[AMPS] Re: CW/SSB Tune Up

Jim Reid jimr.reid@verizon.net
Tue, 9 Oct 2001 13:15:51 -1000

Hi again,

And thanks a bunch to the several who have commented
and made specific tune up recommendations!  Have
followed them this morning.  Rich,  I chickened out at
just about 345 watts of drive,  hi.  The grid current was
approaching/bit exceeding 300 mA; Henry manual says
to not exceed 350 mA.  All of this into the Bird
load,  of course.  Bird 43 with a 5kW slug was of no use,
it is way too slow and does not respond to the 50 wpm

Anyway I found that once the tune and load controls were
at resonance,  they did not seem to need to be tweaked
as the drive was increased beyond 100 watts or so.  Hope
this is correct,  or perhaps I need better instrumentation
to "see" the correct peak output power. But see the next

I dug out the data sheets which came from Henry when the
unit was delivered.  Per the factory data,  there is a difference
in the tune/load settings between 2500 and 5000 watts out.
I presume this to be constant Pout,  not just peak.  For example,
on 20 meters (14200 test freq.),  the dial calibrations for 100
watts drive,  yielding about 2500 watts out,  tune is at a dial
reading of 155,  and the load capacitor at 700 (a 1000 reading
would indicated full load C "mesh" or max C).  With 200 watts
drive,  factory data shows tune dial at 160, and the load C is lower,
at a dial of 460 or seemingly significantly heavier loading of
the output.  Maybe I should do this all over again and just
use constant key down for the final tweaking.

Another interesting point from the Henry manual.  The amp has
two plate voltage selections.  With today's mains voltage here
on the island,  in the SSB "mode",  amp not keyed,  the plate
voltage sits at about 5800 V.  In the CW "mode",  the voltage
is dropped to about 4300 V.  The Henry manual asks that one
tune up in the CW mode for max output.  THEN switching to the
SSB mode higher voltage "As long as your load has not changed,
the amplifier should still be in tune.  You can fine tune by alternately
adjusting TUNE and LOAD while driving the amp with a
constant input."

Well,  maybe all of this fiddling is of no point,  as I lower
the drive well down before going to the antenna set up!

73,  Jim  KH7M

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