control and then the POWER AMPLIFIER LOAD control

remain keyed for more than a few

to obtain maximum deflection on the XMTR OUTPUT

seconds at a time while tuning, since

meter. If the antenna being used has a length greater than

excessive dissipation tends to burn out

15 feet, check for crossover frequencies. A crossover

the vacuum tubes and serious damage

frequency is one where the antenna in use is too long to be

can result to components of the output

properly resonated at the operating frequency and is

circuit.

readily detected by an increase in XMTR OUTPUT meter

c. Refer to figure 3-2 which is the same chart that is on

deflection as the POWER AMPLIFIER LOAD control is

the receiver-transmitter front panel. On POWER

rotated to 0.

AMPLIFIER LOAD and POWER AMPLIFIER TUNE

NOTE

controls (fig. 3-3), loosen lock knobs. Adjust the turns

counters of the controls to the settings indicated on the

Proper output circuit resonance is

LOAD TUNE chart as follows. The outer scale of each

normally obtained without rotating the

turns counter is numbered in units from 0 to 39 and

POWER AMPLIFIER TUNE and

represents the whole-number part (coarse tuning) of the

POWER AMPLIFIER LOAD controls

turns count shown on the LOAD- chart (fig. 3-2). The

more than 3 turns from the initial

inner scale of each turns counter (fig. 3-3) is numbered

setting in c above.

from ~ to 100, and this scale makes 1 complete rotation

f. Again rotate the POWER AMPLIFIER LOAD and

per outer scale unit division. The inner scale represents

the POWER AMPLIFIER TUNE controls in either

the decimal part (fine tuning) of the turns count. For

direction to obtain a maximum indication on the XMTR

example, suppose it is desired to resonate the output

OUTPUT meter. Note maximum deflection value.

circuit to an operating frequency of 5.5 MHz and load a

Rotate POWER AMPLIFIER LOAD control

15-foot whip antenna. The proper initial setting for the

clockwise (increasing load) until the indication on the

outer scale TUNE control is indicated on the chart at the

XMTR OUTPUT meter drops one or two divisions.

intersection of the dashed lines marked TUNE with an

h. Readjust the POWER AMPLIFIER TUNE control in

imaginary line extending vertically from the 5.5-MHz

either direction to obtain a maximum deflection on the

frequency scale. This value is read on the left- scale

XMTR OUTPUT meter. Note the maximum value of

(KNOB TURNS) of the chart as 15 (approximately).

deflection.

Similarly, the outer scale LOAD control setting is

i. If the maximum indication obtained is greater than

indicated on the chart at the intersection of the solid curve

the value in f above, repeat g and h above until the

marked 15 FT LOAD and the imaginary line extending

absolute maximum value is obtained. If the XMTR

vertically from the 5.5-MHz frequency scale. This value

OUTPUT meter indication of h above is less than the

is also read on the left-hand scale of the solid curve that

indication of f above, rotate the POWER AMPLIFIER

agrees with the length (15, 25, or 45 foot) of the antenna

LOAD control counterclockwise (decreasing load) until

being used, and adjust the outer scale turns count to

the deflection of XMTR OUTPUT meter decreases two or

provide the proper frequency of operation.

three divisions. Readjust the POWER AMPLIFIER

TUNE control in either direction for maximum deflection

WARNING

on the XMTR OUTPUT meter. Repeat until absolute

Do not touch the antenna above the

maximum deflection is obtained.

threaded stud during transmission.

j. Set the XMTR PWR switch to HI and immediately

Serious injury or DEATH could result.

peak the XMTR OUTPUT meter deflection by fine

d. Set the XMTR PWR switch (fig. 3-1) to LO.

adjustments of the POWER AMPLIFIER LOAD and

CAUTION

POWER AMPLIFIER TUNE controls as indicated in f

Do not allow the XMTR OUTPUT

through i above.

meter needle to peg off-scale; always

k. Return XMTR PWR switch to OFF, and carefully

reduce the deflection slightly by

tighten the LOCK knob to secure the turns counters of the

adjusting the M ADJ control

POWER AMPLIFIER LOAD and POWER AMPLIFIER

counterclockwise.

If maximum

TUNE controls.

deflection is not obtained, reset XMTR

3-5