[AMPS] Re: 8k ultra/ "tuned input"

[Phil Clements]

A few words in defense of Henry is in order here....

> >-henry  doesn't  change  the  bias  on  cw/ssb.   The  bias   consists  of
> >15-20  diodes  in  series  in  one  block  like  a  W2AW  module.   The
> >idle  current  zsac   goes  up  and  down  cuz  of  plate  V   difference
> >between  SSB  V  and  lower  cw  V.    Manual  sez  no  load  HV  on  ssb
> >should  be  5400V  .  Henry  uses  a  6kv   plate  xfmr  with  a  choke
> >input.....     .9  x  6000=  5400V.    They  also  suck  a  continuous
> >300W  of  bleeder  power  all  the  time  to  make  the     tuned  choke,
> >look  like  a  choke.

The 3CX3000A7 runs just fine with zero bias. Henry elected to add a little
bias to cut down a bit on heating of the operating area, which Texans
appreciate. With a 3X3 throttled back to 3500 watts PEP, several things
can be done that might not look kosher to someone designing for 6000
watts.
> > If  any  of  the   5  x  100 watt  bleeders  ever
> >opened  up,  the  HV   would  skyrocket  to  8485V. And  that's  if  you
> >have  the  correct  tap  to  start  with.
> >
> //  However, the filter capacitor could probably take the surge.  When
> the amplifier was keyed, the ZSAC acts as a bleeder current.

Amen, Rich...if a bleeder failed during key-down, you still have at least an
800 watt load on the HVPS from the ZSAC from the 3X3. The filter caps
are 2X-16 mfd @ 7.5 kv oils.  An 8400 volt surge during bleeder failure
is no big deal here.

>
> >    The  fil  V  should  be  below   7.5  V  measured  right  at  the
> >socket.    Life  of  tube  is  dependent  on   fil  V.    If  the  tube  is
> >lit,  the  clock  is   ticking.   The  tube  won't  last  any  longer   cuz
> >you  are  running  it  at   1500w  out.    If  you  had  a  2nd  amp.  with
> >just  the  tube  fil  lit,  and  no  drive  applied,  and  no  HV,  it
> >would  last  just  as  long  as  your  driven  amp.

Henry takes care of two problems in the filament circuit with one
simple part. A power resistor (R617) in the primary of the filament
transformer limits inrush current and allows setting of the filament
voltage to the correct value for whatever line voltage that may be
encountered. A filament voltmeter is included, which can be calibrated
to a precision measuring source, so filament monitoring is available
at the flick of a switch.

> >The stock  blower  on  the  8K  ultra    will  not  provide  enough  air
> >for  anywhere  near 4kw  of  anode  diss,  more  like  2500w   tops.   The
> >stock    straight  up  and  down  chimney  puts   quite  a  restriction  on
> >the  airflow.

You get what you pay for. The 8-K is rated for 3500 watts PEP MAX.
No where near 4 kw dissipation......
I restate...look at the manufacturer's design targets and specs before
making judgements of component selection. The cooling system is,
IMO, very inovative, a la the Heath SB-220. A fiberglass cylinder is fitted
from the tube anode cooler  and runs up to the top cover where the hot
air is exhausted through holes in the cover. Air enters from below deck
through holes around the tube. There is enough air available to circulate
throughout the tank circuit components before entering the anode cooler.
The ambient heat build-up inside the RF deck is many degrees cooler
than with conventional methods. Heat generated by the tube is segregated
from the other components on the deck.

> //  A high-pressure blower from Kooltronics or Rotron would cure this
> problem.  Henry engineering is apparently clueless about manometers and
> the effect of filament potential.

Not in the case of the 8-K. Those wishing to exceed Henry's specs and
operating instructions will need  to look at Rotron et al to beef up for QRO.

> >
> >The  henry  back  to  back  un-uns  are  interesting  though  I  don't
> >understand  the  theory  behind  them.     They  operate  from  1.8-30mhz
> >continuous.
>
> //     But the SWR is somewhat less than satisfactory.

The target for the 8-K was an input circuit that will guarantee <2.0-1
SWR on any frequency from 1.8-30 mhz. with a MAX drive power
of only 150 watts. Also the target for feculance was >-60 db second
harmonic and >-35 db IMD @ 3500 watts PEP output. By throttling
the 3X3 back 2500 watts and adding a gang-tuned Pi-L tank circuit,
these targets were easily met with the components Henry selected
for the job.

My guess is that if the intent was to produce a 6 kw amp with the
same specs, you would see pi network input circuits, (it would take
18-20 of these to cover 1.8-30 mhz with no gaps) a bigger blower,
and a 2.5 amp Ip meter. Also included would be a much larger price
tag!

Sometimes the end justifies the means. Amateurs today are not
used to seeing over-engineering when they look "under the hood"
of an amp. I have to admit, when Henry attempted to be competitive
in the amateur market by "dumbing down" their fabulous commercial
designs, some really bad  mistakes were made. The 8-K is not one
of these "mistakes!"

(((73)))
Phil, K5PC





--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com