[AMPS] Tune Up of Henry Amplier, Part 3 of 3 parts

[Jim Reid]

Part 2 ended with Peter's response to my misquoting of
his intent of tune up.  So continuing on to the end:

Perhaps a quick description of the 8K plate circuit would
aid here.  From the triode plate,  immediately is a series
parasitic suppressor choke.  To the input of this choke,  are
two lines,  one goes to the HV supply line via two series
RF chokes with a set of relay option selectable shunt caps
to ground (relay selects caps depending upon
band switch setting)  and a bunch of shunt capacitors
to ground on the HV line leading to these series chokes.
The other line to the input of the parasitic suppressing choke
on the plate is a set of paralleled capacitors which act as
DC isolators to the output circuit.

The input to the "pie" circuit consists of relay selected,  depending
upon the band of operation, sets of fixed capacitors.  These are
shunt to ground at the input of the first "load" controlled rotary
inductors.  At the output side of this inductor are the other set
of relay selected fixed capacitors which are controlled simultaneously
with the relays controlling the input C selections.  So the five
position band switch selects the both  network input and output shunt
fixed capacitors.  The 40 meter band switch selection capacitors
are used for all frequencies between 5 and 10 MHz; the 20
meter position,  for all between 10 and 17 MHz.  And 10 and
15 use the same fixed caps.

The servo motor driven "tune" controls a  465 pF Jennings
vacuum variable C in shunt with the fixed output
caps at the output.

The L-network output rotary inductor,  is adjusted simultaneously,
with the large "pie" network inductor by the same "load" servo motor,
via a "timing chain"  loop.  Therefor,  the "load" control adjusts
both network inductors simultaneously.

Just now,  tuned up for 40 meter CW,  I see something just below
0.5 amp of plate current, 480 or 490 mA, with the plate voltage
dropping,  key down,  closer to 5200 volts,  and the grid current
is more like 80 mA;   not 160 or 1/3 of the Ip.  The tube is a
3CX3000A7,  Eimac triode.  Drive power is 62 watts;  output,
1500 watts per the sluggish reading Bird,  hi; or just under
14 dB of gain from the 8K on 40 meters.    Looks as if the
result is about 59% efficiency of tube DC input to RF output
power. (Of course,  there is also power consumed for the
tube filament, etc.  and the rather large blower -- glad all is in
another room from my small operating room.  The blower is
quite audible and a lot of heat is blown out of the pedestal
while operating!  With the Henry Ultra,  all of this is remote
form the operating position,  with only the silent Controller
Unit on the table by the transceiver. All just great for my
small operating room for radio here in the tropics.)

Anyway,  thanks again for the refresher on the proper way to
tune up.  And BTW,  the Q of the Henry output circuit must be
fairly low,  as the "load" control,  at least monitoring output power,
is "soft",  or to put it another way,  adjusting the circuit "load"
inductors
makes little difference in output power over quite an adjustment
range.  Now maybe I will see a difference when I go back
and watch for the plate dip rather than just concentrating on
the Bird meter reading.  BTW,  the Bird seems to react very
slowly,  wish it were faster reacting,  as often fight the
apparent "hysterisis" of tweaking for the max output for
a given input drive level (this by the way is usually around
60 to 65 watts or so)

Anyway,  that's the view from here on tuning the Henry 8.

73,  Jim,  KH7M
On the Garden Island of Kauai







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