AMATEUR RADIO

Build A
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- - a 4-1000 provides
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T
h
Nor man B. Watson W6DL
5501 Via Del VaIle
Torrance CA 90505
e ultimate station,
from the viewpoint of
most of us, woul d be o ne
located on a hill remote from
n o i s e sources, havi ng
separate, large, highly
elevated antennas for each
band. The ham shack would
contain a separate kilowatt
transmitter for each band,
pre tu ned and cor rectly
matc hed to its separate
antenna by means of an rf
bridge, and ready for instant
use. Unfortunately, not many
of us can afford such an
arrangement.
This article describes a
compromise available to all
who have the desire and perseverance
to learn and build.
Th is is a kilowatt linear
amplifier of highly efficient
and conservative design employing
band change by the
simple actuation of three
switches. In its design, space
has been conserved; however,
size has not been restricted at
the expense of efficiency,
reliabil ity, or signal quali ty.
Quite common in the
1930's and 40's was the pushpull
out put circuit using two
tubes, a bala nced tank circuit,
a n d link coupling, we ll
known for its high efficiency
and for cancellation of even
o rder harmonics. T h e
grounded grid circuit was
known but not commonly
used. In this amplifier, the
b ala nced tank circuit is
adapted to use with a single
4-1000A tetrode, used in a
grounded gri d, grounded
screen circuit with link
coupli ng. Harmo nic distortion
prod ucts are minimized.
Efficiently tuned an d correctly
matched input circuits
are used to improve signal
quality and reduce drive requirements.
The 4-1000A is
run at an efficient plate
voltage and loafs at a kilowatt
de input.
System
Fig. 1 is a block diagram
showing the functional arrangement
of units for power
sup ply, signal amplification,
and antenna matching. The
amplifier input and output
circuits are continuously
tunable across the 80, 40, an d
20 meter bands. A tuned link
for each band feeds the output
to separate an tenna
tuners for 40 and 20 meters,
which in turn feed 95 Ohm
balanced coaxial lines. The 50
Ohm unbalanced input to the
antenna tuning unit is fed
straight thro ugh on 80 meters
to a 50 Ohm unbalanced line.
Sixty seconds is allowed
for filament heat ing before
high voltage is applied. For
tu be protectio n, the high
voltage is removed from the
tube when plate current ex-
112