©1995 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 11/27/01
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cessive power sag occurs after heat-
ing and retuning the capacitors does
not correct the problem, check to be
sure the transistor is mounted prop-
erly to the heat sink surface with
heat sink compound.
TROUBLESHOOTING.
Since the unit has only one sim-
ple amplifier stage, there isn't much
which can go wrong. The circuitry is
straightforward, with shorted coax ca-
bles or incorrect or shorted pc board
component connections being the
first things to suspect should there be
no output.
Should it be necessary to replace
rf power transistor Q1, be sure to use
an exact replacement. There are
other transistors rated at similar out-
put level, but they may have lower
gain or different impedance charac-
teristics.
To replace the transistor, carefully
peel each lead away from the pc board
while melting the solder. Then, re-
move the mounting hardware and
gently push the old transistor out of
the heatsink. Clean all the old solder
off the pc board. Add new heatsink
compound, and install new transistor
with collector lead in correct location.
Carefully tighten nut on transistor
without over-torquing. Then, flatten
leads against the board, and sweat
solder them to the board. Re member
to resolder any components removed
for access to the transistor leads.
A word about relay coils. Any relay
coil connected to the same B+ line as
solid state equipment should have a
reverse diode connected across it to
absorb the inductive kickback which
occurs when the coil is de -energized.
Relay coils and similar inductors can
cause transients up to several hun-
dred volts. This is the most common
problem related to damaged semi-
conductors. You should also be sure
that your power supply does not have
an inductive surge when you turn it
on or off. If in doubt, borrow an os-
cilloscope and watch the B+ line when
you turn the switch on and off.
PARTS LIST.
Ref Desig Description (marking)
C1
15 pf chip capacitor
C2-C3
10 pf piston trimmer cap.
C4-C5
15 pf chip capacitor
C6
mica variable #703
C7-C8
10 pf piston trimmer cap.
C9
15 pf chip capacitor
C10
.001 uf chip capacitor
C11
0.1 uf chip capacitor
C12
47 uf electrolytic cap
L1-L4
form per diagram
L2
0.33 uh rf choke
Q1
Philips BLW-81 or
Mot. MRF-653
R1
270 ohms, 1/4W
R2
10 ohms, 1/4W
Z1, Z3
Ferrite bead (remove lead
before using)
Z2
6-hole ferrite balun core
wound as per text