Internal view showing mounting arrangements.
The anode connection is made from a thin brass strip and the grid ring
turned from brass (G4VVT).
The PA output Pi section consists
of 2 variable Cs (20 - 120pF and a second (home made) 50 - 450pF switched
in for the lower bands by a simply modified 12v power relay).
The PA coil is in two section.
8.5t x 2" dia (3/16th Cu tube)
- 3" long
tapped at 4t (28MHz),
6t (18, 21, 24MHz) and 8.5t (10, 14MHz)
30t x 2" dia (12swg Cu wire) -
5" long
tapped at 10t
(7MHz), 18t (3.5MHz) and 30t (1.8MHz).
The anode choke (200t, 24swg 5"
long on 1" dia PTFE tube stock) is mounted directly onto a 3300pF 10kV doorknob
capacitor using a small turned brass ferule.
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The grid compartment. The
main fan blows into the sealed grid compartment, and exits through holes
around the grid bases to flow through the PA chimneys. The heater/cathode
connections are again made from thin brass strip. The heater choke is
wound on ferrite rod (from a scrap transistor radio, bifilar 28t 10swg).
The input circuit consists of a
100ohm non-inductive 50Watt resistor (Farnell - about £3) directly across
the input. The grid load is also about 100ohm under normal operating conditions
so the input VSWR should be quite good.
Some SWR variations are expected
depending on drive levels but the SWR should remain within limits for a typical
100W HF transistor rig (eg IC735)
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