©1999 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 12/11/02
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GENERAL INFORMATION.
The Power Amplifier is a class C
device designed to be installed as an
integral part of a transmitter enclo-
sure in a repeater installation with a
2 Watt exciter module.
This PA comes in models for sev-
eral vhf bands and power levels as
follows:
LPA 2-15R 140-175 MHz 17-20W
LPA 3-15R 213-233 MHz 17-23W
LPA 6-25R 50-54 MHz
20-25W
The Power Amplifier operates on
+13.6 Vdc at about 4 to 5 Amp, de-
pending on output power level. It has
a 50-ohm input and output imped-
ance and is designed for continuous
duty.
A low-pass filter reduces harmonic
output to very low levels. The unit is
FCC type accepted for commercial
operation in the 150-175 MHz band.
CONSTRUCTION.
General.
Most of the pertinent construction
details are given in the component lo-
cation and schematic diagrams and
parts list.
All parts are tack soldered to the
pc board; so it is necessary to cut and
form leads so that they seat properly
on the board and be sure to keep
leads as short and direct as possible.
This is especially true of the disc ca-
pacitors. Figure 1 shows how to trim
and form the leads of capacitors.
PCB, Transistor, and Heatsinking.
This series of power amplifiers is
designed to be mounted in an rf tight
enclosure with the exciter in such
applications as our REP-200 Re-
peater. The unit is supplied less
heatsink and mounting hardware,
since the enclosure acts as a heatsink
and the hardware normally is pro-
vided with the repeater kit.
If you have purchased the PA for
some other use or mounting method,
it is important to assemble and use
the unit as we do in the repeater to
avoid damage to the transistor by
pulling the leads off the ceramic case.
The pa is designed to have the thick-
ness of a standard 4-40 nut (about
0.100 inch) as a spacer between the
pc board and the chassis on which
the transistor is mounted.
a. If you are supplying your own
enclosure, mark and drill four clear-
ance holes for mounting the board
with 4-40 screws and one 8-32 clear-
ance hole to mount the transistor in
the center of the cutout in the board.
The latter hole must be close to the
diameter of the xstr stud to provide
maximum surface for the shoulder of
the transistor to contact the chassis
for heatsinking; so do not make this
hole oversize.
b. Install four 4-40 x 3/8 inch
screws from the bottom of the enclo-
sure and secure with 4-40 nuts.
c. Set pc board over screws, and
align so cutout for transistor is cen-
tered over hole in enclosure. Secure
the board with 4-40 nuts and lock-
washers.
d. Carefully open the package of
heatsink compound with scissors.
Use a toothpick or small piece of wire
to apply a small amount of compound
to the shoulder of the transistor
where it contacts the heatsink.
e. Set the transistor in place, and
orient the notched collector lead to
the right as shown. Secure transistor
with #8 lockwasher and 8-32 nut. Do
not overtighten nut; tighten only to
the point of being snug. Hold transis-
tor leads with fingers to prevent rota-
tion. If leads still rotate, you are
probably applying too much torque.
Note: Since heatsink compound is
used, it is unnecessary to use a lot of
torque, which could break the stud.
f. Form the transistor leads down
against the board. Then, tack solder
them to the foil, using sufficient sol-
der so that a bond is formed under
the full length of the leads. Note that
other parts will be soldered on top of
the base and collector leads; so it
helps to thoroughly flood those leads
with solder.
Installing Capacitors.
a. Solder variable mica capacitors
C8 and C9 to the board in the exact
positions shown in figure 2. Mount
the capacitors oriented as shown so
the rotor screw is connected to the
proper side of the circuit (as shown in
fig. 2).
b. Bend the leads of C2 and C3
gently at a 90° angle, and solder them
as shown. Make sure the round end
of C2 goes to ground.
c. Form the leads of C1 and C15
(if used) close to the body, as shown
in figure 1, and tack solder on the
board.
d. Tack solder C4-C5 and C6-C7
(if used) as shown, bending the leads
at right angles, and keeping them as
short as possible, as shown in figure
1. It is important to angle the capaci-
tors as shown in figure 2 and position
them as close as possible to the body
of the transistor. The idea is to con-
nect them electrically as close as pos-
sible to the emitter and base
terminals or the emitter and collector
terminals. In fact, they should be
soldered on top of those leads.
e. Tack solder C13 and C14 as
shown, bending the leads at right an-
gles, and keeping them as short as
possible. Position the capacitors as
shown in figure 2.
f. Tack solder chip capacitors C10
and C11 as follows. Position the ca-
pacitors as shown in figure 2 or 5.
They are installed between the B+
pad and ground. Use small tweezers
to handle them.
Be careful not to
drop them; they are difficult to find.
Since they have no markings, be sure
to leave them in the package until in-
stallled so you can tell the values
apart.
Apply a little solder to the B+ pads
adjacent to where each capacitor will
be positioned. Do not apply solder to
the ground plane yet.
Pick up one capacitor at a time.
Set the capacitor in place. Then, heat
the solder on the pc board pad, and
allow the solder to bond to the elec-
trode on the capacitor. When the
solder melts, the capacitor will seat
down on the board in the molten sol-
der. It is essential that this process
be done relatively quickly so the sol-
der doesn't oxidize and so there is
still a little flux left where the capaci-
tor electrode sits.
After one end of each capacitor is
soldered and the positions have been
checked, solder the ground plane end
of each capacitor.
g. Tack solder electrolytic capaci-
tor C12. Bend the leads at right an-
gles, and observe polarity.
HAMTRONICS® LPA 2-15R, LPA 3-15R, & LPA 6-25R
REPEATER POWER AMPLIFIERS:
ASSEMBLY, INSTALLATION, & MAINTENANCE
